Runway incursion

Investigation summary 

What happened

On 15 July 2024, a QantasLink De Havilland Aircraft of Canada Limited DHC-8-402, (Dash 8), registered VH-QOD, was taxied to reposition to a different bay at Wagga Wagga Airport, New South Wales. This repositioning required the Dash 8 crew to taxi out onto the runway and then return to a different bay. As the Dash 8 entered runway 05, the crew were unaware that a Piper PA-28, registered VH-XDK, operating on a training flight by the Australian Airline Pilot Academy (AAPA), had already commenced its take-off roll from the opposite end of the runway. 

The instructor of the PA-28 was aware of the Dash 8 taxiing and assumed that the Dash 8 had received and understood their previous positional broadcasts. However, the crew of the Dash 8 were not aware of the PA-28 preparing for take-off on runway 23.

Upon entering runway 05, the Dash 8 was notified by a preceding aircraft that had landed, that there was another aircraft taking off from runway 23. The captain of the Dash 8 immediately stopped the aircraft and engaged reverse thrust to clear the runway. Simultaneously, the PA-28 pilot rejected their take-off from runway 05. 

What the ATSB found

The ATSB identified that during ground-based repositioning, the Dash 8 was unaware of the PA-28 that was taxiing for take-off on an opposing runway. This led to a situation where the crew of the Dash 8 had an incomplete comprehension of the ground-based traffic.  

Without any prior alert or expectation of the presence of the PA-28, the Dash 8 crew did not visually detect the PA-28 on take-off from the reciprocal end of the runway, prior to the Dash 8 entering the runway to taxi to the terminal. The PA-28 presented a difficult visual target due to its size and orientation over the 1,700 m distance, making unalerted detection unlikely.

Once made aware of the potential conflict of collision, the captain of the Dash 8 immediately reversed the aircraft away from the preferred runway without confirming that no other aircraft or obstacle was behind the Dash 8.

While the pilot of the PA-28 gave all the required radio calls, they did not directly communicate with the Dash 8 crew to identify the possible conflict, then positively arrange separation. Additionally, the Dash 8 ground-based reception, on VHF communications panel radio 2, had reduced strength and clarity. 

The QantasLink radio procedure required crew to use the number 2 VHF communications panel radio to broadcast and receive on local frequencies during operations at a non-controlled aerodrome. This likely reduced ground-based reception strength and the likelihood of the Dash 8 hearing other traffic in certain circumstances.

Reduced VHF ground-based communication was identified at the eastern end of runway 23 at Wagga Wagga Airport. Local operator reports and procedures indicate that reduced communication strength and clarity can be experienced on the eastern end of taxiway A to other areas of the airport.

During taxi for take-off, the PA-28 was not broadcasting transponder information, which also did not identify them to other traffic in the vicinity of the aerodrome. The AAPA procedure requiring the selection of the transponder to ‘ALT’ before entering the runway, rather than prior to taxi, became a missed opportunity to provide electronic enhancement of situational awareness to other airport operators. 

What has been done as a result

ATSB issued a safety advisory notice (AO‑2024‑041‑SAN‑01) to advise pilots and operators to review their procedures to ensure that mode S transponders are on from first movement of the aircraft. 

AAPA has advised the ATSB that changes have been made to its PA-28 Flight Crew Operating Manual, and Quick Reference Handbook, which reflects the transponder being selected to ALT mode after start in both the checklist as well as being incorporated as part of the scan action flow.

On 6 December 2024, De Havilland Aircraft of Canada Limited issued 2 flight operations service letters relating to radio communications, with one covering Dash 8 100-300 series aircraft and the other covering the Dash 8 400 series aircraft. The service letters remind operators that ground‑based VHF communications are affected by line of sight and can be impacted by buildings, terrain or aircraft structures and that use of VHF COM 1 is more effective for ground-based communications with other aircraft on the ground. 

The airport operator had issued a notice to airmen (NOTAM) notifying aircraft of a potential radio black spot at Wagga Wagga Airport under some conditions. 

QantasLink issued a safety alert notice encouraging crew to consider additional precautions when taxiing for departure or any other manoeuvring on-ground at Wagga Wagga Airport. This advice was issued due to on-ground VHF communications between aircraft possibly being affected by obstacles in the line of sight.

Safety message

Communication and self-separation in non-controlled airspace is one of the ATSB’s SafetyWatch priorities. Wherever you fly, into either non-controlled or controlled aerodromes, maintaining a vigilant lookout at all times is important. Situational awareness and alerted see-and-avoid is an effective defence against collision and good airmanship dictates that all pilots should be looking out and not be solely reliant on the radio for traffic separation. Being aware of other nearby aircraft and their operational intentions is important.

Effective use of all available sources of information is an effective risk control to achieve enhanced situational awareness and an accurate mental model of other traffic at a non‑controlled aerodrome.

Pilots are reminded that although accurate and timely radio calls play a critical role in ensuring collision avoidance in uncontrolled airspace, they cannot assume from an absence of other radio calls that there is no conflicting traffic. This is particularly important in an environment where there is high expectation of mixing with other aircraft of different sizes, flight rules and performance levels operating at the same time, in the same airspace. 

Pilots can enhance their situational awareness and mutual traffic separation by: 

• making the recommended broadcasts when in the vicinity of a non-controlled aerodrome
• actively monitoring the common traffic advisory frequency while maintaining a visual lookout and constructively organising separation through direct contact with other aircraft
• ensuring mode S transponders, where fitted, are selected to transmit altitude information before taxiing
• not hesitating to contact another aircraft if there is any uncertainty as to their position and/or intentions. 

The ATSB SafetyWatch highlights the broad safety concerns that come out of our investigation findings and from the occurrence data reported to us by industry. This investigation report highlights the safety concerns around reducing the collision risk around non-towered airports.

The occurrence

On 15 July 2024, a Piper Aircraft Corporation PA-28, registered VH-XDK, operated by the Australian Airline Pilot Academy (AAPA), with an instructor and student on board, taxied from the apron at Wagga Wagga Airport, New South Wales (Figure 1) for a training flight. At 1609 local time, the crew broadcast they were taxiing for runway 23 (Figure 2, position A). About 20 seconds later, the crew of an inbound Saab 340 responded, asking for the call sign to be repeated. The Saab 340 was 30 NM away at this stage and could not understand the call sign, even when repeated twice more. About 5 minutes later at 1614:12, the crew of the Saab 340 broadcasted that they were now on a 10 NM straight in approach for runway 23 (see Appendix A – CTAF Recordings).

At about the same time, the 2 crew members of a QantasLink De Havilland Aircraft of Canada Limited DHC-8-402 (Dash 8), registered VH-QOD, were on board the aircraft at the Wagga Wagga Airport apron. The crew were making preparations to reposition the aircraft from the apron to another bay (on the apron) by taxiing the aircraft via the runway (Figure 1). The Dash 8 crew reported they spent about 5 minutes[1] preparing the aircraft on the flightdeck prior to taxiing. However, they did not recall hearing the initial taxi call and callsign repeats from the PA-28, but did recall hearing the 10 NM inbound call from the Saab 340. 

Figure 1: Intended taxi routes for aircraft

Source: Google Earth, annotated by the ATSB

At 1616:27 the Saab 340 crew broadcast that they had joined a 5 NM final for runway 23. 

At 1617:31 (Figure 2, position B, Dash 8) the Dash 8 crew broadcast that they were taxiing for runway 05. At this time, the PA-28 was on taxiway A, approaching runway 23 (Figure 2, position B, PA-28). 

Figure 2: Position of respective aircraft at given times

Source: Google Earth, annotated by the ATSB. Note: aircraft not to scale

Being aware only of the inbound Saab 340, the Dash 8 crew communicated directly with them. This was to gain an understanding of the Saab 340 crew’s intentions on landing and exiting the runway. While still taxiing towards the runway at 1618:32, the Dash 8 crew told the Saab 340 crew of their intent to enter and backtrack from the threshold of runway 05, keeping out of the way of the Saab 340’s landing.

The instructor of the PA-28 recalled hearing the radio calls from both aircraft during this time. The PA-28 was aware of the Dash 8 taxiing for runway 05 and assumed that the Dash 8 had also heard their earlier calls, and would hold short of the runway for their departure. 

At 1619:20, the PA-28 was positioned on runway 23, with strobe lights on, behind the landed Saab 340 and the instructor made a ‘lining up and holding’ call (Figure 2, position B, PA-28). About 30 seconds later the Saab 340 crew made a broadcast that they were clear of the preferred runway (Figure 2, position C, Saab 340). The PA-28 instructor then broadcast their ‘rolling call’ (Figure 2, position C, PA-28) and commenced take-off at 1620:07. 

At 1620:25, the Dash 8 crew gave an entering call for runway 05 with intentions to taxi to taxiway C (Figure 2, position C, Dash 8) and then entered the runway.

On hearing the Dash 8 crew’s broadcast, the Saab 340 crew notified the Dash 8 that ‘there is an aircraft taking off on runway 23’ at 1620:33. Simultaneously, the PA-28 student pilot also rejected their take-off. 

The Dash 8 crew immediately stopped at their current position, with the aircraft still perpendicular with the runway and estimated by the captain to be about 5 m inside the runway gable markers.[2] The captain acknowledged the broadcast and then visually identified the PA-28 on the runway. 

The captain of the Dash 8 subsequently engaged Beta plus power mode[3] (reverse thrust) to reverse the Dash 8 backwards along taxiway B to ensure clearance of the preferred runway. The PA-28 crew broadcast they would exit runway 23 on taxiway D.

The Dash 8 captain then established direct radio contact with the PA-28 crew, stating ‘nil radio transmission heard and they are still broken’.

The PA-28 vacated the runway and taxied again for a subsequent departure. The Dash 8 then re-entered runway 05 and backtracked runway 23 and vacated to the apron.

Context

Pilot information

Flight crew VH-QOD (Dash 8)

The captain held an Air Transport Pilot Licence (Aeroplane) and a valid class 1 aviation medical certificate. They reported a total flying time of 2,912 hours with 2,389 of those being on the Dash 8 aircraft type. The captain reported being familiar with Wagga Wagga Airport and had operated there regularly. 

The first officer (FO) held a Commercial Pilot Licence (Aeroplane) (CPL-A) and a valid class 1 aviation medical certificate. They reported a total flying time of 1,312 hours with about 438 of those hours being on the Dash 8. The FO had been employed with the operator for approximately a year and had flown into Wagga Wagga Airport during their training and subsequent line operations.

Flight crew VH-XDK (Piper PA-28)

The instructor of the PA-28 held a CPL (Aeroplane) with a grade 2 instructor rating. They held a valid class 1 aviation medical certificate and reported a total flying time of 796 hours, with approximately 146 hours being on the PA-28. The instructor regularly operated out of Wagga Wagga Airport, as it was the company base of operation. 

The student pilot of the PA-28 held a class 1 aviation medical certificate and reported about 17 hours of flying time.

Aircraft information 

VH-QOD (Dash 8)

The De Havilland Aircraft of Canada Limited (DHC) DHC-8-402, was a high-wing, pressurised, commuter aircraft powered by 2 turboprop engines. VH-QOD was manufactured in Canada in 2006 and was first registered in Australia on 22 May 2006.

VHF radio antenna position and condition

The Dash 8 had 2 VHF radio systems, each using separate antennas installed on the upper and lower fuselage (Figure 3): 

• Number 1 VHF COM antenna (VHF COM 1) mounted on the roof of the aircraft forward of the wings.
• Number 2 VHF COM antenna (VHF COM 2) mounted on the belly of the aircraft.

Figure 3: Dash 8 with annotations of VHF antenna locations on airframe

Source: Gyo Kamata Jetphotos.com, annotated by the ATSB

Transponder and ADS-B system on the Dash 8

The Dash 8 was equipped with an automatic dependent surveillance-broadcast ADS-B mode S transponder. ADS-B uses digital positional data provided by a GPS sensor on board the aircraft. This information is transmitted via the same channels used in conventional aircraft transponder transmissions. The Dash 8, ADS-B transponder units are fully integrated through the Dash 8 audio and radio control and display unit. Positional data for each ADS-B transponder is provided through the aircraft flight management system.

TCAS system on the Dash 8

A traffic collision avoidance system (TCAS) was fitted to the Dash 8. A TCAS interrogates the transponders of nearby aircraft and uses this information to calculate the relative range and direction of this traffic. The system displays this information to the flight crew, providing situational awareness of the location of other aircraft, and is available on the ground and when airborne. 

TCAS is designed to be used as an airborne device, which performs surveillance of nearby aircraft and provides information on the relative direction and altitude of these aircraft so that the collision avoidance algorithms can perform their function (Federal Aviation Administration, 2011) 

Limitations exist for the use of TCAS in lateral separation. Current generations of TCAS are primarily focused on vertical separation (climb or descent); TCAS I and II generations of TCAS do not provide horizontal separation.

In certain circumstances functions and alerts within the TCAS system are inhibited. An example is documented in FAA AC 90-120 (Federal Aviation Administration, 2024) that noted:

2.11.5 ACAS[4] does not display aircraft on the ground and may not display an aircraft when own-ship ACAS estimates that the other aircraft is below 380 feet Above Ground Level (AGL), unless the other aircraft is operating with a Mode S transponder that reports airborne status.

While the use of TCAS for monitoring other aircraft on the ground was not an operator procedure, the Dash 8 crew identified that they regularly used it as an aid for situational awareness. The captain and FO both recalled reviewing their TCAS with only one aircraft (the Saab 340) being seen. 

Flightradar24 application 

The crew of the Dash 8 utilised an electronic flight bag (EFB).[5] Additionally during taxi, they reviewed the Flightradar24 application as a tool to enhance their situational awareness of potential traffic in the area. 

Flightradar24 is a global flight tracker that shows live air traffic from around the world and combines data from several sources including ADS-B. 

QantasLink did not have a formal policy referring to the use of the Flightradar24 application. However, the flight crew advised that this application is often used by pilots as a resource to aid situational awareness. As with TCAS, only the Saab 340 aircraft was visible on the Flightradar24 app during the Dash 8 taxi period.

VH-XDK (Piper PA-28)

VH-XDK was a Piper Aircraft Corporation, PA-28-161 Cherokee Warrior III, manufactured in the US in 2008. VH-XDK was a single‑engine, 4‑seat, low‑wing design aircraft, operated by Australian Airline Pilot Academy Pty Ltd (AAPA).

VHF radio systems on PA-28

The aircraft was equipped with 2 Garmin G430[6] VHF navigation/communication systems, transmitting at a minimum of 10 watts through 2 independent antennas. The VHF COM 2 antenna is located on the top of the fuselage and the VHF COM 1 antenna is located on the underside of the fuselage.

Figure 4: Antenna location on PA-28

Source: PA-28 operator 

Transponder and ADSB system PA-28 

The PA-28 was fitted with a Garmin GTX 330ES MODE-S, providing a mode S digital transponder signal. The transponder likely would have made the PA-28 electronically conspicuous to the Dash 8 crew through the flight crew’s Flightradar24 application on their EFBs, when selected to ON/ALT.

Meteorological information

Weather conditions at Wagga Wagga Airport around the time of the occurrence were identified as a moderate north-westerly wind at about 13 kt, with greater than 10 km visibility. The cloud was reported as broken (between 5–7 oktas[7]) between 2,000 ft and 2,600 ft above ground level.

Airport information

Wagga Wagga Airport

Wagga Wagga Airport is a regional, certified aerodrome, located about 6 NM to the south‑east of Wagga Wagga township in New South Wales, Australia. The aerodrome had an elevation of 724 ft (221 m) above mean sea level (AMSL), and had 2 runways running north‑east, south-west and north-west, south-east. The primary sealed runway at Wagga Wagga is runway 05/23 and is 1,770 m long with the secondary, unsealed runway 12/30 being 851 m long (Figure 5). 

Runway 05/23 exhibited a minor elevation differential between each runway threshold. The threshold of runway 05 was recorded at 216 m AMSL while the threshold of runway 23 was slightly lower at 214 m AMSL, resulting in a 2 m downward gradient from runway 05 to runway 23. Approximately 300 m from the runway 05 threshold, the elevation increased to 217.5 m AMSL, a rise of 1.5 m, before gradually declining towards the runway 23 threshold. This subtle elevation change created a minor undulation in the runway profile. 

Figure 5: Wagga Wagga Airport layout

Source: En Route Supplement Australia (ERSA). Airservices Australia, annotated by the ATSB

Airspace

Wagga Wagga Airport was located within non-controlled Class G[8] airspace which was available for use by aircraft operating under visual flight rules (VFR) and instrument flight rules (IFR). 

No air traffic control separation service was provided between aircraft operating in this airspace. Pilots are responsible for making themselves aware of nearby aircraft and maintaining mutual self‑separation. The primary method of traffic separation at Wagga Wagga Airport was by VHF communications coupled with visual reference, and relied on pilots using ‘alerted see-and-avoid’[9] practices (see See-and-avoid).

The Wagga Wagga CTAF operated on the VHF radio band and required pilots to monitor and make some positional broadcasts when operating within the vicinity of the aerodrome, or within 10 NM.

Reported radio dead spot

The Australian Airline Pilot Academy (AAPA) had issued an internal notice to all crew (NOTAC) on 23 August 2023, advising of a potential radio ‘deadspot’ on Wagga Wagga Airport. The NOTAC detailed:

NOTAC 032/17 CURRENT 23 08 1100 LST - Until Removed To: All Pilots 

POTENTIAL RADIO DEADSPOT ON WAGGA AIRPORT 

There is an identified radio dead spot on Taxiway Alpha between taxiway Charlie and the runway 23 holding point, prior to entering Runway 23, crew must visually check that no aircraft are entering the runway from taxiway Charlie. 

Authority: Chief Pilot.

Prior to the occurrence, the aerodrome operator had identified that ground-based vehicle radio communications were observed to have reduced effectiveness in some circumstances, however no further testing was carried out.

Radio signal transmission reception

The ATSB conducted an analysis to determine whether the radio line of sight (LOS) between the 2 aircraft, positioned at opposite ends of the runway, was obstructed by the terrain elevation at approximately 300 m down runway 05.

Firstly, a geometric LOS analysis was conducted. The analysis utilised a strict geometric LOS model, assuming a direct, unobstructed path between the transmitter and receiver, as described in standard International Telecommunications Union (ITU-R) (2019) radio propagation principles (Parsons, 2000). The results determined that the terrain elevation created a physical obstruction, blocking the direct radio LOS between the aircraft.

To assess the potential for radio communication despite the LOS obstruction, diffraction[10] effects were evaluated. The inclusion of diffraction effects was used as radio waves, particularly in the very high frequency (VHF) band used in aviation, can propagate beyond geometric LOS by bending around obstacles such as terrain features  (Rappaport, 2002). This phenomenon enables communication in scenarios where direct LOS is obstructed.

A knife-edge diffraction model was used to estimate the signal loss caused by the terrain. This model, a standard method in radio wave propagation analysis, approximates the terrain feature as a sharp, idealised edge obstructing the radio wave path (International Telecommunications Union (ITU-R), 2019). The knife-edge model was selected due to its applicability for analysing diffraction over a single, well-defined obstacle and its computational simplicity for VHF frequency analysis.

The calculations were completed using the Wagga Wagga CTAF frequency of 118.2 MHz and assumed values derived from generic radio and antenna specifications. 

Results indicated that despite the geometric LOS obstruction caused by the terrain, communication between the 2 aircraft was feasible[11] due to diffraction effects. 

A similar calculation was conducted between taxiway C and taxiway A5. It indicated that communication between 2 aircraft was also feasible. The calculated signal strength indicated that a radio transmission should have theoretically been received clearly. 

All calculations regarding VHF line of sight communication were theoretical and assumed idealised conditions. Noting the advice by AAPA of a potential radio dead spot on the airport, it should be noted that this observed dead spot may result from real-world environmental factors such as localised interference or other unmodeled conditions like vegetation or temporary obstacles, which cannot be fully replicated in theoretical calculations.

Visibility between opposite runway thresholds

A clear line of visual (eye level) sight existed between the taxiway B holding point at the threshold of runway 05 and the threshold of runway 23 (Figure 6). The pilot of the PA-28 reported they could clearly see the Dash 8 at the threshold of runway 05, as the Saab 340 vacated the runway, prior to them commencing take-off. The crew of the Dash 8 reported being able to see the Saab 340 land and vacate the runway, but did not visually detect the PA-28 prior to entering the preferred runway. After they were notified by the Saab 340, the captain and first officer were able to visually identify the PA-28 on runway 23 which was at that stage moving towards the Dash 8 on its take-off roll. 

Both the FO and the captain commented during interview of a possible obstruction to their line of sight from the PAPI[12] installation. The PAPI installation is positioned to the left of runway 05. The orientation was to the left of the Dash 8 when the aircraft was holding on taxiway B, prior to entering runway 05. PAPI units must be no more than 0.9 m above ground level. 

Figure 6: View from ground level, threshold runway 05

Source: airport operator, annotated by the ATSB 

It was noted that the visual range from holding point B to the threshold of runway 23 is greater than 1,700 m over undulating terrain, with the PA-28 presenting a small target for visual identification by the Dash 8 crew. 

ATSB calculations indicate there was a clear line of sight between the eye height of the Dash 8 crew and the eye height of the PA-28 crew. The visual line of sight between both aircraft was about 1.7 m above the geographical terrain undulations between the thresholds of runways 05 and 23. 

Human performance limitations

Object perception

There are limitations to the size of objects that are perceptible at a distance. The ATSB considered whether the crew of the Dash 8 could have been able to detect there was a small aircraft (PA-28) at the threshold of runway 23 when the Dash 8 was at taxiway B at the runway 05 end, based on the known limitations of distant object perception. It was reported by the PA-28 pilots that the Dash 8 was visible to them when they were lined up for take-off once the Saab 340 cleared the runway. However, the Dash 8 is a larger aircraft and was side-on to the PA-28 pilots at this point, and they were alerted to the Dash 8’s presence through broadcasts, however this does not mean that the Dash 8 crew could identify the PA‑28.

The 3 main factors that would affect the visual image size of the PA-28 aircraft in the Dash 8 pilot’s eye are: 

• the dimensions of the aircraft
• its relative orientation
• distance from the viewer. 

Past research (Hobbs, 2004) has shown distant objects can be seen when their visual angle is at least 24−36 minutes of arc (0.4−0.6°), and down to a minimum of 12 minutes of arc (0.2°) in ideal viewing conditions (ATSB, 2025).

Once the Saab 340 had cleared the runway and the visual path to the PA-28 was clear for the Dash 8 crew, the PA-28 was lined up for take-off. When lined up on the runway, the most prominent part of the PA-28 was the fuselage, which was 1.65 m high, with a wingspan of 10.79 m (noting that the wings would be edge-on). At the distance of 1,700 m, this would have presented a visual image that was about 3 minutes of arc (0.06°).[13] Additionally, as the PA-28 was moving down the runway, the gradual change in angular size would likely have been virtually imperceptible due to the eye’s limited sensitivity to small angular variations. Therefore, in the absence of confounding factors, it would have been very unlikely that the PA-28 would have been detectable by the Dash 8 pilots at that distance.    

Other factors can also exist that can affect whether a pilot will be able to see another aircraft, including the background that an object is seen against. As can be seen in Figure 6, the background behind the runway 23 threshold was dark and would have provided good contrast to the white PA-28 aircraft, making detection easier.

Finally, the use of lights by the PA-28 would have enhanced detection. Strobe lights would have enhanced detection though flash and movement. However, landing lights are angled forward and downwards, and may not have been as detectable by the Dash 8 crew.

See-and-avoid 

At and around non-controlled aerodromes, pilots are responsible for making themselves aware of nearby aircraft and maintaining separation. Safe operations at non-controlled aerodromes rely on all pilots maintaining an awareness of their surroundings and other aircraft, the principle of ‘see‑and‑avoid’. 

A visual traffic search in the absence of specific traffic information is less likely to be successful than a search where traffic information has been provided. Knowing where to look can greatly increase the chance of sighting the traffic.

An ‘unalerted’ search is one where reliance is entirely on the pilot searching for, and sighting, another aircraft without prior knowledge of its presence. An ‘alerted’ search is one where the pilot is alerted to another aircraft’s presence, typically through radio communications or aircraft-based alerting systems. An alerted search supports a pilot’s situational awareness and enhances their visual lookout for traffic by developing an expectation of visually acquiring the traffic in a particular area.

Issues associated with unalerted see-and-avoid have been detailed in the ATSB research report, Limitations of the See-and-Avoid Principles(Hobbs, 2004). The report highlights that unalerted see-and-avoid relies entirely on the pilot’s ability to sight other aircraft. 

Tools to enable ‘alerted see-and-avoid’ include:

• VHF radio
• transponders, used by traffic collision avoidance system (TCAS)
• automatic dependent surveillance broadcast (ADS-B)
• electronic flight bag (EFB) applications 

Hobbs (2004) identified that an alerted search is likely to be 8 times more effective than an unalerted search, this highlighted that knowing where to look greatly increases the chances of sighting other traffic.

Alerted see-and-avoid relies on pilot or crew awareness of all traffic in their vicinity, especially those that may be considered a hazard to their operations. Enhanced situational awareness requires the pilot or crew mental model of the location and intentions of nearby traffic to be updated regularly to form an evolving understanding of the nearby traffic. Without this information, the likelihood of effective situational awareness is degraded, and the mental model and shared understanding of hazards is compromised.

Operational procedures

QantasLink Dash 8 procedures

Non-controlled aerodrome VHF radio procedure

The QantasLink Dash 8 standard operating procedure for departure from a non‑controlled aerodrome (such as Wagga Wagga Airport), at the time of the occurrence, required VHF COM 1 to be set to the area frequency and VHF COM 2 to be set to the CTAF, as passenger boarding commenced. 

Prior to releasing the handbrake to taxi, a call was to be made to the relevant air traffic centre on VHF COM 1 and then followed by a taxi call to the CTAF on VHF COM 2. However, due to this being a repositioning flight, the crew only broadcast on VHF COM 2 on the CTAF frequency.

Controlled aerodrome VHF radio procedure

The QantasLink Dash 8 standard operating procedure for departure from a controlled aerodrome, at the time of the occurrence, required VHF COM 1 to be set to the primary air traffic control frequency for ground and air-based communications. The VHF COM 2 was set for other communications (such as ATIS,[14] AWIS,[15] PAL and CTAF). 

Reverse thrust on the ground

QantasLink policy for engaging reverse thrust during ground operations required prior approval from the Head of Flight Operations. This approval requirement was due to the risks associated with not being able to confirm clearance from other traffic or obstacles that cannot be visually identified from the flight deck. The captain advised during interview that they were aware of this policy.

Procedures for transponder use

The QantasLink procedure was to set the transponder to ‘ON/ALT’ with the applicable transponder code[16] as part of the pre-flight process. This is achieved either after obtaining airways clearance or (at airports where airways clearance is not obtained until after take-off), as part of the pre‑flight process before engine start.

AAPA PA-28 operator procedures

VHF radio procedure

The AAPA procedures, contained within the ‘Piper Warrior III Crew Operating Manual’, normal procedures, required COM 1 to be selected to the local area frequency, tower, ground, clearance delivery, approach or departure frequency as required. COM 2 was required to be set to the CTAF, ATIS, AWIS, MULTICOM or guard frequency (121.5 MHz) as required.

The instructor confirmed during interview that, at the time of the occurrence, COM 1 was set to Melbourne Centre (area frequency) and COM 2 was set to the Wagga Wagga CTAF.

Procedures for transponder use

The PA-28 operator’s’ procedure for transponder operation was to set the applicable transponder code and select the STBY[17] function during taxi. Prior to entering the runway, ON/ALT mode[18] was to be selected.

The PA-28 operator’s training manual notes:

All pilots must ensure ALT is selected on the transponder during the LINE UP CHECKLIST. Other aircraft equipped with TCAS rely on transponder information for pilot alerting and collision avoidance functions.

PA-28 external light use

The PA-28 operator’s procedure for the selection of external lights is documented in its Piper Warrior III flight crew operating manual, normal procedures. 

As required by the ‘pre line up scan action flow’, the pilot selects the landing lights ‘on’ (during daytime operations), immediately prior to commencing a take-off roll at a non‑controlled aerodrome. 

The instructor recalled that normal behaviour would involve the pilot selecting the landing lights ‘on’, when the ‘rolling call was issued’.  

Regulations regarding transponder use

The use of surveillance equipment such as ADS-B and transponder is outlined in the Civil Aviation Safety Regulations Part 91 Manual of Standards (MOS) and the Airservices Australia Aeronautical Information Publication (AIP).

Chapter 26 of the Part 91 MOS, operation of surveillance equipment – general requirements stated, among other things, that transponder equipment required to be fitted and carried on an aircraft must be continuously operated. It also identified that ‘continuous operation’ for a transponder means that the equipment must be operated in a mode that enables a secondary surveillance radar (SSR)[19] response to be transmitted and, where an altitude reporting capability is available, that this capability is also activated.

AIP Australia ENR 1.6 paragraph 7.1.9 stated:

A pilot operating a Mode S transponder must:

b. On receipt of ATC clearance, or requesting the earlier of Push Back or Taxi, select TA/RA/XPDR/ ON AUTO as applicable. 

CASA advised that item ‘b’ only applies at controlled aerodromes. At non-controlled aerodromes, transponders must be turned on prior to becoming airborne.

Radio communication

VHF radio is the primary communication tool commonly used to provide ‘alerted see‑and‑avoid’ from sport and recreational private flying to air transport. Broadcasts on the CTAF to any other traffic in the vicinity of a non-controlled aerodrome are made to provide situational awareness, traffic separation and deconfliction to other traffic in the vicinity.

Positional broadcasts

Civil Aviation Safety Regulation 91.630 made certain radio calls mandatory for aircraft that are fitted with or carry a VHF radio. Chapter 21 of the Part 91 Manual of Standards (MOS) prescribed one type of mandatory broadcast that applies at all non-controlled aerodromes, namely:

When the pilot in command considers it reasonably necessary to broadcast to avoid the risk of a collision with another aircraft.

To aid in increasing situational awareness at non-controlled aerodromes, recommended broadcasts are published by the Civil Aviation Safety Authority (CASA). These broadcasts enable pilots to alert other traffic to their location and intentions before take‑off, inbound to land at, or if intending to overfly a non-controlled aerodrome. 

Standardised radio transmissions and phraseology assist with effective and efficient radio communication. To achieve this, the application of recommended positional broadcasts (Table 1) for VFR traffic are published in CASA Advisory Circular (AC) 91-10, Operations in the vicinity of non-controlled aerodromes. 

Table 1: Recommended positional broadcasts in the vicinity of a non-controlled aerodrome

Source: CASA AC 91-10 Operations in the vicinity of non-controlled aerodromes

Limitations of positional broadcasts

Positional broadcasts are a one-way communication and do not imply receipt of information by other parties unless direct radio contact is made between stations. 

Positional broadcasts rely on the accuracy of the information being broadcast and the ability of other traffic receiving, comprehending and reacting to this information. 

CASA AC 91-10 stated: 

8.2.1 Pilots are reminded that although correct and informative radio calls play a critical role in ensuring collision avoidance in uncontrolled airspace, to ensure the safety of their aircraft they cannot assume that an absence of other radio calls means there are no nearby or conflicting aircraft. 

8.2.2 Pilots must continually look out for other aircraft, even when their broadcasts have generated no response

8.2.3 Accidents and incidents have occurred where pilots incorrectly assessed the threat posed by another aircraft, either due to the pilot incorrectly assessing the relative aircraft flight paths, or inaccurate information being provided by other pilots.

Dash 8 radio reception and transmission

Two Dash 8 ground communication events has been previously identified by ATSB investigations (AO-2023-025 and AO-2023-050) at Mildura Airport (see Related occurrences).

These 2 events resulted in the second investigation testing the Dash 8’s VHF systems. The testing was conducted by the ATSB, the Australian Media and Communications Authority[20] and QantasLink. The testing measured the transmission power pattern of the Dash 8’s 2 communication systems (upper and lower antennae), when the aircraft was on the ground at Mildura Airport.

The testing identified that ground‑based Dash 8 signal strength reception could be adversely affected by the aircraft’s orientation relative to the other aircraft or antenna locations. Additionally, the average signal strength forward of the aircraft was 8.5 dBm[21] stronger than the average signal strength behind and to the side of the aircraft. A significant recorded signal strength and clarity reduction on both VHF COM 1 and VHF COM 2 radios was observed when the tail of the Dash 8 was pointed towards the receiver.

It was further identified that reception and transmission on VHF COM 2 on the ground (via the lower antenna, as used for QantasLink Dash 8 ground communications at non‑controlled aerodromes) had significantly reduced strength and clarity compared to VHF COM 1.

The Dash 8 manufacturer, De Havilland Aircraft of Canada Limited, advised that VHF COM 1 was expected to provide more reliable performance in ground-based communication with other ground stations. 

Two flight operations service letters (Appendix B – Flight Operations Service Letters) were released on 6 December 2024 for the Dash 8-100/200/300 (DH8-SL-23-008A) and Dash 8‑400 (DH8-SL-23-020A). Details included a description of the limitations of VHF line of sight communications and the recommendation that VHF COM 1 may provide a better signal (receiving and transmitting) to other stations on the ground, or nearby in the air. 

As a result of the first occurrence at Mildura on 6 June 2023 (see ATSB investigation report AO-2023-025), QantasLink issued a technical advisory bulletin, effective from 17 July 2024, which changed the VHF communications procedure for Mildura departures. The aim of the change was to improve ground-to-ground CTAF VHF communication during the taxi phase. However, this has only been adopted at Mildura Airport through a route manual amendment (now company port supplement) and does not provide any effective level of mitigation to this known risk for other non-controlled aerodromes. 

Related occurrences

ATSB investigation (AO-2023-025)

On 6 June 2023, a Piper PA-28-161, taxied for runway 36 at Mildura Airport, Victoria. At about the same time, a QantasLink De Havilland Aircraft of Canada Limited DHC-8-315 (Dash 8) began to taxi for runway 09. Both aircraft broadcast their intentions on the local common traffic advisory frequency. The pilot of the PA-28 was aware of the Dash 8, but the crew of the Dash 8 were not aware of the PA-28. Both aircraft commenced their take‑off at about the same time and the Dash 8 crossed ahead of the PA-28 at the runway intersection of 09/36 by about 600 m. 

The pilot of the PA-28 was unable to visually sight the location of the Dash 8 due to airport buildings and assumed that the Dash 8 was still backtracking on runway 09. They did not directly contact the Dash 8 to positively organise separation. They also incorrectly referred to the runway direction at Mildura Airport as ‘runway 35’ instead of ‘runway 36’. 

The Dash 8 crew was focused on obtaining their pre-departure information from air traffic control and had the volume for the radio tuned to the common traffic advisory frequency turned down. An over transmission from air traffic control meant that the Dash 8 crew only received certain elements of the PA-28 pilot’s radio calls. This likely led to an incomplete comprehension of traffic by the Dash 8 crew who believed that the PA-28 was not at Mildura (due to the incorrect reference to runway 35). However, they did not seek further information of the source of the radio calls to positively identify the traffic location.

The investigation found that, due to the topography and buildings at Mildura Airport, aircraft are not directly visible to each other on the threshold of runways 09, 27 and 36. The Dash 8 crew did not give a rolling call on runway 09, nor were they required to. The lack of a requirement for mandatory rolling calls increased the risk of aircraft not being aware of each other immediately prior to take-off.

ATSB investigation (AO-2023-050)

On 29 September 2023, De Havilland Aircraft of Canada Limited DHC-8-315 (Dash 8), taxied for runway 09 at Mildura, Victoria. A short time later, an amateur‑built Lancair Super ES aircraft taxied for runway 36 at Mildura, for a private flight to Ballarat. 

Both aircraft gave taxi, entering and backtracking calls on the local common traffic advisory frequency. Neither the pilot of the Lancair, nor the crew of the Dash 8, were aware of each other. The crew of the Dash 8 gave a rolling call and had commenced their take-off on runway 09 as the pilot of the Lancair gave a rolling call on runway 36, this was received by the Dash 8 crew with an immediate response given to the Lancair to hold on the runway. Another aircraft, taxiing behind the Lancair for runway 36, advised them to hold position while the Dash 8 departed.

The Dash 8 crossed the runway 09/36 intersection while the Lancair remained on the threshold of runway 36.

The investigation found that, due to the topography and buildings at Mildura Airport, aircraft are not directly visible to each other on the threshold of runways 09, 27 and 36. It was also identified that the crew of the Dash 8 were actively engaged in in organising separation with other airborne traffic and the Lancair’s entering and backtracking call was over transmitted. 

It was also identified that the Dash 8 had reduced ground-based radio reception and transmission strength and clarity on VHF COM 2 (which used an antenna on the aircraft underbelly) and was required to be used by company procedures. The investigation also found that the Dash 8 had reduced radio reception and transmission strength to and from other airfield users located behind the Dash 8 which affected radio call readability.

This led to a situation where the crew of the Dash 8 had an incomplete comprehension of the ground-based traffic at Mildura, and had no knowledge of the Lancair until during the take-off. In addition, due to the position and distance of the Dash 8, the pilot of the Lancair had no awareness of the Dash 8 until another aircraft advised that the Dash 8 was rolling on runway 09.

ATSB investigation (AO-2024-009)

On 19 March 2024, a Fairchild SA226-TC (Metroliner), taxied at Geraldton, Western Australia, for runway 03. About one minute later, a Beechcraft A36 (Bonanza), taxied for runway 14. After reaching their respective runway thresholds, both pilots attempted to contact the other, however, they did not hear each other, nor could they see each other. A third aircraft assisted by relaying information. Based on the information received, the Bonanza and Metroliner pilots commenced their take-off within 3 seconds of each other. The Metroliner crossed runway 14 about 400 m in front of the Bonanza, with a vertical separation of about 250–300 ft. 

The investigation found that, when aircraft were positioned at the thresholds of runway 03 and 14 (and 08), they will unlikely be visible to each other due to the position of the airport buildings. Further, they may not be contactable on VHF radio due to potential shielding effects. This resulted in the pilots being unable to verify each other’s position and intentions prior to commencing their take-off. 

While the pilot of the third aircraft was attempting to assist, the details provided were inaccurate and incomplete. This inadvertently resulted in misinterpretation by the Bonanza and Metroliner pilots and influenced their decision to take off.

Safety analysis

Introduction

On 15 July 2024, a QantasLink De Havilland Aircraft of Canada Limited DHC-8-402, registered VH-QOD, entered runway 05 at Wagga Wagga Airport, unaware that a Piper PA-28, registered VH-XDK, was commencing its take-off roll from runway 23. 

While the crew of the Dash 8 was entering the runway, the crew of a third aircraft (Saab 340), notified the Dash 8 crew of the PA-28’s presence. 

Once the Dash 8 crew was aware of the PA-28, the captain stopped the aircraft about 5 m past the holding point, then engaged ‘reverse thrust’ to back the Dash 8 clear of the runway. Concurrently, the pilot of the PA-28 rejected their take-off from runway 23. 

This analysis will explore operational considerations such as situational awareness, the breakdown of communication, shared mental model and alerted see‑and‑avoid, as well as the limitations identified within operational procedures and specific aircraft system limitations.

Situational awareness and communication 

The PA-28 crew was aware of the Dash 8 intentions and location. The PA-28 instructor subsequently held the assumption that the Dash 8 crew had, likewise, received their radio broadcasts and were aware of the PA-28’s location and intentions for take-off. 

The Dash 8 crew did not expect any other traffic, in addition to the Saab 340. The Dash 8 crew reported not identifying the PA-28 either visually or via electronic means, nor hearing the PA-28’s radio communications. During taxi to the opposite end of the runway, the Dash 8 was pointing in the opposite direction to the PA-28, and later the line of sight to the PA-28 would have been obscured by the landing Saab 340. As the PA-28 transponder was not turned on prior to entering the runway, it was not identifiable electronically either prior to this time. The remaining opportunity to increase situational awareness was the initial taxiing radio calls. The Dash 8 crew’s broadcast immediately after they were told about the conflicting traffic shows they were surprised to learn there was another aircraft operating from the airport, this suggests that the Dash 8 crew members did not hear these transmissions rather than forgot them.

Communication

Succinct and timely radio communication is important to ensure high levels of situational awareness and aids in providing alerted see-and-avoid safety outcomes. As such, the accuracy of the information broadcast by pilots is critical in ensuring minimum misunderstanding.

Common traffic advisory frequency (CTAF) recordings indicated that the PA-28 pilot made the recommended positional broadcasts in preparation for their departure – a taxi call when leaving the apron area, entering the runway and then a rolling call on the runway. However, positional broadcasts are ‘one-way’ communications by nature and do not explicitly mean that other traffic in the vicinity interpret and understand the intended information. 

The PA-28 instructor reported that they believed that the Dash 8 crew had received and understood their broadcasts. This misunderstanding was based on the presumption that because the PA-28 could hear the radio calls and see the Dash 8, that the Dash 8 crew also could hear the radio calls and see the PA-28.

The PA-28 crew could hear the communications between the Dash 8 and Saab 340, centring on the Dash 8 crew ensuring they did not impede the Saab 340’s landing. However, the PA-28 instructor expected that the Dash 8 would hold short of the runway to allow them to take-off without hearing any broadcasts to that effect. As a result, the PA-28 crew did not initiate any direct radio contact with the Dash 8 crew to clarify their intentions. 

Had the PA-28 instructor attempted to make direct contact with the Dash 8, and not been successful, they would have subsequently realised there had been a communication breakdown. 

Visual identification 

The topography at the aerodrome results in a runway height change between the thresholds of runway 05/23 at Wagga Wagga Airport. This change is up to 2 m in elevation between the thresholds, with a slight hump towards the runway 05 end. However, there was a clear visual line of sight from one threshold to the other.

When the Dash 8 was on taxiway B at the holding point of the runway, the crew’s vision of the PA-28 may have been blocked by the landing Saab 340. By the time that aircraft cleared the runway, the PA-28 was lined up on the runway and had started its take-off roll. 

Based on the limitations of vision, it is very unlikely that the Dash 8 crew would have been able to detect the presence of the PA-28 about 1,700 m away, simply by looking in that direction, as the image of that aircraft would have been too small for detection. The use of landing and strobe lights would have assisted, but over that distance would have been limited. Consequently, the Dash 8 crew, who reported looking before entering the runway, did not detect its presence.

If the Dash 8 crew had previously been alerted to the presence of another aircraft, this would have increased the chance of detection. Alerted see‑and‑avoid means that the presence and approximate location of another aircraft is known or expected, allowing the crew to narrow their visual search. However, in this case, the absence of the Dash 8 crew detecting radio calls from the PA-28 and no other aircraft identified during taxi either visually or electronically, meant that the Dash 8 crew held an expectation that there were no other ground-based aircraft operating at the airport at that time. Not detecting the PA‑28 was consistent with that expectation.

The ATSB identified that while the PA-28 crew conducted their taxi, engine run-ups and aircraft checks, their transponder was set to standby. Prior to entering the runway for take-off, the pilot of the PA-28 then switched the transponder from standby to ‘ON’. 

The Dash 8 crew reported that electronic surveillance equipment was used as an aid to supplement the identification of potential conflicting traffic in the vicinity of a non‑controlled aerodrome prior to take-off. Both the captain and first officer of the Dash 8 recalled conducting a check of their onboard surveillance systems (electronic flight bag, traffic collision avoidance system (TCAS) aircraft display and Flightradar24 application) during taxi and did not identify any traffic other than the third-party landing aircraft.

Non-active mode S transponders do not provide electronic surveillance information to other aircraft. If the transponder is not selected ‘on’, a missed opportunity exists to provide situational awareness to other aircraft. 

It is likely, had the PA-28 mode S transponder been activated at the first aircraft movement for taxi, the flight crew of the Dash 8 would have detected the presence of the PA-28 and developed an expectation of its location and potential confliction. This would have prompted the crew to coordinate both verbally and aided alerted see‑and‑avoid.

Australian Airline Pilot Academy procedures for transponder

The AAPA’s manual had a procedure that prescribed the use of the transponder on standby during startup and taxi, with a requirement to only switch it to ‘ALT’ prior to entering the runway. 

Widespread use of surveillance equipment, such as transponders with ADS-B installed, offer significant improvement to allow pilots to be more certain of the location of traffic, particularly outside controlled airspace environments. 

Had the PA-28 crew been required to select their mode S transponder to ‘ON/ALT’ prior to initial taxi, this would have made them electronically visible to the Dash 8 crew who reported actively seeking this information. 

Topographic shielding 

Local operators at Wagga Wagga Airport have observed and reported that a reduction in effectiveness of VHF communications had been experienced at certain locations on the airport. This observation of topographical radio shielding was identified by multiple parties. 

Topographic changes exist in and around Wagga Wagga Airport and were suggested by stakeholders to result in varying levels of topographical radio shielding at the eastern end of taxiway A and the end of runway 23. 

Prior to the occurrence, the PA-28 operator issued internal notifications of an ‘identified radio dead spot’, to its flight crews.  

Operator advice and reported experience regarding topographical shielding at Wagga Wagga Airport was documented procedurally for AAPA, but was not available to Dash 8 crew operating into Wagga Wagga Airport. The ATSB did not independently confirm the existence of radio shielding. Operator experience and local procedure indicates this is likely an ongoing issue at Wagga Wagga Airport.

Dash 8 radio reception and transmission

VHF radio transmissions facilitate exchanges between air traffic control, aircraft, and emergency services. These signals primarily rely on line of sight propagation, requiring an unobstructed path between the transmitting and receiving antennas. When line of sight is obstructed by terrain features, aircraft structure, or by man-made structures like buildings, VHF signals can be significantly attenuated, leading to reduced communication range, signal distortion, or complete loss of contact. However, under certain conditions, VHF signals may propagate beyond line of sight through mechanisms such as reflection and diffraction. While these phenomena can marginally extend communication range, their effectiveness is highly dependent on the environment.

Previous analysis of Dash 8 ground-based communications (AO-2023-050) identified a significant reduction in radio signal strength and readability when using the VHF COM 2 antenna for ground operations. The analysis determined that the aircraft structure and surrounding airport infrastructure at Mildura Airport impeded VHF COM 2 signal transmission and reception, limiting its effectiveness. In contrast, using the VHF COM 1 antenna provided a clearer line of sight to ground-based stations, resulting in more reliable communication.

ATSB analysis of the radio communications between the Dash 8, the Saab 340, and the PA-28 identified that the Dash 8 crew, while using VHF COM 2, could hear and respond to the Saab 340, likely due to its proximity to the aircraft. However, they could not hear the PA-28. 

Their inability to hear the PA-28 was likely due to previously identified issues with the VHF COM 2 antenna and the addition of runway undulations which further obstructed the line of sight between the Dash 8’s VHF COM 2 antenna and the PA-28. This likely exacerbated the antenna’s limitations and hindered effective signal propagation.

Qantas procedures for VHF

QantasLink procedures required the use of VHF COM 2 for ground-based communication at non-controlled aerodromes. However, the use of VHF COM 2 for ground-based communications was not required for controlled airspace, where ground‑based communications were conducted by VHF COM 1. 

In previous ground-based signal strength testing at Mildura Airport (see ATSB investigation report AO-2023-050), the ATSB identified a significant reduction in the Dash 8 VHF radio transmission strength and readability particularly when greater transmission and reception distances were involved. It was also found that the use of VHF COM 2 reduced ground-based transmission reception strength and clarity in comparison with VHF COM 1. 

Following a near collision occurrence at Mildura on 6 June 2023, QantasLink changed the VHF communications procedure for Mildura Airport departures. The changed procedure required use of the VHF COM 1 system, noting that this was found to have an improvement in both transmission clarity and reception. However, this has only been adopted at Mildura Airport and so does not provide any effective level of mitigation to this known risk for other non-controlled aerodromes.

Given the reported radio dead spot at Wagga Wagga Airport, the use of VHF COM 2 with the bottom‑mounted antenna by QantasLink Dash 8s likely increased the likelihood of Dash 8 crews not receiving strong and readable radio calls from other ground-based aerodrome users.

Part of the shared mental model for all operations at non-controlled aerodromes is the situational awareness of all crew, in this instance the crew of the Saab 340 identified a potential threat to the safety of the other 2 aircraft and clearly broadcasted their concern.

Crew interviews as well as CTAF recordings clearly showed that the proactive initiative of the Saab 340 crew to alert the Dash 8 crew of the presence of the PA-28 was instrumental in preventing a potential on runway collision.

After entering the preferred runway, the captain became aware of the hazard present due to the vacating third party aircraft report. The captain’s decision to apply brakes and then engage reverse thrust to clear the runway was almost certainly made to avoid the greatest perceived threat, that being, a possible collision on the runway. 

Reversing the aircraft under its own power is a non-normal manoeuvre with additional risks. As such QantasLink policy would normally require Head of Flight Operations approval to conduct the manoeuvre. 

The captain’s decision to reverse the aircraft could be attributed to the lower (perceived) risk involved with reversing the aircraft, versus the known risk of a possible collision.

The captain exercised their command authority, based on the information available, to make an assessment of the greatest threat, subsequently deciding to reverse the aircraft, without being able to positively confirm traffic and obstacle avoidance. 

Risk management focuses on reducing the potential risks associated with a decision. Thus, considering that decision‑making, when elements of uncertainty exist, focuses on making the best decision given the available information.

The pilot in command of an aircraft has the final authority over the safety of the aircraft and its occupants. When operating in dynamic environments, the pilot in command will need to consider possible outcomes and alternative courses of action to ensure clear risk-based decisions are made. In this instance the captain elected to reduce the likelihood of a catastrophic event by reversing clear of the preferred runway after having a reasonable expectation that the taxiway was clear behind the Dash 8.

Findings

From the evidence available, the following findings are made with respect to the runway incursion involving De Havilland Aircraft of Canada Limited DHC-8, VH-QOD, and Piper PA‑28, VH-XDK, at Wagga Wagga Airport, New South Wales, on 15 July 2024. 

Contributing factors

• During ground-based repositioning, the Dash 8 entered runway 05 while the PA-28 had commenced its take-off roll from runway 23. The Dash 8 crew were not aware of the PA‑28 until notified by the crew of a third aircraft of the potential conflict.
• The pilots of the PA-28 gave the recommended radio calls, however, did not directly communicate or engage with Dash 8 crew to arrange separation.
• Without any prior alert or expectation of the presence of the PA-28, the Dash 8 crew did not visually detect the PA-28 on take-off from the reciprocal end of the runway, prior to the Dash 8 entering the runway to taxi to the terminal.
• During taxi for take-off, the PA-28 was not broadcasting transponder information to identify them to other traffic in the vicinity of the aerodrome.
• The Australian Airline Pilot Academy flying school flight crew operating manual only required pilots to activate the transponder prior to entering the runway. The use of a transponder during taxi would normally provide an additional source of positional data to other pilots, aiding visual identification and alerted 'see‑and‑avoid' to other aircraft. (Safety issue)
• Reduced VHF ground-based communication was identified at the eastern end of runway 23 at Wagga Wagga Airport. Local operator reports and procedures indicate likely reduced communications on the eastern end of taxiway A to other areas on the aerodrome.
• Dash 8 ground-based transmissions on VHF COM 2 had reduced strength and clarity. This likely led to situations where other aircraft had difficulty in receiving and understanding radio transmissions, and the Dash 8 not receiving the PA-28 radio transmissions.
• QantasLink's radio procedure required crew to use communications panel radio 2 (COM 2) to broadcast and receive on local frequencies during operations at a non-controlled aerodrome. This reduced the likelihood of the Dash 8 receiving the calls from other aircraft at either end of runway 05/23 at Wagga Wagga Airport in certain circumstances. (Safety issue)

Other (key) findings

• Third party intervention by the Saab 340 crew prevented the Dash 8 from lining up on runway 05 whilst the PA-28 was engaged in the take-off roll.
• On assessing that a collision risk existed with the rolling PA-28, the captain held a reasonable expectation that it was clear and reversed the aircraft away from the preferred runway without being able to confirm that no other aircraft were behind the Dash 8.

Safety issues and actions

AAPA procedures for transponder usage

Safety issue number: AO-2024-041-SI-01

Safety issue description: The Australian Airline Pilot Academy flying school flight crew operation manual only required pilots to select ALT on the transponder, as part of the Pre Line Up Scan Action Flow and associated Checklist prior to entering the runway. The use of a transponder during taxi would normally provide an additional source of positional data to other pilots, aiding visual identification and alerted 'see‑and‑avoid' to other aircraft.

Safety advisory notice to pilots and operators of mode S transponder equipped aircraft

SAN number: AO-2024-041-SAN-01

The effective use of the mode S transponder from first movement of the aircraft can serve as an effective tool in adding another layer of collision avoidance between aircraft on the ground. Utilising the mode S transponder with ADS-B OUT enabled is the most effective way of making an aircraft electronically conspicuous and delivering maximum interoperability with other aircraft as well as the ground ATM environment. The ATSB advises pilots and operators to review their procedures to ensure that mode S transponders are on from first movement of the aircraft, particularly at non-controlled aerodromes.

QantasLink radio procedure

Safety issue number: AO-2024-041-SI-02

Safety issue description: QantasLink's radio procedure required crew to use communications panel radio 2 (COM 2) to broadcast and receive on local frequencies during operations at a non‑controlled aerodrome. This reduced the likelihood of the Dash 8 receiving the calls from other aircraft at either end of runway 05/23 at Wagga Wagga in certain circumstances.

Safety action not associated with an identified safety issue

Safety action by Wagga Wagga Airport 

After the occurrence, the aerodrome operator identified that it was possible that a radio black spot may be present based on observations of radio reception just beyond the threshold of runway 23. 

Wagga Wagga city council has issued a precautionary NOTAM after the occurrence which provides advice to all operators of possible visibility issues with aircraft on the threshold of runway 23 and the possibility of radio black spots existing under some conditions. The NOTAM note reads:

LIGHT ACFT AT THR OF RWY 23 NOT VISIBLE TO OTHER ACFT USING RWY 05. 

RADIO BLACK SPOTS MAY RESULT UNDER SOME CONDITIONS.  

Safety action by QantasLink

On 2 August 2024 QantasLink safety issued a company safety alert notice advising crew of a suspected VHF radio blackspot on taxiway A4 and A5 towards the threshold of runway 23 and other areas of the Wagga Wagga aerodrome. They issued the following advice to crew:

Whilst we investigate the issue with the aerodrome operator and other aerodrome users, we encourage crew to consider the following precautions when taxiing for departure or any other manoeuvring on the ground: 

- ensure any weak, garbled or carrier-wave only CTAF transmissions are clarified to ensure your separation plan remains valid; -

- stop at runway holding points and visually check for traffic prior to runway entry; -

- where possible all aircraft to use the into wind (duty) runway for departure so aircraft are not departing from opposite ends of the runway; and –

- ensure AFRU responses on the CTAF frequency are heard clearly. 

Safety action by Civil Aviation Safety Authority 

On 9 September 2025, CASA advised that new guidance and recommendations relating to the use of radios where the antenna is mounted on the underside of the aircraft fuselage to both Advisory Circular (AC) 91-10 and AC 91-14 had been updated. 

This guidance advised: 

Pilots operating aircraft with similar antenna placements are reminded that ground-based transmissions, when made using a radio with a fuselage underside antenna, are likely to have an increased risk of not being reliably received by other traffic. To enhance situational awareness and collision avoidance, especially at non-controlled aerodromes where radio-alerted see‑and‑avoid is critical, pilots are strongly recommended, wherever practicable, to use radios connected to antennas in unobstructed locations, such as an aircraft upper fuselage, for ground communications

Glossary

Sources and submissions

Sources of information

The sources of information during the investigation included: 

• the instructor of VH-XDK
• the crew of VH-QOD
• QantasLink
• Australian Airline Pilot Academy
• Civil Aviation Safety Authority
• Wagga Wagga Airport
• Aviation Bureau de la sécurité des transports du Canada
• De Havilland Aircraft of Canada.

References

ATSB. (2025). Cockpit Visibility Study. Supporting AO-2023-001 – Midair collision involving Eurocopter EC130 B4, . Canberra: Australian Transport Safety Bureau.

Bailey, L. L., & Thompson , R. C. (2000). The effects of performance feedback on air traffic control team coordination: A simulation study. United States: Department of Tranportation. Federal Aviation Administration. Office of Aviation. Civil Aerospace Medical Institute.

Civil Aviation Safety Authority. (2013, December). PIlot's responsibility for collision avoidance in the vicinity of non-controlled aerodromes using 'see-and-avoid'. Canberra, ACT, Australia.

Civil Aviation Safety Authority. (2014). SMS 3: Safety Risk Management: SMS for Aviation, A Practical Guide. Canberra, ACT, Australia.

Federal Aviation Administration. (2011). Introduction to TCAS II Version 7.1. U.S. Department of Transportation.

Federal Aviation Administration. (2024). AC 91-120. Operational Use of Airborne Collision Avoidance Systems. U.S. Department of Transportation.

Hobbs, A. (2004). Limitations of the see-and-avoid principle. Canberra, Australia: Australian Transport Safety Bureau.

International Telecommunications Union (ITU-R). (2019). Recommendation ITU-R P.526-15: Propagation by diffraction. Geneva: ITU.

Nguyen, T., Lim, C., Nguyen, N., Gorden-Brown, L., & Nahavandi, S. (2019). A review of situation awareness assessment approaches in aviation environments. IEEE Systems Journal, 3590-3603.

Parsons, J. D. (2000). The mobile radio proagation channel (2nd ed.). Wiley.

Rappaport, T. S. (2002). Wireless Communications: Principles and Practice (2nd ed). Cambridge University Press.

Reynolds , R., & Blickensderfer, E. (2009). Crew Resource managment and shared mental models: A proposal. Journal of Aviation/Aerospace Education & Research, 15‑23.

Stanton , N., Salmon, P., Walker, G., Salas, E., & Hancock, P. (2017). State of science: situation awareness in individuals, teams and systems. . Ergonomics, 449-466.

Wickens , C., & McCarley, J. (2008). Applied attention theory. Boca Raton FL : CRC Press.

Wickens, C., Hollands , J., Banbury, S., & Parasuraman , R. (2013). Engineering psychology and human performance. Person Bostan, MA

Submissions

Under section 26 of the Transport Safety Investigation Act 2003, the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. That section allows a person receiving a draft report to make submissions to the ATSB about the draft report. 

A draft of this report was provided to the following directly involved parties:

• the Civil Aviation Safety Authority
• the Australian Airline Pilot Academy
• QantasLink
• Wagga Wagga Airport
• Aviation Bureau de la sécurité des transports du Canada
• De Havilland Aircraft of Canada Limited
• the pilot of PA-28
• the crew of Dash 8.

Submissions were received from:

• the Civil Aviation Safety Authority
• the Australian Airline Pilot Academy
• QantasLink.

The submissions were reviewed and, where considered appropriate, the text of the report was amended accordingly.

Appendices

Appendix A – CTAF recordings

Appendix B – Flight Operations Service Letters

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through:  identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. About ATSB reports ATSB investigation reports are organised with regard to international standards or instruments, as applicable, and with ATSB procedures and guidelines. Reports must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2025 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Commonwealth Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this report is licensed under a Creative Commons Attribution 4.0 International licence. The CC BY 4.0 licence enables you to distribute, remix, adapt, and build upon our material in any medium or format, so long as attribution is given to the Australian Transport Safety Bureau.  Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

Investigation summary

What happened

In the early afternoon of 29 September 2023, a QantasLink De Havilland Aircraft of Canada Limited DHC-8-315 (Dash 8) registered VH-TQZ, being operated on a scheduled air transport flight to Melbourne, Victoria, began to taxi at Mildura, Victoria for runway 09. A short time later, an amateur‑built Lancair Super ES registered VH‑VKP, taxied for runway 36 at Mildura for a private flight to Ballarat. 

Both aircraft gave taxi, entering and backtracking calls on the local common traffic advisory frequency. Neither the pilot of the Lancair, or the crew of the Dash 8, were aware of each other. The crew of the Dash 8 gave a rolling call and had commenced their take‑off on runway 09 as the pilot of the Lancair gave a rolling call on runway 36, this was received by the Dash 8 crew with an immediate response given to the Lancair to hold on the runway. Another aircraft, taxiing behind the Lancair for runway 36, advised them to hold position while the Dash 8 departed.

The Dash 8 crossed the runway 09/36 intersection while the Lancair remained on the threshold of runway 36.

What the ATSB found

The ATSB’s investigation identified that the Dash 8 crew were actively engaged in organising separation with other airborne traffic. During this time, the pilot of the Lancair made a taxi call, and then an entering and backtracking call which partially over‑transmitted the Dash 8 checking on other airborne traffic. The crew of the Dash 8 heard neither of the Lancair pilot’s calls. This led to a situation where the crew of the Dash 8 had an incomplete comprehension of the ground‑based traffic at Mildura, and had no knowledge of the Lancair until during the take‑off. In addition, due to the position and distance of the Dash 8, the pilot of the Lancair had no awareness of the Dash 8 or its radio calls until another aircraft advised that the Dash 8 was rolling on runway 09.

The ATSB investigation found that the Dash 8 aircraft type had reduced ground‑based radio reception and transmission strength with other airfield users located behind the aircraft, which affected radio call readability. This reduced the situational awareness for the Dash 8 crew and other traffic. Further, the Dash 8 ground‑based transmissions on VHF COM 2 (which used an aerial on the aircraft underbelly) had reduced strength and clarity compared to VHF COM 1 (which used an aerial on the roof). This likely led to situations where other aircraft had difficulty in receiving and understanding radio transmissions, and the Dash 8 not receiving other traffic radio transmissions. Due to topography and buildings at Mildura Airport, aircraft are not directly visible to each other on the threshold of runways 09, 27 and 36. This, and the lack of a requirement for mandatory rolling calls, increased the risk of aircraft not being aware of each other immediately prior to take‑off.

The ATSB also identified that the QantasLink radio procedure required Dash 8 crews to use the VHF COM 2 radio to broadcast and receive on local frequencies during operations at all non‑controlled aerodromes. This reduced the ground‑based reception and transmission strength of the Dash 8, and therefore reduced the likelihood of radio calls being received in some circumstances.  

Furthermore, the aircraft manufacturer, De Havilland Aircraft of Canada Limited, did not have guidance to operators on the transmission and reception performance limitations of VHF COM 2 radios for ground‑based communications in Dash 8 aircraft.

What has been done as a result

On 6 December 2024, De Havilland Aircraft of Canada Limited issued 2 flight operations service letters relating to radio communications, with one covering Dash 8 100‑300 series aircraft and the other covering the Dash 8 400 series aircraft. The service letters remind operators that ground‑based VHF communications are affected by line of sight and can be impacted by buildings, terrain or aircraft structures and that use of VHF COM 1 is more effective for ground‑based communications with other aircraft on the ground. 

In support of the De Havilland Aircraft of Canada Limited service letters, the ATSB has issued a safety advisory notice (AO‑2023‑050‑SAN‑01) in conjunction with this report to advise operators of Dash 8 aircraft of the potential for reduced ground‑based communications quality of VHF COM 2 radios. The SAN advises all operators and crew of De Havilland Aircraft of Canada Limited Dash 8 aircraft to consider the use of VHF COM 1 radios for all ground‑based communication while operating at non‑controlled aerodromes.

QantasLink has updated its operations manual to reflect the updated minimum company requirements of a rolling call to be made at all CTAF aerodromes. This is to improve procedural consistency across the pilot group, and to reduce the likelihood of traffic conflict. QantasLink has provided guidance to its pilot group on specifics of potential radio communication degradation on the ground at Mildura Airport between runway 36 and 09 thresholds, including the conduct of rolling calls, and required the clarification of broken, suspicious or ambiguous radio calls from other aircraft prior to departure. QantasLink has also made changes to its operations into Mildura Airport, requiring crews to use VHF COM 1 for ground‑based departure communications, however this does not apply to other non‑controlled aerodromes.

In response to the draft ATSB report, QantasLink provided a bowtie qualitative risk assessment on the proposed adoption of modified CTAF radio panel usage, which focused on additional threats, increased complexities and controls. ATSB acknowledges that the risk assessment identified additional threats. However, QantasLink has not provided an assessment of how these threats may pose a higher risk than the existing aircraft collision risk identified in the safety issue. The ATSB notes that the risk assessment does not address aerodromes other than Mildura that may exhibit similar risk factors, namely, radio shielding, visual obstructions, and/or multiple runways. Furthermore, the risk assessment did not take into account the newly introduced advice from the aircraft manufacturer in 2 flight operations service letters. Notwithstanding, the ATSB has closed the safety issue as partially addressed as the risk has been controlled at Mildura. However, noting that the use of VHF COM 2 at other non‑controlled airports for ground‑based traffic communication currently remains unaddressed, the ATSB expects QantasLink will appropriately apply its safety management system to ensure any similar risk is controlled.

As a result of the potential radio interference at Mildura Airport that was investigated in an ATSB investigation (AO-2023-025) into a similar collision‑risk pairing event about 3 months earlier, Mildura Airport successfully established a permanent notice to airmen for Mildura Airport operations as of 4 April 2024. This included the advice that aircraft are not directly visible to each other on the thresholds of runway 09, 27 and 36 and that mandatory rolling calls are required from all aircraft immediately prior to take‑off due to the increased risk of aircraft not being aware of each other. This permanent notice to airman was subsumed into the En Route Supplement Australia publication for Mildura Airport in the 2406 amendment cycle on 13 June 2024. 

Additionally, QantasLink has updated its operations manual to reflect the updated minimum company requirements of a rolling call to be made at all CTAF aerodromes. This was to improve procedural consistency across the pilot group, and to reduce the likelihood of traffic conflict.

Safety message

Communication and self‑separation in non‑controlled airspace is one of the ATSB’s SafetyWatch priorities. Whenever you fly, into either non‑towered or controlled aerodromes, maintaining a vigilant lookout at all times is important. Situational awareness and alerted see‑and‑avoid is an effective defence against collisions, and good airmanship dictates that all pilots should be looking out and not be solely reliant on the radio for traffic separation. Being aware of other nearby aircraft and their operational intentions is important to prevent collisions. Remember that there may be a variety of aircraft of different sizes, flight rules, and performance levels all operating at the same time, in the same airspace.

Pilots can guard against similar issues to those highlighted by this incident by: 

• making the recommended broadcasts when in the vicinity of a non‑controlled aerodrome
• actively monitoring the CTAF while maintaining a visual lookout for other aircraft and constructively organising separation through direct contact with other aircraft
• clarifying radio call over‑transmissions to ensure that all stations in the vicinity have the best chance of updating their mental model of potentially conflicting traffic
• ensuring transponders, where fitted, are selected to transmit altitude information
• ensuring transmissions are made at non‑controlled aerodromes with the radio/antenna that will provide the optimal ground‑based transmission and reception strength. 

The ATSB SafetyWatch highlights the broad safety concerns that come out of our investigation findings and from the occurrence data reported to us by industry. This investigation report highlights the safety concerns around Reducing the collision risk around non-towered airports.

The occurrence

In the early afternoon of 29 September 2023, a De Havilland Aircraft of Canada Limited DHC-8-315 (Dash 8), registered VH‑TQZ, with 4 crew and 50 passengers on board, being operated by QantasLink on a scheduled air transport flight to Melbourne, Victoria, began to taxi at Mildura Airport for runway 090F[1] (Figure 1, blue line). A short time later, an amateur‑built Lancair Super ES aircraft, registered VH-VKP, taxied for runway 36 at Mildura, for a private flight to Ballarat (Figure 1, orange line). The pilot was accompanied by 2 passengers. 

Figure 1: Overview of airport showing Dash 8 (blue) and Lancair (orange) ground tracks

Aircraft in the overhead images are not the occurrence aircraft. Source: Google Earth, annotated by the ATSB

Radio data collected from Mildura Airport CTAF recordings (Appendix A) are overlaid on a Google Earth image of the airfield (Figure 2). These showed that the crew of the Dash 8 (call sign QLINK81) made a taxi call for runway 09 at Mildura (A), with a further entering and backtracking call 72 seconds later (B). The crew of a second Dash 8 (QLINK 404) called taxiing for runway 09 and held short of runway 09 (C).1F[2] 

Figure 2: Sequence of events while the Dash 8 and Lancair taxied to their respective runways

Source: Google Earth, annotated by the ATSB

The Dash 8 flight crew were backtracking on runway 09 while making a series of calls with the pilot of a Tecnam aircraft, about 11 km north of Mildura and a Cessna joining the circuit overhead the aerodrome. The Dash 8 flight crew spent about 11 minutes communicating with the Cessna to establish deconfliction. It was during this time that the pilot of the Lancair made their taxi call on the CTAF (D). 

The flight crew of the Dash 8 had just begun another call to contact the overhead traffic at the same time as the Lancair pilot transmitted an entering and backtracking call for runway 36 (E). This over-transmission made the first 10 seconds of the Lancair pilot’s call unintelligible.

A Mooney aircraft, departing Mildura for Albury, also gave a call about 70 seconds after the Lancair taxi call, stating that they intended to taxi for runway 36 and that they had copied the Lancair also taxiing for runway 36 (F). According to ATSB interviews with the respective pilots, neither the pilot of the Lancair nor the flight crew of the Dash 8 backtracking on runway 09 were aware of each other at this time. 

Subsequent events are shown in Figure 3. After reaching the end of the runway, at 1348:42, the Dash 8 gave a rolling call on 09 for departure (G). After a short backtrack along runway 36, the Lancair gave a rolling call on runway 36 at 1349:06 (H). The Dash 8 first officer immediately responded with ‘aircraft rolling 36, hold’ (I). The Lancair pilot did not recall hearing any calls from the Dash 8.

Figure 3: Sequence of events after Dash 8 commenced take-off

Source: Google Earth, annotated by the ATSB

Believing that the Dash 8 crew’s call may not have been heard by the Lancair, the Mooney pilot relayed to the Lancair that there was another aircraft rolling on runway 09 (J). The Lancair pilot acknowledged and aborted their take-off at 1349:24 (K) as they had not yet begun to roll, at which point the Lancair was stationary at the end of runway 36, about 730 m from the runway intersection. As the Dash 8 had already passed V₁,2F[3] the flight crew continued the take-off.

Context

Pilot information

Flight crew VH-TQZ (Dash 8)

The captain held an Air Transport Pilot Licence (ATPL) (Aeroplane), a valid class 1 aviation medical certificate and reported a total flying time of about 18,500 hours with about 420 of those being on the Dash 8 and about 60 hours as captain. The captain reported being familiar with Mildura Airport and had operated there regularly in the past and recalled operating into Mildura at least 5 times in 2023, with the last flight being the week before the occurrence. 

The first officer (FO) held an ATPL (Aeroplane), a valid class 1 aviation medical certificate, and reported a total flying time of about 3,100 hours, having flown about 700 of those hours in the Dash 8. The FO was familiar with Mildura Airport having regularly operated there over 50 times and had also operated into Mildura the previous week.

Pilot VH-VKP (Lancair)

The pilot held a Private Pilot Licence (Aeroplane) and reported a total flying time of about 200 hours, with about 93 hours on VH-VKP. They held a valid class 2 aviation medical certificate and were familiar with Mildura Airport, however had only operated there 3 or 4 times previously.

Aircraft information

VH-TQZ

The De Havilland Aircraft of Canada Limited DHC-8-315 is a high-wing, pressurised, commuter aircraft powered by 2 turboprop engines. VH-TQZ was manufactured in Canada in 2000 and was first registered in Australia on 29 November 2000. It was registered with Qantas Airways Limited on 8 February 2011, and operated by Eastern Australia Airlines Pty Limited.

VHF radio antenna position and condition

The Dash 8 had 2 VHF antennas installed on the upper and lower fuselage. 

• Number 1 VHF COM antenna (VHF COM 1) mounted on the roof of the aircraft forward of the wings.
• Number 2 VHF COM antenna (VHF COM 2) mounted on the belly of the aircraft (Figure 4).

Figure 4: Dash 8 antenna position

Source: ATSB

The VHF COM 2 antenna was installed onto VH-TQZ on 1 March 2018 with the last reported C‑check3F[4] conducted on VH-TQZ on 1 August 2023. There was no reported corrosion present under the VHF COM 2 antenna and the only recent defects in the previous 6 months related to the VHF COM 2 screen and frequency knob on the head unit inside the cockpit which were subsequently returned to service.

Traffic collision avoidance system 

A traffic collision avoidance system (TCAS) was fitted to the Dash 8. A TCAS interrogates the transponders of nearby aircraft and uses this information to calculate the relative range and altitude of this traffic. The system provided a visual representation of this information to the flight crew and issued alerts should a traffic conflict be identified. Other aircraft do not receive TCAS alerts if they are not fitted with TCAS.

These alerts include:

• Proximate traffic: an alert issued when another aircraft is within 6 NM range (and 1,200 ft vertically if the traffic is transmitting altitude information).
• Traffic advisory (TA): an alert issued when the detected traffic may result in a conflict.
• Resolution advisory (RA): a manoeuvre, or a manoeuvre restriction, calculated by the TCAS to avoid a collision (the closest point of separation is approximately 25 seconds away or less). This alert is inhibited (inactive) on the ground.

Due to its method of operation, a TCAS cannot detect aircraft that are not equipped with a transponder or one with a transponder that is switched off. Additionally, the system is unable to issue an alert for traffic that is not fitted with an altitude reporting transponder (mode C or S), or in circumstances where the mode C or S transponder on board the conflicting traffic is not transmitting altitude information.

The crew of the Dash 8 reported that the TCAS was used regularly by the operator as an aid to identify potential conflicting traffic in the vicinity of a non-controlled aerodrome prior to take-off. 

QantasLink advised that the use of TCAS was not a formalised procedure for monitoring other aircraft ground movements and that TCAS identification on the ground may be unreliable due to system limitations.

The first officer recalled conducting a check of the TCAS prior to rolling on runway 09 and the TCAS only identified airborne traffic in the vicinity of Mildura Airport.

VH-VKP

VH-VKP was a privately owned amateur‑built aircraft Lancair Super ES, built in New Zealand in 1997. It was first registered in Australia on 26 November 2020 to the pilot. The Lancair is a low wing, fixed undercarriage, piston engine, 4‑seat touring aircraft made from composite materials.

VHF radio antenna position

The primary VHF radio antenna on the Lancair was located underneath the rear of the aircraft empennage and was used to make the required broadcasts on the day of the occurrence. No defects or communication problems, either prior to or after the occurrence at Mildura, were reported by the owner.

Lancair transponder operation

The Lancair was equipped with a mode C transponder and the pilot recalled turning the transponder on (and selecting mode C) before entering the runway at 1347. The pilot believed that the transponder was operating and transmitting positional and altitude information during the take-off. The ATSB was unable to identify any transponder data of the Lancair during its taxi at Mildura.

In September 2024, the Lancair had 2-yearly Civil Aviation Order 100.5 instrument checks conducted and it was found that the transponder was transmitting a weak signal, was considered unserviceable and was replaced. It is unknown if this problem existed with the transponder at the time of the incident at Mildura, however recorded transponder data of the Lancair at the time of the occurrence was unavailable.

Meteorological information

At Mildura Airport around the time of the occurrence, the wind was variable at about 3 kt, with clear conditions and good visibility. Four of the pilots involved remember the wind favouring runway 36 with one stating that the wind at the time of the occurrence was from the north at about 5 kt. 

Mildura Airport 

Mildura Airport was a certified aerodrome. The aerodrome had an elevation of 167 ft above mean sea level and had 2 sealed runways, orientated in an east-west, north-south direction. The main east-west runway was 1,830 m long and the secondary, north-south runway was 1,139 m long. 

The airport was serviced by a number of major aviation carriers and a large international flying school and accommodated aircraft as large as Boeing 737s but regularly operated with lower capacity passenger flights from numerous operators. It also accommodated general and recreational aviation flight training schools, charter operators and private flying. The aerodrome terminal building was upgraded in 1994, with further expansion constructed in 2004 due to increased utilisation and growth. Due to aerodrome expansion in recent years, numerous new buildings had been erected, including the site of an international flight training school and the southern general aviation hangar complex. 

The En Route Supplement Australia (ERSA), promulgated by Airservices Australia, provides information to pilots on the operations specific to each aerodrome. The ERSA entry for Mildura Airport detailed that aircraft may not be visible to one another while on the runway. It also stated that the circuit can be busy due to it being a training airfield with multiple runways in use at any time, in conjunction with frequent high-capacity passenger air transport operations (Figure 5).

Figure 5: Mildura Airport ERSA details

Source: Airservices Australia

Airspace and traffic services 

Mildura Airport was located within non-controlled Class G4F[5] airspace and did not have an air traffic control tower. The non-controlled airspace surrounding Mildura Airport was available for use by aircraft operating under visual flight rules (VFR) and instrument flight rules (IFR). No separation service was provided to aircraft operating in this airspace, with pilots responsible for making themselves aware of nearby aircraft and maintaining mutual self-separation. The primary method of traffic separation at Mildura Airport was by visual reference and relied on pilots using ‘alerted see‑and-avoid’5F[6] practices (see Alerted see-and-avoid). 

Common traffic advisory frequency 

The Mildura Airport CTAF was a designated very high frequency (VHF) radio frequency on which pilots must monitor and make positional broadcasts when operating within a 10 NM radius of the aerodrome. For non-controlled aerodromes, including Mildura, there were a number of recommended VHF radio calls (Table 1) to assist traffic coordination and to enhance the situational awareness of pilots operating within the surrounding airspace. 

Visual line of sight limitations

ATSB inspection of Mildura Airport established that from the threshold of runway 36, the threshold of runway 09 was visually obscured by the terminal buildings (Figure 6). The threshold of runway 36 was similarly not visible from the threshold of runway 09.

Figure 6: View from threshold runway 36

Source: Operator, annotated by the ATSB

The ATSB site inspection also identified a lack of line of sight between the thresholds of runway 09 and 27 (either end of the same physical runway about 1,800 m away) when viewed from the occupant height of a road vehicle. This was due to raised terrain along the runway between the two ends (Figure 7).

Figure 7: View from threshold of runway 27

Dash 8 not clearly visible at other end of runway. Source: ATSB

Operations in the vicinity of non-controlled aerodromes

At and around non-controlled aerodromes, pilots are responsible for making themselves aware of nearby aircraft and maintaining separation. Safe operations at non-controlled aerodromes relies on all pilots maintaining an awareness of their surroundings and other aircraft, flying in compliance with procedures, while being observant, courteous and cooperative.

VHF radio is the primary communication tool to provide ‘alerted see-and-avoid’ commonly across aviation from sport and recreational flying to air transport. VHF radio allows for the communication of information (in this instance traffic information) to the pilot from other aircraft (Civil Aviation Safety Authority, 2013). Other tools to enhance ‘alerted see‑and-avoid’ include ground radar, automatic dependent surveillance broadcast (ADS-B), and traffic collision avoidance system (TCAS).

Civil Aviation Safety Regulation 91.630 made certain radio calls (listed in the Part 91 Manual of Standards) mandatory for aircraft that are fitted with or carry a radio. Chapter 21 of the Part 91 Manual of Standards prescribed one type of mandatory broadcast that applied at all non-controlled aerodromes, namely:

When the pilot in command considers it reasonably necessary to broadcast to avoid the risk of a collision with another aircraft.

To aid in increasing situational awareness at non-controlled aerodromes, recommended broadcasts are published by the Civil Aviation Safety Authority (CASA) for pilots to alert other traffic to their location and intentions before take-off, inbound to land at, or if intending to overfly a non-controlled aerodrome. 

Table 1: Recommended radio calls 

Source: CASA advisory circular 91-10 Operations in the vicinity of non-controlled aerodromes

In addition, individual aerodromes can require additional broadcasts due to unique circumstances by adding a requirement into the ERSA entry for their aerodrome. As seen in Figure 5, the ERSA entry for Mildura did not have any additional broadcast requirements.

CASA advisory circular 91-10, Operations in the vicinity of non-controlled aerodromes, provided further guidance on operations at non-controlled aerodromes, including that:

• In addition to making positional broadcasts, pilots should listen to other broadcasts to increase situational awareness

• Whenever pilots determine that there is a potential for traffic conflict, they should make radio broadcasts as necessary to avoid the risk of a collision or an Airprox event. Pilots should not be hesitant to call and clarify another aircraft’s position and intentions if there is any uncertainty.

Alerted see-and-avoid

Issues associated with unalerted see-and-avoid have been detailed in the ATSB research report Limitations of the See-and-Avoid Principles(Hobbs, 1991). The report highlights that unalerted see-and-avoid relies entirely on the pilot’s ability to sight other aircraft. An ‘unalerted’ search is one where reliance is entirely on the pilot searching for, and sighting, another aircraft without prior knowledge of its presence. 

An ‘alerted’ search is one where the pilot is alerted to another aircraft’s presence, typically through radio communications or aircraft-based alerting systems. Broadcasting on the CTAF to any other traffic in the vicinity of a non-controlled aerodrome is known as radio-alerted see-and-avoid and assists by supporting the pilot’s situational awareness and visual lookout for traffic with the expectation of visually acquiring the subject in a particular direction. The ATSB research report found that an alerted search is likely to be 8 times more effective than an unalerted search, because knowing where to look greatly increases the chances of sighting traffic.

Positional broadcasts

Traditionally VHF radio broadcasts are made at non-controlled aerodromes in order to provide situational awareness, traffic separation and deconfliction to other traffic in the vicinity of the aerodrome.

However, positional broadcasts rely on the accuracy of the information being broadcast and the ability of other traffic receiving, comprehending and reacting to this information.

Civil Aviation Advisory Publication (CAAP) 166-2(1), Pilots’ responsibility for collision avoidance in the vicinity of non‑controlled aerodromes using ‘see and-avoid’ stated:

11.5 Pilots should be mindful that transmission of information by radio does not guarantee receipt and complete understanding of that information. Many of the worst aviation accidents in history have their genesis in misunderstanding of radio calls, over-transmissions, or poor language/phraseology which undermined the value of the information being transmitted.

11.6 Without understanding and confirmation of the transmitted information, the potential for alerted see-and-avoid is reduced to the less safe situation of unalerted see-and-avoid.

Positional broadcasts are a one-way communication, intended to provide a short and concise broadcast to minimise radio channel congestion. However, they do not imply receipt of information by other parties unless direct radio contact is made between stations to acknowledge the traffic, confirm intentions and if required, discuss measures to provide deconfliction. 

The successful broadcast of the information is also subject to limitations of the VHF radio system.

VHF radio line of sight limitations

The VHF radio requires line of sight between both stations in order to function effectively. If an aircraft does not have a clear visual path direct to another in the vicinity, then the radio wave signal strength and clarity can be affected by obstacles. In some cases, terrain, vegetation or buildings can create areas that may shield or substantially reduce radio wave propagation and adversely affect broadcast signal strength and clarity.

At Mildura Airport, VHF radio calls on the CTAF frequency were recorded from an antenna south of the main terminal. Due to its elevated position, this antenna is within line of sight of the entire runway environment. 

The Dash 8 operator’s internal investigation report identified that instrument flight rules (IFR) taxi calls and entering backtracking calls were recorded well, however reduced radio strength and clarity existed with broken radio calls and aircraft unable to hear each other when on the thresholds of runway 09/36. 

Transponder operation at non-controlled aerodromes

Historically, transponders have usually been switched to the standby mode on engine start‑up and taxi. This was done to prevent clutter or false collision avoidance information to airborne traffic while not an immediate collision risk on the ground. If a transponder was fitted, pilots were required to select the transponder to ‘on’ and if mode C or S (that is, altitude information output) was available, this was to be selected to ‘on’ before entering the runway.

The introduction of Civil Aviation Safety Regulation 1998 (CASR) Part 91 basic operating rules commenced on 2 December 2021 and included a change to the required operation of aircraft fitted with a functioning transponder. This change required the selection of the transponder to a transmitting mode prior to the aircraft moving under its own power for the intention of take-off. This is particularly important in a non-controlled aerodrome environment where any form of enhanced situational awareness to all flight crew is paramount to avoiding the risk of collision.

Witnesses’ recollections

Dash 8 crew at the holding point

The crew of the second Dash 8 (QLINK 404) that taxied to holding point Charlie believed that all radio calls appeared normal, and it was their understanding that all parties seemed to know what was going on. They reported being aware of the 2 aircraft taxiing for runway 36. The FO recalled the Lancair taxi call, and the captain recalled the entering or backtracking call and the lining up call from the Lancair. They both recalled the first Dash 8 organising traffic and their rolling call. The crew of the second Dash 8 described the radio signal strength of the Lancair as ‘staticky’ and ‘scratchy’ with a readability score of 2 out of 5.

Mooney pilot taxiing for runway 36

The pilot of the Mooney that taxied behind the Lancair, noted that they heard all the radio calls made by all aircraft and that they did not believe that their reception was blocked by airport shielding. The pilot recalled that they were holding at the taxiway Alpha holding point as the Dash 8 made their rolling call, at about the same time the Lancair had completed their enter and backtrack. Shortly after that, the Lancair called rolling on runway 09, to which the rolling Dash 8 replied to hold position. Worried that the Lancair had not heard this broadcast, the pilot of the Mooney advised the Lancair of the departing traffic.

Dash 8 operator radio procedure

The QantasLink Dash 8 standard operating procedure for departure from a non-controlled aerodrome, at the time of the occurrence, required VHF COM 1 to be set to the area frequency and VHF COM 2 to be set to the CTAF, as passenger boarding commenced. 

Prior to releasing the handbrake to taxi, a call was to be made to the relevant air traffic centre on VHF COM 1 and then followed by a taxi call to the CTAF on VHF COM 2. The departing aircraft was to remain on the CTAF until after departure and clear of the CTAF, only then was the VHF COM 2 selected to 121.5 Mhz.

As a result of a related event on 6 June 2023 (see ATSB investigation report AO-2023-025), the operator provided its crew with a route manual amendment for Mildura on 8 June 2023 with a caution that: 

Crew must be extra vigilant when managing the threat of cross-strip operations at Mildura. Aircraft operating on cross runways may not be visible to each other. When operating from runway 09, the runway 36 threshold and touch down zone will not be visible.

Radio wave degradation is likely to occur on the ground due to terrain and obstacle shielding. This radio shielding is most likely to occur when one aircraft is operating on runway 09 (west of Taxiway D), and other aircraft is positioned on runway 36 (south of taxiway A).

Due to reduced visibility and radio wave degradation threats, flight crew are required to:

• Conduct a rolling call for all departures.

• Clarify any broken, suspicious or ambiguous radio calls from other aircraft prior to departure.

In the course of this investigation, QantasLink issued a technical advisory bulletin, effective from 17 July 2024, which changed the VHF communications procedure for Mildura departures. The aim of the change was to improve ground‑to-ground CTAF VHF communication during the taxi phase. The changed procedure required use of the VHF COM 1 system, noting that this was found to have an improvement in both transmission clarity and reception.

Tests and research – radio signal strength and clarity 

The ATSB conducted VHF signal strength and readability testing, undertaken on 13–14 March 2024 at Mildura Airport. The aim of the testing was to establish if signal strength degradation was occurring due to line of sight limitations and obstacles on the airport or/and if radio signal strength and clarity was aircraft related. 

The testing included numerous stakeholders including expertise provided by Australian Communications and Media Authority (ACMA), Airservices Australia, QantasLink, Mildura Airport management, aerodrome reporting officers (ARO) and a local operator.

ACMA was consulted in the development of the testing schedules and assisted the ATSB during the testing with measuring equipment, by recording radio signal strength data and providing advice. All stakeholders, with the exception of the local operator, were consulted on the testing schedules prior to the conduct of the testing. 

The testing comprised of signal strength, readability and clarity assessments to and from various locations on the aerodrome. The testing focused on the circumstances related to the runway incursion, concentrating on the quality of radio transmissions on the airfield and in particular between the threshold of runways 09 and 36. 

Testing specific to Dash 8 aircraft was conducted on VH-SBI, provided by the operator. This involved reception signal strength testing of aircraft transmissions.

Test schedules

The testing comprised of 4 schedules:

• Schedule 1 involved aerodrome signal reception strength and readability testing. This comprised of measuring the strength and readability of radio transmissions to and from VHF radios in ARO vehicles at relevant points on the airfield (Figure 8).
• Schedule 2 involved light aircraft signal reception strength and readability testing. This was achieved by testing transmissions to and from a light aircraft to an ARO vehicle to measure the strength and readability of radio transmissions of both stations.
• Schedule 3 included Dash 8 signal strength testing. By transmitting from relevant points on the airfield using the testing Dash 8 aircraft’s VHF radios COM 1 and COM 2, and an ARO vehicle to measure the strength and readability of radio transmissions.
• Schedule 4 involved Dash 8 airframe signal strength and shielding testing. This was achieved by recording the test Dash 8 aircraft’s VHF radios COM 1 and COM 2 reception strengths and readability of radio transmissions around the aircraft at about 20 m distance using an 8-point clock code.

Figure 8: Test locations at Mildura Airport

Source: En Route Supplement Australia, annotated by the ATSB

Signal strengths and readability measurements

The signal strength measurement recorded during the testing was the signal power level received from the radio transmission on the ACMA equipment at various locations remote from the aircraft or vehicle. Signal strength was measured in dBm which represents decibels relative to a milliwatt (mW). This is the power ratio in decibels (dB) of the measured power referenced to one milliwatt.6F[7]

A stronger and acceptable signal is one higher than −70 dBm. A weaker, unreliable signal is less than this towards a level of −100 dBm. Stronger signal strength results in more reliable and clear communications. 

ATSB also recorded a radio signal readability test. For this, a qualitative 1–5 readability scale provided by ACMA (Table 2) was recorded at the receiving locations. To avoid subjectivity, these scores were recorded by ATSB, ACMA and Airservices employees and averaged to arrive at an agreed value to accurately represent the call readability.

Table 2: VHF radio readability scale

Aerodrome signal strength, shielding and readability testing

Schedule 1 testing was conducted on the afternoon of 13 March 2024 at about the same time of day as the occurrence. It measured the signal strength and readability during CTAF transmissions from ARO car 2 (ARO and ATSB investigator) transmitting from locations at Mildura Airport (Figure 8). Signal strength measurements and readability assessments were recorded by the ATSB and ACMA staff using ACMA measuring equipment in ARO car 3 which relocated around the aerodrome for the series of tests. Observers of the testing, including Airservices and a Mildura ARO were also in ARO car 3. 

Additional signal strength readings were taken by an ACMA officer from their vehicle, designated ACMA car 1, located near the AVDATA antenna at Mildura Airport (Figure 8). ARO car 2 also conducted a readability assessment of ARO transmissions from ARO car 3 and recorded their readability testing.

The testing identified that between the radio transmission points on the aerodrome, the lesser the distance and greater the line of sight, the clearer the radio transmission was with a readability of 4 (readable with practically no difficulty) or more and signal strengths of greater than −70 dBm.

The testing also identified that the most significant reduction in recorded signal strength and readability was received when transmitting greater distances at:

• the runway 36 threshold to the threshold of runway 09, which reduced readability to 3 (readable but with considerable difficulty) and had a weaker signal strength of less than −70 dBm
• transmitting from the runway 27 threshold to the runway 09, resulting in readability of 3 (readable but with considerable difficulty) and a weaker signal strength of less than −70 dBm
• transmitting from the runway 09 threshold with slight general reduction in signal readability across all other runway thresholds and holding points to 4 (readable with practically no difficulty), but a general reduction in signal strength of less than −70 dBm across all readings.

The results of schedule 1 are shown in Appendix B.

Light aircraft signal strength and readability testing

Schedule 2 testing was conducted on the morning of 14 March 2024. However, due to the unavailability of Lancair VH-VKP due to inclement weather, the Aero Dynamic Flight Academy at Mildura provided Cessna 172, VH-ZJA and an instructor to assist with the testing. 

Signal strength and readability during CTAF transmissions from VH-ZJA (Instructor and ATSB investigator) were conducted, transmitting from locations at Mildura Airport. Signal strength measurements and readability assessments were recorded by the ATSB and ACMA staff using ACMA measuring equipment in ARO car 3 which also relocated around the aerodrome for the series of tests. Observers of the testing, including Airservices and a Mildura ARO were also in ARO car 3. 

The testing identified that between the aircraft radio transmission points on the aerodrome, the lesser the distance and greater the line of sight, the clearer the radio transmission was with a readability of 4 (readable with practically no difficulty) or more and signal strengths of greater than −70 dBm.

The testing also identified that the most significant reduction in recorded signal strength and readability was received when transmitting greater distances at:

• transmitting from the Mildura fuel bowser to the threshold of runway 09, which may be indicative of close proximity hangar shielding
• when receiving from the fuel bowser, a general reduction in signal strength to taxiway Charlie, Delta and the runway 09 threshold greater than −70 dBm.

However, the readability scores in this testing did not score less than 3 (readable with considerable difficulty).

The results of schedule 2 testing are shown in Appendix 2. 

Dash 8 signal strength and readability testing

Schedule 3 testing was conducted on the afternoon of 14 March 2024 at around the same time as the occurrence and measured the signal strength and readability during CTAF transmissions from a QantasLink DHC-8-316, Dash 8 aircraft, VH-SBI. 

The VHF radios installed in both VH-SBI (test aircraft) and VH-TQZ (occurrence aircraft) were Collins Aerospace VHF Transceiver Model: VHF-22C, Part No: 822-1113-021, with RF Power Output 20W Nominal/16W Minimum. These were installed after being released to service in 2022 in Singapore. 

Dash 8 flight crew with an ATSB investigator conducted a modified schedule 1 test using both the No 1 VHF COM antenna (VHF COM 1) mounted on the roof of the aircraft forward of the wings and No 2 VHF COM antenna (VHF COM 2) mounted on the belly of the Dash 8 (Figure 4) to provide comparative ground-based signal strength and readability results. The testing focused on the recorded signal strength and reception of radio signals to and from the Dash 8 to ATSB and ACMA staff using ACMA measuring equipment in ARO car 3 which relocated around the aerodrome for the series of tests.

The purpose of this testing was to ascertain if there were any limitations of the reception and transmission of radio signals that may be affected by attenuation of the signal due to reflection, refraction or shielding from aircraft structure and what limitations this might have on both VHF COM 1 and COM 2.

This testing was conducted by the Dash 8 transmitting on VHF COM 1 first and subsequently from COM 2 from 6 locations around Mildura Airport (Figure 8). These locations were at: 

• gate 3 (nose in)
• hold point taxiway C
• hold point taxiway D
• starter extension on runway 09
• runway 09 threshold
• 1,500 ft into runway 09.

The ARO vehicle (car 3) with the ACMA staff and test equipment then progressed to various locations around the airport to take transmission and readability measurements. The stationary ACMA vehicle (car 1) recorded measurements of the same VH-SBI transmissions.

The testing identified that between the Dash 8 and the radio reception points on the aerodrome, the lesser the distance and greater the line of sight, the clearer the radio transmission was with a readability of 4 (readable with practically no difficulty) or more and signal strengths stronger than −70 dBm.

The testing also identified that the most significant reduction in recorded signal strength and readability was received when transmitting greater distances at:

• receiving and transmitting from the runway 09 starter extension to the runway 36 threshold on VHF COM 2 scored a readability assessment of 2 (readable now and then), and signal strength weaker than the −70 dBm acceptable signal strength limit
• receiving and transmitting from the runway 09 threshold to the runway 36 threshold on VHF COM 2 with a readability of 1 (unreadable), and −85 dBm signal strength, 15 dBm weaker than the acceptable signal strength of −70 dBm
• receiving transmissions from the 09 threshold or starter extension to taxiway Alpha on VHF COM 2 with a readability of 1 (unreadable), and −85 dBm signal strength, 15 dBm weaker than the acceptable signal strength of −70 dBm

It was identified that transmission and reception from the Dash 8 were considered 1 (unreadable) from the runway 09 threshold to the runway 36 threshold on VHF COM 2, while these were 5 (perfectly readable) to 4 (readable with practically no difficulty) on VHF COM 1.

Testing also identified a significant reduction in recorded signal strength and readability was recorded when the Dash 8 was:

• parked at gate 3 (nose in) transmitting and receiving to the threshold of runway 27 on VHF COM 2
• transmitting and receiving from holding points Delta and Charlie to the runway 36 threshold and holding point Alpha on VHF COM 2.

General trends identified from schedule 3 testing were that:

• Dash 8 VHF radio readability was most adversely affected by stations transmitting from directly behind the Dash 8 on both VHF COM 1 and 2 with slightly reduced readability and increasing signal weakness with increasing distance.
• VHF radio readability was adversely affected by increased distance between the ground-based stations, this was more evident on VHF COM 2, leading to unreadable radio signal readability and weaker signal strength.
• VHF readability was somewhat adversely affected from the runway 27 threshold to the runway 09 threshold using VHF COM 2, however Dash 8 reception from the runway 09 threshold reduced further to become only 2 (readable now and then).

Dash 8 airframe signal strength and shielding testing

The purpose of schedule 4 testing was to ascertain if there were any limitations of the reception and transmission of radio signals that may be affected by attenuation of the signal due to reflection, refraction or shielding from aircraft structure and what limitations this might have on both VHF COM 1 and COM 2.

The testing was conducted on the Mildura apron, adjacent to parking bay 3, with VH-SBI facing towards the terminal (nose in), simulating the startup position with engines running. An ATSB investigator was also present on the flight deck with operator’s crew. ATSB and ACMA staff conducted a ground-based signal strength and readability test from the tarmac at about 20 m distance from the aircraft at 8 cardinal points around the aircraft (Figure 9). The testing was restricted to close proximity testing and possible results from a greater distance may vary. However, the magnitude of variation even at close distance was considered significant. 

Figure 9: Dash 8 airframe signal strength and shielding testing

It should be noted that when considering these schematics the higher dBm figures (less negative and located on the outside of the antennae radiation pattern) are of a stronger signal strength level with a greater readability. Source: ACMA test data, annotated by the ATSB 

Testing identified that:

• the signal strength was strongest towards the front of the aircraft and weakest to the rear using VHF COM 1
• the signal strength of VHF COM 2 was consistently less (greater than half strength) at all locations with the VHF COM 2 maximum loss (−10 dBm) at the front and right rear quarter most notable.
• at the direct rear of the aircraft, the lowest VHF COM 1 strength (−32.7 dBm) was recorded and was consistent with similar levels to VHF COM 2
• transmissions on VHF COM 2 on the ground had significantly reduced strength compared to VHF COM 1 and that radio reception and transmission strength to the rear of the aircraft was reduced on both VHF COM1 and VHF COM 2.

The results of schedule 4 testing are shown at Table 3.

Table 3: 8-point testing VH-SBI

Aircraft antenna installation and condition

The operator identified the VHF COM 2 antenna on the test aircraft, VH-SBI, was installed on 23 March 2020. 

The operator’s approved maintenance program included a company derived task to remove the VHF COM antennas at each 7,000 hr ‘C Check’ and to inspect both the fuselage mounting surface, perforated foil gasket and antenna for corrosion and condition. 

No defects were identified relating to the antenna or base plate mount, either prior to the testing or after.

No corrosion or foreign object damage to the antenna or mount was identified and the operator was not aware of any directives or advisory information from the manufacturer regarding elevated risk of corrosion in this location.

Dash 8 aircraft communications

VHF radio certification – ground-based testing 

The Dash 8 manufacturer, De Havilland Aircraft of Canada Limited, advised that initial ground-based VHF radio testing for original certification was conducted during original certification for the Dash 8 on 29 March 1984, in Downsview, Ontario, Canada and that this involved measuring the field strength intensity of the reception of radio signal of VHF COM 2 in ground-to-ground communications of a single aircraft. The manufacturer confirmed that at the time, there was no requirement for certification to consider the aircraft’s transmission field strength intensity. The testing was recorded by an EMC-25 field intensity meter, connected to the aircraft’s VHF COM 2 antenna on the ground with the aircraft conducting a tight turn while receiving radio transmissions from a ground source located at no less than 2,000 ft (610 m). 

At the time of original certification in 1984, De Havilland Aircraft of Canada Limited identified that the Dash 8 aircraft radio installation was a Collins Aerospace Proline II VHF transceiver Model: VHF-22C. The radio had been certified to the required technical standing orders (TSO)-C37b and C38b standards and complied with the US Federal Communications Commission (FCC) Rules and Regulations, Parts 15 and 87 during certification testing. 

Ground-based communication limitations

The ATSB supplied the above test results to De Havilland Aircraft of Canada Limited for review and comment. It identified that Dash 8 aircraft have a relatively uniform antenna polar pattern of reception on both VHF COM 1 and 2 whilst airborne and that in the air, radio range was near horizon limits. De Havilland Aircraft of Canada Limited identified that the original certification testing of the VHF COM 2 was performed at close transmitter/transceiver antenna distances and that the 1984 certification testing indicated a satisfactory result. 

The De Havilland Aircraft of Canada Limited review of the ATSB Mildura test results identified that the signal strength and readability results appeared consistent with the effects of VHF line of site limitations such as physical obstructions, and intervening airport ground and localised aircraft structures, such as fuselage, wings and the tail. 

De Havilland Aircraft of Canada Limited further reported that, due to the physical location of the VHF COM 1 antenna, this would inherently have better line of sight and more reliable performance in ground-based communication with other ground stations when compared to the installation location of the VHF COM 2 antenna 

In response to ATSB questions about what guidance has been provided to Dash 8 operators for the use of the 2 communication channels, De Havilland Aircraft of Canada Limited reported that there was no guidance published by them on best practices for VHF radio communication usage. It was De Havilland Aircraft of Canada Limited’s understanding that this was done at the airline, or national level. 

In terms of the communications issues apparent in this incident, and an earlier incident at Mildura also involving a Dash 8 (see ATSB investigation AO-2023-025), De Havilland Aircraft of Canada Limited reported that it considered the root cause of both events to be operational and not aircraft related. 

De Havilland Aircraft of Canada Limited further identified that due to the lower mounted aerial position of VHF COM 2, that base plate corrosion due to moisture wicking, if not drained correctly, could degrade signal strength. Additionally, antenna damage from foreign objects may also have the same effect.

Related occurrences

Occurrence history

The ATSB reviewed 30 years of recorded occurrences involving Dash 8 aircraft communication difficulties, both in the vicinity of non-controlled aerodromes and during ground-based communications at non-controlled aerodromes from 1995–2024. There were 57 communication occurrences and 51 runway-related occurrences. 

Further review identified that of the above radio communication occurrences between a Dash 8 and another station, there were 25 during approach to land and 27 on the ground where the reason for the radio communication issue remained undetermined. At the time of this occurrence, these undetermined ground-based occurrences were identified across 15 different aerodromes in Australia (see Appendix C). Of these aerodromes, 10 involved a secondary runway and at the time, 4 of which also had dedicated CTAF broadcast procedures due to line of sight limitations during ground-based operations.

Ground‑based air traffic services (ATS) were also identified at 9 of those aerodromes, which provides a local ground‑based radio frequency and one circuit‑based frequency to facilitate communication with air traffic control.

Due to the historic nature of these reported occurrences, it is not possible to provide further analysis of the exact contributing factors of the undetermined events; this could be due to numerous factors not related to limitations to line of sight, Dash 8 VHF COM 2 transmissions or reception. However, all led to a breakdown of alerted see‑and‑avoid during operation within the vicinity of a non-controlled aerodrome.

ATSB investigation (AO-2023-025)

On 6 June 2023, a Piper PA-28-161, registered VH-ENL, taxied for runway 36 at Mildura, Victoria. At about the same time, a QantasLink De Havilland Aircraft of Canada Limited DHC-8-315 (Dash 8), registered VH-TQH, began to taxi for runway 09. Both aircraft broadcast their intentions on the local common traffic advisory frequency. The pilot of the PA-28 was aware of the Dash 8, but the crew of the Dash 8 were not aware of the PA-28. Both aircraft commenced their take-off at about the same time and the Dash 8 crossed ahead of the PA-28 at the runway intersection of 09/36 by about 600 m. 

The pilot of the PA-28 was unable to visually sight the location of the Dash 8 due to airport buildings and assumed that the Dash 8 was still backtracking on runway 09. They did not directly contact the Dash 8 to positively organise separation. They also incorrectly referred to the runway direction at Mildura Airport as ‘runway 35’ instead of ‘runway 36’. 

The Dash 8 crew was focused on obtaining their pre-departure information from air traffic control and had the volume for the radio tuned to the common traffic advisory frequency turned down. An over‑transmission from air traffic control meant that the Dash 8 crew only received certain elements of the PA-28 pilot’s radio calls. This likely led to an incomplete comprehension of traffic by the Dash 8 crew who believed that the PA-28 was not at Mildura (due to the incorrect reference to runway 35). However, they did not seek further information of the source of the radio calls to positively identify the traffic location.

The investigation found that, due to the topography and buildings at Mildura Airport, aircraft are not directly visible to each other on the threshold of runways 09, 27 and 36. The Dash 8 crew did not give a rolling call on runway 09, nor were they required to. The lack of a requirement for mandatory rolling calls increased the risk of aircraft not being aware of each other immediately prior to take-off.

ATSB investigation (AO-2024-009)

On 19 March 2024, a Fairchild SA226-TC Metroliner, registered VH-KGX and operated by CASAIR, taxied at Geraldton, Western Australia for runway 03. About one minute later, a Beechcraft A36 Bonanza, registered VH-CKX and operated by Shine Aviation, taxied for runway 14. After reaching their respective runway thresholds, both pilots attempted to contact the other, however, they did not hear each other, nor could they see each other. A third aircraft assisted by relaying information. Based on the information received, the Bonanza and Metroliner pilots commenced their take-off within 3 seconds of each other. The Metroliner crossed runway 14 about 400 m in front of the Bonanza, with a vertical separation of about 250–300 ft. 

The investigation found that, when aircraft were positioned at the thresholds of runway 03 and 14 (and 08), they will unlikely be visible to each other due to the position of the airport buildings. Further, they may not be contactable on VHF radio due to potential shielding effects. This resulted in the pilots being unable to verify each other’s position and intentions prior to commencing their take-off. 

While the pilot of the third aircraft was attempting to assist, the details provided were inaccurate and incomplete. This inadvertently resulted in misinterpretation by the Bonanza and Metroliner pilots and influenced their decision to take off.

ATSB investigation (AO-2024-041)

The ATSB is investigating a runway incursion involving a De Havilland Aircraft of Canada Limited DHC-8-402 registered VH‑QOD and a Piper PA-28, registered VH-XDK, at Wagga Wagga Airport, New South Wales, on 15 July 2024.

The De Havilland Aircraft of Canada Limited DHC-8 entered active runway 05 as the Piper PA-28 began its take-off roll. The crew of the DHC-8 was made aware of the PA-28 by another aircraft and stopped, reversing the aircraft clear of the runway.

Both crews report making the appropriate radio calls, however, no radio calls were heard from either aircraft reportedly due to known radio shielding.

The investigation is continuing.

Safety analysis

Introduction

On 29 September 2023, a Lancair, registered VH-VKP (Lancair) lined up for take-off on runway 36 at Mildura, however, a QantasLink De Havilland Aircraft of Canada Limited DHC-8-315 registered VH-TQZ (Dash 8), was just becoming airborne on runway 09 at Mildura. The Lancair stopped on the runway after being alerted to the conflicting traffic by the Dash 8 and another aircraft, the Dash 8 crossed ahead of the Lancair at the runway intersection.

This analysis will explore the operational considerations pertaining to radio calls and communication at Mildura Airport, the flight crew and pilot’s mental models, and factors pertaining to the breakdown of communication.

Communication and local traffic mental models

Succinct and timely radio communication is important to ensure high levels of situational awareness and aids in providing enhanced alerted see-and-avoid safety outcomes. As such, the accuracy of the information broadcast by pilots is also critical in ensuring minimum misunderstanding. 

The ATSB investigation considered a range of human factors that could have influenced the decisions and actions of the pilots involved. While both the Dash 8 and the Lancair crews made radio calls in accordance with the applicable regulation and guidance, not being aware of each other meant that they were unable to anticipate the risk of collision and take appropriate action. 

Alerted see-and-avoid relies on crew/pilot awareness of all traffic in the vicinity that may be considered a hazard to their operations. Enhanced situational awareness requires the crew/pilot mental model of the location and intentions of nearby traffic being updated in order to form an evolving understanding of the nearby traffic.

Without this information, the likelihood of effective situational awareness is degraded, and the mental model and shared understanding of hazards is compromised.

During one of the busiest parts of passenger transport operations from a non‑controlled aerodrome, the crew of the Dash 8 were managing the co-ordination and deconfliction of a number of other airborne aircraft in the vicinity of Mildura Airport. This added complexity within the busy phase of pre-departure for the Dash 8 crew and likely led to attentional focus on the identified airborne traffic. Reduced Dash 8 ground-based signal reception associated with distance between the stations, aircraft and geographical shielding, likely reduced the clarity of calls on the CTAF. Although the Lancair pilot’s taxi call was not over-transmitted and was likely received by the Dash 8’s radio, its reduced clarity meant it would have required more of the crew’s attention to notice and interpret.  

A significant amount of radio use was recorded by the Mildura CTAF prior to the occurrence (Appendix A). Substantial use can introduce difficulty in identifying relevant parties, especially during multiple runway operations. The Dash 8 crew had focussed their concern on the identified overhead aircraft as an increased threat to their operation and, while in the protracted process of organising this separation, was not aware of the Lancair. The phenomenon of inattentional blindness, where an unexpected stimulus is not perceived even though it can be physically seen (Mack & Rock, 1998), also applies to auditory stimulus. Known as inattentional deafness, being focused on something else in the auditory environment reduces the chance of hearing an unexpected but salient auditory event (Dehais and others, 2012). The more a person’s attention is required for other tasks, the higher the chance of missing something unexpected, such as the Dash 8 crew missing the Lancair taxi call while focused on overhead aircraft. At an extreme end of this spectrum is cognitive tunnelling where the person is too focused on the task at hand at the expense of what is happening in the present environment (Mack & Rock, 1998).

Such focus can reduce the chance of hearing and therefore appreciating the relevance of other radio broadcasts. The culmination of the Dash 8 crew’s focus likely led to the Dash 8 crew not being aware that the Lancair was taxiing for a conflicting runway.

While the Dash 8 was organising separation with another airborne aircraft, the pilot of the Lancair also broadcast their ‘entering and back tracking’ call at the same time, resulting in an over-transmission and only partial receipt of the Lancair call to the CTAF. The over-transmission was not queried by any of the other local traffic.

This was a missed opportunity that could have allowed the Dash 8 crew to update their mental model as they still had no expectation of another aircraft on the ground that had the potential to become a conflict. The Dash 8 crew continued to focus their attention on airborne traffic. 

Should over-transmission occur, a request for one or both stations to repeat their last transmission is vital to ensuring position and intentions are well known to all other operators in the vicinity. 

The pilot of the Lancair did not hear the calls from the Dash 8, and visual identification of the location of the Dash 8 backtracking on runway 09 was not possible from the threshold of runway 36. This likely reduced the effectiveness of the alerted see-and-avoid principle and prevented the Lancair pilot from seeing the other traffic on runway 09.

Analysis of the radio calls made on the CTAF frequency and the traffic at Mildura, identified that both airborne and taxiing traffic did not witness any direct communication, between either the departing Dash 8 crew or the taxiing Lancair. It is highly likely that both the Dash 8 crew and the Lancair pilot did not either receive or recognise each other’s positional broadcasts and therefore were not able to update their mental model of other aircraft in the vicinity of Mildura Airport at the time. 

The Lancair pilot was aware of other airborne traffic and traffic taxiing behind them as they entered and backtracked runway 36.However, during all the time from start up, taxi and entry to runway 36, they were not aware of the Dash 8 backtracking and holding on the threshold of 09, likely a result of weaker signal strength transmission from the VHF COM 2 of the Dash 8 at the threshold of runway 36, there being no visual line of sight between the thresholds of runway 36 and 09, and localised radio transmission effects between these two locations.

The crew of the Dash 8 were not aware of the presence of the Lancair as a threat to their operation. Although visibility was greater than 10 km with no cloud in the area, start-up, taxi direction and entering the runway orientation of the Dash 8, meant that visibility of the GA apron was limited to the Dash 8 crew with it being behind them. Visual searches prior to take-off on runway 09 for other conflicting traffic were likely obscured by obstacles such as trees, hangars and buildings between the threshold of runway 09 and runway 36.

Furthermore, the Dash 8 crew also checked electronic surveillance equipment prior to departure and did not identify any conflicting traffic. 

In addition to neither crew hearing radio calls from the other aircraft, the above resulted in both crew of the Dash 8 and the pilot of the Lancair having incorrect mental models of the local traffic at Mildura during their take-off. While each of the pilots made assumptions as to local traffic location and intentions, neither were directly aware of each other to positively ascertain traffic separation, resulting in a missed opportunity to utilise the mitigation of alerted see-and-avoid effectively. 

The Mooney pilot taxiing behind the Lancair, became situationally aware of the departing Dash 8 on runway 36 and identified the potential collision risk as the Lancair gave a rolling call on runway 09. At this time, the Dash 8 requested the Lancair stop their take-off, however fearing that the Lancair may not have understood the import of the call, the pilot of the Mooney advised the Lancair to hold their position, due to the departing traffic. This third-party intervention likely prevented a near miss or collision at the runway 09/36 intersection.

Dash 8 radio reception and transmission

The VHF radio strength and readability testing conducted at Mildura on 14 March 2024 by the ATSB in conjunction with the Australian Communications and Media Authority (ACMA), identified that Dash 8 signal strength reception could be adversely affected by the Dash 8’s orientation relative to the other aircraft or antenna locations. Significant recorded signal reduction on both VHF COM 1 and VHF COM 2 radios was observed when the tail of the aircraft was pointed towards the receiver. 

Schedule 3 testing with no geographical or man-made obstructions between stations identified that the Dash 8 with the nose in at the terminal gate and tail pointed to the end of runway 27, recorded a significant drop in readability on VHF COM 2 to the threshold of runway 27 to a readability of 3 (readable with considerable difficulty). Signal strength weakening, over one of the shortest distances tested was also observed. Conversely, testing on VHF COM 2 at the taxiway Charlie holding point to the threshold of runway 27 with almost the same physical distance, but different aircraft orientation at about right angles to the runway 27 threshold, resulted in perfectly readable transmissions and adequate signal strength.

This had the effect of reducing the likelihood that other ground-based airfield users located behind the Dash 8 would either receive the transmission or that the Dash 8 would receive transmissions made by those aft ground-based stations.

This meant that a Dash 8 taxiing from the bay, or at holding points Charlie or Delta, would be orientated with their tail towards the GA parking, refuelling area, taxiway Alpha and the threshold of runway 36. This, coupled with reduced VHF COM 2 strength and readability, significantly reduced the likelihood of transmissions being received and understood by other airfield users, which adversely affected the situational awareness of all operations in the vicinity of the aerodrome.

Testing conducted by ATSB and ACMA measured the transmission power pattern of the VHF COM 2 (via the lower antenna) on the ground and identified that signal reception exhibited significant directional variation, with the average signal strength forward of the aircraft being about 8.5 dB stronger than the average signal strength behind and to the side of the aircraft. Depending on the external physical environment and other factors, this can lead to signal degradation or loss. 

While geographic obstacles and structures between the stations had the likelihood of reducing signal strength and readability in general, it was identified that a significant reduction in radio signal strength and consequent readability existed when VHF COM 2 was used for ground-based communications when compared with VHF COM 1, even when no geographical or man-made structures were present between the stations. It was further identified that Dash 8, VHF COM 2, radio signal strength also declined significantly depending on the distance between ground-based transmission stations. 

VHF COM 2 transmissions made from the starter extension and threshold of runway 09, to a receiver at the threshold of runway 36 or holding point Alpha, lacked the signal strength and readability required for effective communication when compared to the use of VHF COM 1, which had an acceptable level of signal strength and readability despite potential surface-based obstacles that may partially impede VHF radio line of sight. 

Schedule 3 radio signal strength testing from the Dash 8 and readability testing to and from the Dash 8 (Table 4) at taxiway Delta and Charlie with its tail pointing directly towards the holding point at taxiway Alpha and the runway 36 threshold without significant man-made shielding, had reduced Dash 8 VHF COM 2 readability and this was also reflected in the Dash 8 VHF COM 2 readability from taxiway Delta to the threshold of runway 36. 

Table 4: Schedule 3 testing of VHF COM strength and readability

Both these tests with COM 2 indicated recorded strength values 10 to 20 dBm lower than the acceptable level with reduced readability. Comparatively, Dash 8 VHF COM 1 reception at these locations resulted in perfectly readable transmissions with improved signal strength.

Readability at the Dash 8 from taxiway Alpha and the threshold of runway 36 was also found to be significantly reduced on VHF COM 2 with some reduction on VHF COM 1.

Further to this, testing conducted with the Dash 8 at taxiway Charlie, with its tail orientated to the terminal, with a clear line of sight to both taxiway Alpha and the threshold of runway 36, showed reduced Dash 8 VHF COM 2 transmission readability and signal strength readings lower than the acceptable level. Comparatively, the Dash 8 VHF COM 1 reception at this location resulted in perfectly readable transmissions with improved signal strengths. 

The readability at the Dash 8 from taxiway Alpha and the threshold of runway 36 was also found to be reduced significantly on VHF COM 2 with some reduction on VHF COM 1 readability.

The reduction of transmission strength and readability of VHF COM 2 broadcasts, coupled with the reduced transmission reception provided to the flight crew, increased the likelihood of the Dash 8 crew and the other operators in the vicinity of a non-controlled aerodrome having communication difficulties.

Given the decades of operation of this aircraft type and related types without widespread reports of radio problems using VHF COM 2 on the ground, and the difficulty in ascertaining and obtaining the applicable standards, the ATSB did not further evaluate certification aspects of the aircraft VHF radio.

Rolling calls at Mildura Airport

Prior to take-off, rolling calls at all non-controlled aerodromes were not required when there was no identified traffic. This determination was based on the situational awareness of flight crew and may not always be correct at aerodromes where visual identification of other traffic is limited by buildings, terrain or vegetation. At Mildura Airport, it has been established that when 2 aircraft are at the thresholds of runway 09 and 36, they are not visible to each other due to buildings and trees. Similarly, 2 aircraft at either end of runway 09/27 intending to take off toward each other, may not be visible due to central runway elevation.

While the lack of visibility may be recognised by some pilots and prompt them to make a take-off rolling call, a lack of awareness of another aircraft will not prompt the pilot to consider the possibility of another aircraft. As such, a reliance on an extra broadcast through recognition of the lack of visibility will often be ineffective, especially when there is no expectation of another aircraft.

Aerodromes can mandate additional broadcasts where there is a need, such as a rolling call to improve flight crew situational awareness of conflicting traffic when there are visibility limitations. Although Mildura Airport had recognised that aircraft may not be visible to each other on the runway prior to take‑off and had this noted in the En Route Supplement Australia (ERSA), they had not mandated any additional mitigating radio calls. 

The need for further radio calls is exacerbated due to topography and buildings at Mildura Airport, with aircraft not directly visible to each other on the threshold of runways 09, 27 and 36.  

Operator procedures

QantasLink procedures required the use of VHF COM 2 for ground-based communication at non-controlled aerodromes. However, the use of VHF COM 2 for ground-based communications was not required for controlled airspace, where ground-based communications were conducted by VHF COM 1. 

Schedule 3 ground-based signal strength testing on Mildura Airport (Table 4) identified a significant and mostly uniform reduction in the Dash 8 VHF COM 2 radio transmission strength and readability compared to the Dash 8 VHF COM 1 system. It was also found that the use of VHF COM 2 reduced ground-based recorded signal strength and call readability to other aerodrome users in comparison with signal strength and readability results from the Dash 8 VHF COM 1 system. 

It was also identified that radio call reception at the Dash 8 was significantly reduced while using VHF COM 2. This was particularly evident during transmissions made in the vicinity of the threshold of runway 09 to most of the other tested locations on the airport.

Procedurally required use of the Dash 8 VHF COM 2 radio system for ground-based communications at non‑controlled aerodromes reduced the likelihood of other aircraft receiving and interpreting their calls in some circumstances. Furthermore, the reduced transmission reception also increased the likelihood of Dash 8 crews not receiving strong and readable radio calls from other aerodrome users.

The use of VHF COM 1 in preference to VHF COM 2 to broadcast and receive on local frequencies during ground‑based operations at non-controlled aerodromes would increase the VHF transmission strength and readability, increasing the likelihood of other aircraft and vehicles on the ground receiving a strong and clear transmission from the Dash 8 aircraft. 

Radio calls made at runway 09 and 36 thresholds with reduced line of sight and at significant distances, compounded by using VHF COM 2, are less likely to be heard by other aerodrome operators. This likely reduced the situational awareness of the Dash 8 crew and all other traffic at Mildura.

In addition, many regional non-controlled aerodromes into which QantasLink Dash 8 aircraft operate have some, if not all, of the attributes of Mildura Airport. However, regardless of cross runways, non-line of sight communication due to geographical or man-made structures, the reduced transmission strength of the Dash 8 ground-based VHF COM 2 transmissions routinely used at all non-controlled aerodromes added a potential risk to clear communications that may degrade situational awareness for all operators. 

ATSB analysis of 30 years of non-controlled aerodrome occurrences involving Dash 8 aircraft communication, identified 25 unresolved radio communication issues during approach and landing and 27 occurrences of radio communication difficulties in ground‑based communication at 15 different aerodromes in multiple Australian states. Some of these exhibit similar characteristics to the occurrence at Mildura.

Manufacturer advice to operators

De Havilland Aircraft of Canada Limited identified that there is no specific guidance provided on the limitations of ground-based communications on VHF COM 2 to operators. Its understanding was that most operators used VHF COM 1 for ground-based communications and that best practice VHF communication usage was conducted at an airline or national level. However, the ATSB identified that without specific knowledge of the nature or limitations of the ground-based communications provided by the manufacturer, including reduced signal strength and clarity, operators would not be in a position to identify and mitigate the risks.

Findings

From the evidence available, the following findings are made with respect to the aircraft separation issue during take‑off involving a Lancair, VH-VKP, and De Havilland Aircraft of Canada Limited DHC‑8-315, VH-TQZ, at Mildura Airport, Victoria, on 29 September 2023. 

Contributing factors

• The Dash 8 crew were actively engaged in multiple communications with airborne traffic to ensure separation for departure, and were not aware of the Lancair taxiing for runway 36.
• The Lancair pilot's entering and backtracking radio call for runway 36 was partially over‑transmitted. This did not afford an opportunity to alert other aircraft as to their location or intentions.
• Neither the Dash 8 nor the Lancair crews heard each other's previous radio calls prior to the Dash 8 taking off on runway 09, and the Lancair gave a rolling call on runway 36.
• Both the Dash 8 and Lancair crews had no awareness of each other at any stage until after the Dash 8 was taking off, and the Lancair pilot gave a rolling call.
• The reduced Dash 8 radio reception and transmission strength to the rear of the aircraft affected radio call readability to and from other airfield users. This reduced the situational awareness for the Dash 8 crew and other traffic.
• Dash 8 ground-based transmissions on VHF COM 2 had reduced strength and clarity. This likely led to situations where other aircraft had difficulty in receiving and understanding radio transmissions, and Dash 8 aircraft not receiving other traffic radio transmissions.
• Due to topography and buildings at Mildura Airport, aircraft are not directly visible to each other on the threshold of runways 09, 27 and 36. The lack of a requirement for mandatory rolling calls increased the risk of aircraft not being aware of each other immediately prior to take-off. (Safety issue)
• The QantasLink radio procedure required Dash 8 flight crews to use the VHF COM 2 radio to broadcast and receive on local frequencies during operations at non‑controlled aerodromes. This reduced the ground-based radio transmission and reception strength, and therefore reduced the likelihood of other aircraft receiving calls in some circumstances. (Safety issue)
• De Havilland Aircraft of Canada Limited did not publish any guidance to operators of Dash 8 aircraft on the transmission and reception performance limitations of VHF COM 2 radios for ground-based communications. (Safety issue)

Other finding

• Third party intervention by the Mooney pilot prevented the Lancair from rolling on runway 36. The Lancair pilot held on the runway until the Dash 8 departed.

Safety issues and actions

Threshold visibility

Safety issue number: AO-2023-050-SI-01

Safety issue description: Due to topography and buildings at Mildura Airport, aircraft are not directly visible to each other on the threshold of runways 09, 27 and 36. The lack of a requirement for mandatory rolling calls increased the risk of aircraft not being aware of each other immediately prior to take-off.

Operator radio procedure

Safety issue number: AO-2023-050-SI-02

Safety issue description: The QantasLink radio procedure required Dash 8 flight crews to use the VHF COM 2 radio to broadcast and receive on local frequencies during operations at non-controlled aerodromes. This reduced the ground-based radio transmission and reception strength, and therefore reduced the likelihood of other aircraft receiving calls in some circumstances.

Dash 8 operator guidance

Safety issue number: AO-2023-050-SI-03

Safety issue description: De Havilland Aircraft of Canada Limited did not publish any guidance to operators of Dash 8 aircraft on the transmission and reception performance limitations of VHF COM 2 radios for ground-based communications.

Safety advisory notice to operators and crew of De Havilland Aircraft of Canada Limited DHC-8 aircraft

The Australian Transport Safety Bureau advises all operators and crew of De Havilland Aircraft of Canada Limited DHC-8 (Dash 8) aircraft to consider the use of VHF COM 1 radios for ground-based communication while operating at non-controlled aerodromes to improve radio transmission and reception with other stations.

Safety action not associated with an identified safety issue

Safety action by QantasLink addressing CTAF operations

• The introduction of rolling calls at all CTAF aerodromes through introduction of changes to their current operations manual.
• Pilot group provided further guidance on specifics of potential radio wave degradation on the ground between runway 36 and 09 thresholds at Mildura.

Glossary

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the pilot of VH-ENL
• the crew of VH-TQH
• the crew of QLINK 404
• The pilot of VH-NNR
• QantasLink
• De Havilland Aircraft of Canada Limited
• Civil Aviation Safety Authority
• Airservices Australia
• Mildura Airport
• AVDATA
• ADSB data

References

Bell, M., Facci, E., & Nayeem, R. (2005). Cognitive Tunnelling, Aircraft-Pilot Coupling Design Issues and Scenario Interuption Under Stress in Recent Airline Accidents. 2005 Inernational Symposium on Aviation Psychology, (pp. 45-49).

Civil Aviation Safety Authority. (2013, December). PIlot's responsibility for collision avoidance in the vicinity of non-controlled aerodromes using 'see-and-avoid'. Canberra, ACT, Australia.

Civil Aviation Safety Authority. (2021, November). Operations in the vicinity of non-controlled aerodromes. Canberra, ACT, Australia.

Dehais, F., Causse, M., Regis, Régis, N., Menant, E., Labedan, P.,  Tremblay, S. (2012). Missing Critical Auditory Alarms in Aeronautics: Evidence of Inattentional Deafness? Proceedings of the Human Factor and Ergonomics Society Annual Meeting, (p. Vol 56).

Hobbs, A. (1991). Limitations of the see-and-avoid principle. Canberra: Australian Transport Safety Bureau.

Mack, A., & Rock, I. (1998). Inattentional blindness. Cambridge MA: MIT Press.

Submissions

Under section 26 of the Transport Safety Investigation Act 2003, the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. That section allows a person receiving a draft report to make submissions to the ATSB about the draft report. 

A draft of this report was provided to the following directly involved parties:

• Civil Aviation Safety Authority
• Airservices Australia
• Mildura Airport
• QantasLink
• De Havilland Aircraft of Canada Limited
• pilot of VH-VKP
• crew of VH-TQZ
• crew of QLNK 404.

 Submissions were received from:

• Civil Aviation Safety Authority
• QantasLink
• De Havilland Aircraft of Canada Limited.

The submissions were reviewed and, where considered appropriate, the text of the report was amended accordingly.

Appendices

Appendix A – Recorded VHF radio transmissions

Table 5: Recorded VHF radio transmissions

UTC 29 Sept	Origin	Call transcript
1343:14:00	QLINK 81	Mildura traffic QLINK 81, taxi's runway 09 for Melbourne
1344:26:00	QLINK 81	Mildura traffic QLINK 81, enters and backtracks full length runway 09 Mildura
1345:00:00	QLINK404	Midura traffic, QLINK 404, taxies runway 09, will hold short of runway for now, Mildura.
1345:22:00	QLINK*81	Zulu Papa Victor, QLINK 81
1345:32:00	QLINK 81	And 1769, QLINK 81
1345:27:00	Tecnam 1769	QLINK 81, 1769 go ahead
1345:30:00	QLINK 81	We are about to line up and roll on 09, will be making a right turn for departure to Melbourne, can you confirm your current position north of the field?
1345:48:00	Tecnam 1769	Can do, 6 NM to the north of the field at the moment
1345:55:00	QLINK 81	Understood, just need you remain north of the field until we have departed?
1346:00:00	Tecnam 1769	Understood, will remain north of the field until you have departed.
1346:04:00	QLINK 81	Zulu Papa Victor, QLINK 81
1346:23:00	VH-ZPV	Traffic, Zulu Papa Victory passing 2,000 ft, descending to 1,200, going mid-downwind 27, Mildura traffic
1346:44:00	Lancair	Mildura traffic, Lancair Victor Kilo Papa, taxiing for runway 36, Mildura traffic.
1346:51:00	QLINK 81	Zulu Papa Victor, QLINK 81
1346:54:00	ZPV	Zulu Papa Victor, reading correct, going cross wind 09, Mildura traffic
1347:01:00	QLINK 81	Copied, so you’re joining runway 09, is that correct?
1347:06:00	ZPV	Copied that, going crosswind 09, Mildura traffic
1347:25:00	ZPV	Mildura traffic, Zulu Papa Victor, remaining on the dead side, Mildura traffic.
1347:34:00	Mooney	Traffic Mildura CTAF, November November Romeo a Mooney, taxiing for Albury, runway 36 for departure. Copied Lancair, also taxiing runway 36.
1347:47:00	QLINK 81	Zulu Papa Victor just confirm…
1347:51:00	Lancair	(Over‑transmission; QLINK 81 continuing transmission and likely part of Victor Kilo Papa call for entering and backtracking runway 36)
1347:56:00	Lancair	…back tracking runway 36
1347:58:00	ZPV	Zulu Papa Victory, tracking dead side 09, Mildura traffic
1348:24:00	ZPV	Zulu Papa Victory, maintaining dead side 09, Mildura traffic
1348:42:00	QLINK 81	Mildura, QLINK 81, rolling runway 09 for upwind departure.
1349:06:00	Lancair	Mildura traffic, Lancair Victor Kilo Papa rolling runway 36 for straight out departure to the north, Mildura traffic.
1349:14:00	QLINK 81	…aircraft rolling 36, hold.
1349:19:00	Mooney	Victor Kilo Papa hold there, aircraft taking off 09.
1349:24:00	Lancair	Victor Kilo Papa
1349:50:00	Mooney	Good to go now sir
1349:54:00	Lancair	VKP rolling runway 36, departure to the north, VKP, Mildura traffic.
1350:01:00	QLINK 81	Traffic Mildura QLINK 404, Dash 8, entering and backtracking 09 will be for departure to the East, climbing to flight levels.
1350:13:00	Mooney	VKP, your hatch is open sir, on the back of your aircraft
1350:18:00	Lancair	VKP, just caught that
1350:20:00	Mooney	Traffic Mildura, November November Romeo entering and backtracking runway 36 for departure to Albury, copied traffic taxiing runway 09.

Source: Transcribed from Airservices and AVDATA recorded data 29 September 2024

Appendix B – CTAF transmission test results

Schedule 1 test – CTAF transmission testing 

Schedule 2 test – CTAF transmission testing from Cessna 172 VH-ZJA

Schedule 3 test – CTAF transmission testing from Bombardier De Havilland Aircraft of Canada Limited DHC-8-315Q VH-SBI

Appendix C – Aerodromes with historical undetermined Dash 8 communication occurrences

Aerodrome	Number of occurrences	Secondary runway	Line of sight limitations procedures	Details/comments
Armidale, NSW	1	Yes	No	Ground based ATS frequency
Bundaberg, Qld	1	Yes	No	Ground based ATS frequency
Gladstone, Qld	3	No	Yes	Limited to ATS contact on ground due to shielding
Horn Island, Qld	3	Yes	Yes	Due to terrain, Take-off runway 14 and land runway 32 not available Ground based ATS frequency
Mackay, Qld	1	No	No	No details relating to line of sight limitations or ground based ATS frequency
Mildura, Vic	4	Yes	No	Ground based ATS frequency Procedures implemented from April 2024
Moranbah, Qld	1	No	No	No details relating to line of sight limitations or ground based ATS frequency
Moree, NSW	1	Yes	No	Ground based ATS frequency
Port Lincoln, SA	1	Yes	No	Ground based ATS frequency
Port Macquarie, NSW	1	No	No	Ground based ATS frequency
Roma, Qld	2	Yes	No	Ground based ATS frequency
Toowoomba, Qld	1	Yes	Yes	Due to single lane and obstructed visibility, all TFC using TWY and/or taxilane B or C to check for oncoming ACFT and BCST intentions
Wagga Wagga, NSW	3	Yes	Yes	Light ACFT at THR of RWY 23 not visible to other ACFT on the ground using RWY 05. Radio black spots may result under some conditions Further procedures implemented from March 2024 Ground based ATS frequency
Williamtown, NSW	2	No	No	No details relating to line of sight limitations or ground based ATS frequency
Whyalla, SA	2	Yes	No	ATS available in the circuit but not on the ground

Appendix D – Flight Operations Service Letters

 

 

 

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[1]      Runway number: the number represents the magnetic heading of the runway. In this case, ‘09’ represents a magnetic heading of 090 degrees.

[2]      See Witnesses for the recollections of the crew of this Dash 8 and the pilot of the Mooney, discussed below.

[3]       V_1: the critical engine failure speed or decision speed required for take off. Engine failure below V₁ should result in a rejected take off; above this speed the take-off should be continued. 

[4]      A detailed operator maintenance check of the aircraft and systems, which occurs about every 18 months to 2 years (depending on type of aircraft) and takes up to 3 weeks.

[5]      This airspace is uncontrolled. Both IFR and VFR aircraft are permitted and neither require air traffic control clearance.

[6]      Improved visual acquisition by pilots alerted to traffic presence (by radio, electronic conspicuity, or other means). 

^[7]      1 mW = 0 dBm. The dBm scale is logarithmic (so a loss of −3 dBm is half of the signal strength (10^-0.3) and −10 dBm is 10 times less than 0 dBm at 0.1 mW, similarly 0.01 mW = −20 dBm. The closer the value was to 0, the stronger the signal. e.g. −56 dBm is a better signal strength than −90 dBm.

[8]      Bowtie analysis is a risk analysis methodology that uses a visual representation of threats, hazards, consequences, and risk controls.

[9]      When on the ground, pilots often need to communicate with air traffic services that are not located at the airport.