A DeHavilland Dash 8 was conducting an instrument flight rules (IFR) Air Transport flight from Sydney to Narrabri and tracked via Richmond direct to Narrabri at flight level (FL) 180. The flight was conducted in controlled airspace until approximately 130 NM north-north-west of Sydney. The remainder of the flight was then conducted in Class G non-controlled airspace. The crew of the Dash 8 contacted Sydney Flight Service (FS3) at 0721 Eastern Summer Time (ESuT) and reported that the aircraft was maintaining FL180 with an estimate for Narrabri of 0745. (All times are ESuT unless otherwise stated.)
At 0732 the pilot of a Piper Chieftain conducting a visual flight rules (VFR) flight from Wee Waa to Tamworth made an all-stations broadcast on the FS3 frequency. The pilot reported departing from Wee Waa at 0730, tracking 113 (degrees M) and climbing to 7,500 ft. The pilot addressed the report to FS3 and to any other traffic in the Wee Waa area. There was no acknowledgement or response to this report by other aircraft or ground stations. The pilot was rated and licensed for IFR flight but elected to operate VFR for this flight and therefore FS3 was not required to take any action in response to his broadcast.
Approximately 4 minutes after the Chieftain pilot's departure report, the crew of the Dash 8 requested traffic information from FS3 for their descent into Narrabri. FS3 advised that there was no known IFR traffic. The crew acknowledged this advice and reported that the Dash 8 had left FL180, but they did not include their position relative to Narrabri in the transmission.
The track of the Chieftain crossed the track of the Dash 8 approximately 12 NM south-southeast of Narrabri.
As the Dash 8 was passing 8,000 ft, the crew saw a reflection to the left of the nose of their aircraft. Subsequently, they saw a twin-engine aircraft and manoeuvred their aircraft to avoid it. The twin-engine aircraft passed from left to right approximately 300 m in front of them and at about the same level.
The crew of the Dash 8 queried FS3 regarding the other aircraft but were advised that there was no IFR traffic. The crew of the Dash 8 then made an all-stations area broadcast in an attempt to establish communications with the other pilot. The pilot of the Chieftain acknowledged the call and advised the crew that he was tracking from Wee Waa to Tamworth at 7,500 ft and that his aircraft was a Chieftain.
Further discussion established that the pilot had neither seen the Dash 8 nor heard the crew reporting on descent. The crew of the Dash 8 did not remember hearing the departure report from the pilot of the Chieftain.
In non-controlled airspace, flight service are required to provide information to all IFR-category aircraft on other IFR flights to assist crews in determining any conflict situations. However, the flight service information system does not cover VFR traffic. Therefore, in this instance FS3 was not required to provide information on VFR flights to the crew of the Dash 8.
Aircrew are responsible for maintaining their own separation in non-controlled airspace. IFR pilots use known position reports of other aircraft to gain an appreciation of the disposition of traffic and whether there is a need to arrange separation. Pilots of VFR flights are only required to make a limited number of position reports and generally rely on the unalerted "see and avoid" principle to maintain separation from other aircraft; that is, they maintain a continuous lookout for other aircraft.
Radio frequency monitoring
The Chieftain was fitted with two very high frequency (VHF) radios. The pilot selected one to the common traffic advisory frequency (CTAF) and one to the FS3 area frequency while in the Wee Waa CTAF area. After leaving that CTAF area, he changed from the CTAF to the Tamworth automatic terminal information service (ATIS) frequency on one radio while continuing to monitor FS3 on the second radio.
The investigation estimated from aircraft performance data that the Chieftain would have reached the planned level of 7,500 ft just prior to the Dash 8 crew requesting traffic information from flight service. The Chieftain pilot reported that at about that time he was probably listening to the Tamworth ATIS in preparation for requesting a clearance to enter controlled airspace from air traffic control.
The Dash 8 was also fitted with two VHF radios. While operating in controlled airspace, the crew selected the air traffic control frequency on one radio while the other was selected to the aviation emergency frequency. Prior to leaving controlled airspace, the crew selected the FS3 area frequency while continuing to monitor the emergency frequency on the second radio.
The Wee Waa departure report from the pilot of the Chieftain was recorded on the flight service automatic voice recording (AVR) system and was clear and understandable. This departure report was additional to the mandatory reports for VFR flights detailed in the Aeronautical Information Publication (AIP) RAC 64.
AIP RAC 42 paragraph 32.2 required the crew of an IFR aircraft to report their aircraft's position to flight service prior to changing levels. Company operating procedures for the Dash 8 required the crew to make a position report prior to descent when operating in non-controlled airspace. The AVR did not record a position report from the crew of the Dash 8 prior to their commencement of the descent.
The visibility was reported as hazy but in excess of 10 km. The sun was low in the sky and the pilot of the Chieftain had lowered the sun-visor in the aircraft cabin to shield his eyes.
The reason why the crew of the Dash 8 did not hear the Wee Waa departure report by the pilot of the Chieftain, or if they did, why they did not appreciate that there was the potential for conflict, was not determined.
The crew of the Dash 8 had previously reported their position and estimate for Narrabri on first contact with flight service. The reason the crew subsequently did not comply with AIP and company operating procedures, regarding a position report prior to descent, was also not determined.
The monitoring of the Tamworth ATIS transmission by the pilot of the Chieftain may have prevented him from hearing the Dash 8 crew report on descent. Consequently, he was unalerted to the Dash 8. If he had heard the transmission he may have initiated communication to ascertain if there was the potential for conflict. Under the current VFR procedures there was no third party, such as flight service, to alert the pilot to the position of conflicting traffic.
The Chieftain pilot reported that he was using the visor in the cabin but that he did not believe that his view from the aircraft was impaired. However, the fact that he was using the visor would indicate that the rising sun was of some concern and this aspect, in conjunction with the hazy conditions, probably limited his ability to sight potentially conflicting aircraft in his forward field of vision.
Unalerted "see-and-avoid" principle
Despite the Chieftain pilot's departure report, which was additional to that required for VFR flights, the crew of the Dash 8 remained unalerted to the pending conflict. This may have been due to the difficulty of assessing the potential conflict of other traffic from the limited details included in departure reports. In the dynamic aircraft operational environment, even with multiple flightcrew, it is not an easy task to develop a situational awareness of all potential conflicting aircraft.
The provision of a position report by the crew of the Dash 8 prior to commencing descent would have been the main opportunity for the pilot of the Chieftain to be alerted to the potential conflict. However, the report did not contain a reference to the position of the Dash 8 and the Chieftain pilot was unaware of the location of the Dash 8. Additionally, it was possible that the pilot of the Chieftain may not have heard or appreciated the significance of the Dash 8 pre-descent position report even if it had been provided, as he was probably monitoring the Tamworth ATIS at the time. Consequently, in either situation, separation was solely reliant on the pilots' ability to sight other aircraft and to manoeuvre their aircraft in sufficient time to avoid a conflict.
The limited radio reports required from pilots operating VFR flights place an over-reliance on the unalerted "see-and-avoid" principle to maintain separation from other aircraft. This aspect was one of the conclusions in the Bureau's research report titled "Limitations of the See-and-Avoid Principle" (1991) which stated, "Unalerted see-and-avoid has a limited place as a last resort means of traffic separation at low closing speeds but is not sufficiently reliable to warrant a greater role in the air traffic system. BASI considers that see-and-avoid is completely unsuitable as a primary traffic separation method for scheduled services". In that research report BASI recommended that "the CAA should take into account the limitations of see-and-aviod when planning and managing airspace and should ensure that unalerted see-and-avoid is never the sole means of separation for aircraft providing scheduled services".
- The crew of the Dash 8 did not hear the departure report by the pilot of the Chieftain or if they did, they did not appreciate that there was a potential for conflict.
- The crew of the Dash 8 did not include their position when they requested traffic information from flight service prior to leaving FL180.
- The pilot of the Chieftain did not hear the descent report from the Dash 8 crew.
- The track of the Chieftain in relation to the early morning sun limited the pilot's ability to scan for other traffic.
- A reflection off the Chieftain alerted the Dash 8 crew to the presence of the aircraft.
The Bureau of Air Safety Investigation is investigating a number of safety deficiencies relating to aircraft operations in non-controlled airspace with a view to reducing the reliance on the unalerted "see-and-avoid" principle as the primary means of separation for fare-paying passenger flights.
For example, the Bureau issued Interim Recommendation (IR) 970155 to the Civil Aviation Safety Authority on 30 January 1998, which resulted from the analysis of a similar occurrence.
The interim recommendation stated in part:
"The greater use of larger and faster aircraft for RPT flights in non-controlled airspace increases the need for the adoption and use of "separation assurance" techniques in conjunction with "alerted see-and-avoid" procedures by all flight crews.
"Although the inclusion of "separation assurance" techniques in airline flight operations manuals would address the deficiency to some extent, procedures for other IFR and the majority of visual flight rules (VFR) flights are also essential. Many pilots may require guidance and training on "separation assurance" techniques.
"Alerted see-and-avoid" procedures used in conjunction with "separation assurance" techniques provide a fail-safe method of self-separation which enhances safety.
"The Bureau of Air Safety Investigation recommends that the Civil Aviation Safety Authority in conjunction with Airservices Australia:
"Review aviation regulations and instructions, with the aim of maximising the use of "separation assurance" procedures in conjunction with "alerted see-and-avoid" procedures by pilots of flights in Class G airspace.
'The Bureau of Air Safety Investigation further recommends that the Civil Aviation Safety Authority:
"Implement an education program for pilots to promote the use of "separation assurance" procedures in Class G airspace".
The first part of the recommendation was sent to Airservices Australia as IR970175.
|Date:||24 November 1997||Investigation status:||Completed|
|Time:||0743 hours ESuT|
|Location:||25 km SSE Narrabri, Aero.|
|State:||New South Wales||Occurrence type:||Near collision|
|Release date:||01 November 1998||Occurrence category:||Incident|
|Report status:||Final||Highest injury level:||None|
Aircraft 1 details
|Aircraft manufacturer||de Havilland Canada|
|Type of operation||Air Transport Low Capacity|
|Damage to aircraft||Nil|
|Departure point||Sydney, NSW|
|Departure time||0642 hours ESuT|
Aircraft 2 details
|Aircraft manufacturer||Piper Aircraft Corp|
|Type of operation||Private|
|Damage to aircraft||Nil|
|Departure point||Wee Waa, NSW|
|Departure time||0730 hours ESuT|