The operator’s 737 manual provided information on the handling techniques to maintain tail clearance margins during take-off, including take-off in gusty and crosswind conditions.

While the pilot in command (PIC) needed to react quickly and precisely to manage roll in the gusty crosswind conditions, a more measured input of pitch control was required during the aircraft’s rotation to maintain the allowable tail clearance margin. The almost doubling of the average pitch rate of rotation during the take-off indicates that the PIC exceeded the recommended rate. It is possible that the PIC used a similar style of control input for pitch that he was using to manage roll.

This occurrence highlights the fact that during a take-off manoeuvre, tail clearance margins can reduce to the point where a tail strike will probably occur if the recommended rotation rate is exceeded.

On 1 February 2005, a Boeing Company 737-838 (737) was being operated on a scheduled passenger service from Sydney, NSW, to Darwin, NT with two pilots, five cabin crew and 151 passengers. The pilot in command (PIC) was the pilot flying for the take-off. At 1931 Eastern Daylight-saving Time, during lift-off from runway 34 Left (34L), in gusty crosswind conditions, the PIC and co-pilot felt the aircraft's tail strike the runway. They queried the rear cabin crew, who confirmed that there was an unusual noise during the aircraft's rotation. The pilots performed the 737 Quick Reference Handbook (QRH) Non-Normal Checklist for tail strike on take-off. Following completion of the checklist, the PIC elected to return to Sydney for an overweight landing.

An engineering inspection confirmed that the aircraft had sustained a tail strike during the takeoff. A crushable cartridge, fitted to minimise damage to the aircraft during a tail strike, was damaged and required replacement. There was also minor wear to the tailskid shoe. A structural inspection of the tail section and an overweight landing check were completed and the aircraft was found to be serviceable.

The Sydney Airport automatic terminal information service (ATIS) provided meteorological and operational information for pilots of arriving and departing aircraft by means of a continuous and repetitive radio broadcast. The information broadcast at the time advised that runway 07 was in use, the wind direction was 030 degrees M at a speed of 20 kts and gusting to 30 kts. The maximum crosswind was 18 kts [for aircraft operating on runway 07]. Those conditions would have resulted in a crosswind of 16 kts to 23 kts for runway 34L.

The Bureau of Meteorology provided a report of the weather conditions at 1930 as recorded by the automatic weather station at Sydney Airport. The report indicated that there was a north-easterly wind (from 050 degrees T), with a speed of 25 kts and gusting to 35 kts. That resulted in a right crosswind of 22 kts (mean) and up to 31 kts during a gust, for aircraft operating on runway 34L.

The aircraft's weight and balance sheet provided to the pilots by the operator showed that the planned take-off weight was 75,689 kg¹. That resulted in a calculated take-off decision speed (V1) of 150 kts indicated airspeed² (IAS), a rotation speed (Vr) of 151 kts IAS and a take-off safety speed (V2) of 156 kts IAS. The PIC reported that after assessing the performance requirements for take-off, he elected to use runway 34L. The operator's crosswind limit for runway 34L was 33 kts.

The aircraft was fitted with an L3 Communications digital flight data recorder (DFDR). The ATSB analysed the recorded DFDR data to assist in establishing the sequence of events during the occurrence. During the take-off roll, control wheel (right) and rudder (left) inputs were made consistent with a right crosswind. The analysis showed that during the take-off roll the PIC used quick and precise roll control inputs in the gusty crosswind conditions. Fluctuations in the aircraft's calibrated airspeed (CAS) showed that variable wind conditions were experienced during the take-off roll, consistent with the ATIS values. The aircraft was rotated at the calculated Vr of 151 kts IAS. At lift-off, the aircraft's pitch attitude was +10.9 degrees³. By comparison, the average pitch attitude for the 23 previous takeoffs was +5.5 degrees. The average pitch rate of rotation was 3.7 degrees per second, compared with an average pitch rate of rotation of 2.2 degrees per second for the 23 previous flights. The data revealed that immediately prior to rotation, the aircraft was tracking on the runway centreline and the wings were level.

The operator's 737 Flight Crew Training Manual section 3.9 stated that, 'a 2 to 3 degree per second rotation rate is required to achieve a tail clearance of 51 cm'. Section 3.14 states that under gusty wind and strong crosswind conditions, 'do not rotate early or use a higher than normal rotation rate in an attempt to clear the ground and reduce the gust effect because this reduces the tail clearance margins'.

1. Actual brakes release weight at the start of the take-off run.
2. Indicated airspeed is the reading of the airspeed indicator instrument.
3. The pitch attitude mentioned is consistent, allowing for resolution limits, with the Boeing Flight Crew Training Manual (FCTM) tail strike pitch attitude (11.0 degrees).

On 1 February 2005, a Boeing Company 737-838 (737) was being operated on a scheduled passenger service from Sydney, NSW, to Darwin, NT with two pilots, five cabin crew and 151 passengers. The pilot in command (PIC) was the pilot flying for the take-off. At 1931 Eastern Daylight-saving Time, during lift-off from runway 34 Left (34L), in gusty crosswind conditions, the PIC and copilot felt the aircraft’s tail strike the runway. They queried the rear cabin crew, who confirmed that there was an unusual noise during the aircraft’s rotation. The pilots performed the 737 Quick Reference Handbook (QRH) Non-Normal Checklist for tail strike on take-off. Following completion of the checklist, the PIC elected to return to Sydney for an overweight landing. An engineering inspection confirmed that the aircraft had sustained a tail strike during the take-off. A crushable cartridge, fitted to minimise damage to the aircraft during a tail strike, was damaged and required replacement.

The investigation found that while the PIC needed to react quickly and precisely to manage roll in the gusty crosswind conditions, a more measured input of pitch control was required during the aircraft’s rotation to maintain the allowable tail clearance margin. This occurrence highlights that during a take-off manoeuvre, tail clearance margins can reduce to the point where a tail strike will probably occur if the recommended rotation rate is exceeded.

On the 25 January 2006, the operator advised the Australian Transport Safety Bureau they had developed a New Technologies training segment effective 18 January 2006. That training includes the use of the Heading Guidance System (HGS) on the Boeing 737 which will enhance situational awareness during takeoff and landing.

On 25 January 2005, a Boeing 727-51C aircraft, registered in Sierra Leone as 9L-LEK, was being operated on a non-scheduled positioning flight from Cairns to Brisbane, Queensland.

CONCLUSIONS

Significant factors

1. The approach controller did not assign an altitude to the second formation that provided a vertical separation standard between the second formation and the Dash 8.
2. The tower supervisor advised the tower controller to cancel the instruction to the Dash 8 pilots to orbit on the downwind leg of the circuit at 2,500 ft, and to continue on the downwind leg of the circuit.
3. The tower controller was not aware that the second formation was inbound to the circuit.
4. The tower controller did not notify the approach controller that the Dash 8 was extending towards the lateral boundary of the ATZ.
5. The pilots of the Westwind did not join the circuit via the upwind leg as instructed by the tower controller.

Contributing factors

1. The code/flight plan association on the ADATS data block of the second formation terminated.
2. The approach controller removed the second formation's flight progress strip from the flight progress board.
3. The approach controller did not provide the tower controller with voice coordination on the second formation once the code/flight plan association terminated.
4. The pilots of the Westwind incorrectly notified the tower controller that their aircraft was 'minimum fuel' when the aircraft was on left base.
5. The tower controller and the tower supervisor were relatively inexperienced, and each had responsibility for a controller-under-training.

ANALYSIS

Introduction

The tower controller and the approach controller were unable to continue to apply a separation standard between the second formation of Hornets and the Dash 8. This analysis examines the development of the occurrence and highlights the safety issues that became evident as a result of the investigation.

Air traffic control separation standards and procedures

The approach controller's assignment of 3,000 ft to the pilots of second formation of Hornets when they had about 32 NM to fly to land, did not provide either a vertical separation standard or separation assurance between the second formation and the Dash 8. That action precipitated the sequence of events that followed. While a radar separation standard existed initially between the Dash 8 and the second formation, it relied on continuous monitoring by the approach controller. The allocation, by the approach controller, of an altitude to the second formation that would have provided the 1,000 ft vertical separation standard with the Dash 8 would have assured that a separation standard continued to exist. It would also have given the tower controller the option to assign further descent to the pilots of the second formation once a visual separation standard between the second formation and other aircraft joining the circuit could be applied.

The approach controller was required to establish a separation standard between the second formation and the Dash 8, and to have that standard in place before transferring the responsibility for separation to the tower controller. In not providing separation assurance between the second formation and the Dash 8, the approach controller did not demonstrate 'the proactive application of separation standards to avoid rather than resolve conflicts' as stated in the Manual of Air Traffic Services (MATS).

It was likely that the limited data block format displayed on the second formation adversely affected the situational awareness of both the tower controller and the tower supervisor at the time the tower controller advised the pilots of the Dash 8 that they could turn base 'when ready'. The tower controller did not provide traffic information about the location of the second formation to the pilots of the Dash 8 until after the pilots of the Dash 8 advised that they were on a traffic alert and collision avoidance system descent. At the time the tower controller instructed the pilots of the Dash 8 to turn base the second time, the relative locations of the second formation and the Dash 8 placed the aircraft in potential conflict. That would have been apparent to both the tower controller and the tower supervisor had either of them been aware of the location and intentions of the second formation at that time.

The traffic situation in the circuit area became quite complex in a very short period of time. The relative inexperience of the tower controllers may have limited their ability to realise the potential for a relatively simple inbound sequence to develop into an infringement of separation standards.

Communication between the tower controller and the tower supervisor may have been difficult due to the complexity of communication between trainees and their training officers, and between controllers in the various control positions in the tower. Had the Dash 8 remained at 2,500 ft conducting orbits in the downwind position as initially instructed until the tower controller could fit that aircraft into the landing sequence, there may have been more time for the tower controller to:

• liaise with the tower supervisor
• regulate the flow of traffic
• identify the second formation on the situation data display (SDD)
• assess options that may have ensured that separation continued to exist
• evaluate the impact of the late declaration of 'minimum fuel' by the pilots of the Westwind
• provide traffic information where appropriate
• issue alternative instructions.

Once the tower controller notified the approach controller that the Dash 8 had been assigned a visual approach, the approach controller removed the flight progress strip from the flight progress board. After that, there was nothing to prompt the approach controller to critically re-evaluate the information on which the original evaluation, that the aircraft would not come into close proximity, was made, even though there remained a possible confliction between the inbound second formation and the Dash 8.

Although the decision by the tower supervisor to instruct the pilots of the Dash 8 to continue on the downwind leg of the circuit and not conduct the left orbit in the downwind position may have been appropriate, it unnecessarily increased the complexity of the traffic scenario, especially given the training workload in the tower at that time. It also reduced the options available to the tower controller once the Westwind joined the circuit on the left base leg rather than via the initial point, or the upwind leg of the circuit as instructed. The instruction issued to the pilots of the Westwind by the tower controller to enter the circuit via the upwind leg would have provided the Westwind with adequate priority and would not have compromised the safety of the flight. That may also have created an opportunity for the tower controller to locate the second formation on the SDD and therefore reduce the likelihood of an infringement of separation standards.

Tower supervisors have the authority to become involved with tactical air traffic control decisions and may assume control responsibility for sequencing or separation, without formally taking over from the tower controller. Tower supervisors must consider how an instruction to the tower controller might affect the situational awareness of that controller. A supervisor must be prepared to take control of the situation, in which they have intervened at a tactical level, until the tower controller can resume responsibility for separation. Otherwise tower controllers may inherit a scenario from the tower supervisor that they may not entirely understand, with little time to react.

Although the extended downwind of the Dash 8 resulted from the Westwind not complying with a control instruction, the tower controller was required to notify the approach controller that the aircraft was extending and may track beyond the lateral boundary of the Aerodrome Traffic Zone (ATZ). The tower controller did not notify the approach controller that the Dash 8 was extending downwind. Therefore, the approach controller was unaware that the Dash 8 was tracking towards the right initial point, in potential conflict with the second formation.

Minimum Fuel

Military air traffic controllers are familiar with pilots declaring 'minimum fuel' and with their responses in such circumstances. However, the disposition of the Westwind relative to base and final, the relatively complex nature of the traffic pattern at the time of the broadcast, and the training environment that existed in the control tower at the time of the occurrence, all reduced the time available for the controller to consider the impact of the 'minimum fuel' broadcast on the traffic pattern.

By the time the tower controller had an opportunity to assess the impact that that transmission may have on the landing sequence, and to determine what priority could have been provided to the pilots of the Westwind, the Westwind was already on the final approach leg. The pilots of the Westwind did not comply with the instruction by the tower controller to join the circuit on the upwind leg, even though that would have been acceptable in such circumstances. The declaration of 'minimum fuel' in such close proximity to the landing threshold may have distracted the controllers in the tower and reduced the effectiveness of their scans of the tower environment, including the SDD, and added to the complexity of the situation.

Australian Defence Air Traffic System (ADATS)

The approach controller did not provide the tower controller with information on the second formation after the code/flight plan association for that formation terminated. Although the approach controller reported that the termination occurred close to the boundary of tower airspace, the tower controller appeared to be unaware of the proximity of the second formation. Had the approach controller provided the tower controller with coordination on the second formation, in accordance with local procedures, the tower controller's attention would have been drawn to the location of that formation on the SDD. That may have given the tower controller an opportunity to ensure that the Dash 8 remained clear of the inbound path of the second formation.

Sequence of Event¹

On 31 January 2005, a de-Havilland Canada Dash 8-202 (Dash 8) aircraft that was inbound to Williamtown Airport, NSW, on a scheduled passenger service from Brisbane, Queensland, passed within 1 NM laterally and 300 ft vertically of the second of two formations of two McDonnell Douglas Corporation F/A-18 (Hornet) aircraft that were inbound to Williamtown Airport after a training exercise. As the Dash 8 turned onto the base leg, the second formation was about 6 NM north-west of Williamtown Airport, at 2,900 ft above mean sea level. The pilots of the Dash 8 descended in response to a traffic alert and collision avoidance system (TCAS) resolution advisory (RA) they received on that formation. The approach controller did not provide the required separation standard of 1,000 ft vertically or 3 NM laterally between the Dash 8 and the second formation. The tower controller² had not established a visual separation standard between the aircraft at the time the Dash 8 pilots received the RA. There was an infringement of separation standards.
At about 1539:35^3,4 Eastern Daylight-saving Time, the pilots of an Israel Aircraft Industries Limited 1124A Westwind (Westwind) aircraft, that had been participating in a military training exercise, contacted the tower controller and advised that they were 7 NM to the north of Williamtown Airport, tracking to join the circuit on a left base leg for runway 12. At that time, the first formation of Hornet aircraft had passed the initial point⁵ (Figure 1) for runway 12, and the Dash 8 was in an early right downwind position.
At 1540:10, the tower controller advised the pilots of the Dash 8 to conduct orbits to the south-west of the airfield at 2,500 ft. However, the tower supervisor assessed that the Dash 8 could continue on the downwind leg and advised the tower controller to cancel the orbit instruction. At 1540:20, the tower controller complied and instructed the pilots of the Dash 8 to continue on the downwind leg. The tower supervisor had intended to position the Dash 8 behind the first formation in the landing sequence.

Figure 1: Generic depiction of a military stream landing circuit showing the location of the initial point (left circuit depicted)

(adapted from the Manual of Air Traffic Services Pt 3 s3, effective 10 June 2004)

At 1541:10, the tower controller instructed the pilots of the Dash 8 to make a visual approach and to track for right base. At 1541:20, the tower controller instructed the pilots of the Westwind to join the circuit via the upwind leg. In response to that instruction, the pilots of the Westwind advised the tower controller that the aircraft was 'minimum fuel'⁶. The tower controller did not respond immediately to that broadcast and the Westwind continued the approach via left base. At about 1541:30, the radar data showed that the Dash 8 had already commenced the turn onto the right base leg of the circuit. At that time, the Westwind was established on left base. The Westwind pilots had positioned their aircraft behind the first formation in the landing sequence. In order to separate the Dash 8 and the Westwind, the tower controller instructed the pilots of the Dash 8 to continue on the downwind leg and that they were now to follow the Westwind.

At 1542, the tower controller advised the pilots of the Dash 8 that they could turn onto the base leg, when ready. At that time the aircraft was close to the airspace boundary separating tower and approach areas of responsibility, about 6.9 NM north-west of the airport.

At 1542:20, the approach controller provided traffic information, on the Dash 8, to the pilots of the second formation. A review of the recorded radar data showed that, at that time, the second formation was about 3 NM behind the Dash 8. Although the investigation was unable to accurately determine the vertical distance between the aircraft, from that radar data, it appeared that there was about 100 ft between the second formation and the Dash 8 when the approach controller provided traffic information to the pilots of the second formation. The pilot of the lead aircraft in the second formation advised the approach controller that he could see the Dash 8.

The recorded radar data also showed that the altitude of the Dash 8 increased from 2,500 ft on late downwind, to 2,900 ft as the aircraft commenced the base turn, before descending in response to the TCAS RA. The Dash 8 subsequently continued to descend for a landing. At 1542:50, the second formation passed abeam the Dash 8, when the Dash 8 was about to commence the turn onto the final approach leg. At that time, there was 0.6 NM laterally between the aircraft, and the Dash 8 was 300 ft vertically below the second formation. The pilots of the Dash 8 advised the tower controller that they had received an RA and that they were on a 'TCAS descent'.

At 1543, the pilots of the second formation called the tower controller and advised that they were at the right initial⁷ position. The tower controller then realised that the second formation was inbound and provided the pilots of the Dash 8 with traffic information on that formation.

Minimum fuel

In accordance with the Royal Australian Air Force (RAAF) Williamtown Standing Instructions, the Westwind was considered to be a military aircraft while participating in military exercises.

The copilot of the Westwind notified the tower controller that the aircraft was 'minimum fuel' when the aircraft was on a left base position for runway 12. The pilot in command of the Westwind later reported that the aircraft was not 'minimum fuel', and that the copilot had mistakenly made the 'minimum fuel' radio broadcast. The operator of the Westwind advised that the declaration of minimum fuel in that aircraft meant there was '…900 [pounds] or less total fuel remaining at the Base Turn Point when in the circuit, at an airport where a landing is assured'.

Air traffic control separation standards and procedures

Control of aircraft in the Williamtown Airport terminal area was provided by a tower controller using visual procedures and vertical separation, and by an approach controller using radar and procedural separation standards, in accordance with the Manual of Air Traffic Services⁸ (MATS) and local procedures. Coordination of control responsibilities was required between the approach controller and the tower controller in accordance with local procedures.

The required minimum vertical separation standard between the Dash 8 and other aircraft operating in the Williamtown airspace was 1,000 ft.

In relation to the provision of aircraft separation, the MATS 4.1.1.4 stated that:

Tactical Separation Assurance places greater emphasis on traffic planning and conflict avoidance rather than conflict resolution. This is achieved through:

1. the proactive application of separation standards to avoid rather than resolve conflicts;
2. planning traffic to guarantee rather than achieve separation;
3. executing the plan so as to guarantee separation; and
4. monitoring the situation to ensure that plan and execution are effective.

The tower controller cleared the pilot of the Dash 8 for further descent on a visual approach when the aircraft was in a late downwind position. A visual approach authorised the pilots to continue descent visually for a landing. A review of the recorded radar data showed that the Dash 8 maintained 2,600 ft for about 1.5 minutes on the downwind leg of the circuit. It reached a minimum altitude of 2,500 ft, on descent, when the aircraft was on a late downwind position, and climbed to 2,900 ft as it turned onto the base leg.

The Aeronautical Information Publication (AIP) advised pilots that they must report to ATC 'when the aircraft has left a level at which level flight has been conducted in the course of climb, cruise or descent'. The pilot in command of the Dash 8 did not recall climbing the aircraft from 2,500 ft on the downwind leg to 2,900 ft on the base leg of the circuit.

Approach control

At Williamtown Airport, the approach controller was responsible for providing an air traffic control service between instrument flight rules (IFR) category aircraft in accordance with the MATS and local procedures. That included ensuring that a separation standard existed between arriving IFR aircraft, and providing an orderly flow of arriving aircraft.

There was an approach controller and a supervisor rostered in the Williamtown approach control unit at the time of the occurrence. Both positions were staffed by an appropriately rated military air traffic controller (ATC). The approach controller had about 6 years experience as an ATC, and had been rated in the approach radar position at Williamtown Airport for 6 months. The approach supervisor was responsible for the supervision of the approach control unit at Williamtown Airport. He had considerable experience as an ATC, and had held a rating in approach control at Williamtown Airport for about 18 months.

A review of the recorded radar data showed that, at the time the approach controller cleared the pilots of the second formation to descend to 3,000 ft, the second formation was approximately 27 NM from the airport, with about 32 NM to fly to land. Had the pilots of the Dash 8 not been instructed to extend the downwind leg, the Dash 8 would have had about 6 to 8 NM to fly to touch down. The assignment of 3,000 ft to the pilots of the second formation did not provide either a vertical separation standard, or separation assurance, between the second formation and the Dash 8 in the circuit. The approach controller was not concerned about the separation between the Dash 8 on the downwind leg, and the second formation on descent to 3,000 ft, because of the distance the second formation was from the airfield at the time the approach controller issued the descent clearance.

The normal circuit direction at Williamtown Airport, on runway 12, was right. Military aircraft would track from the initial point along the dead side⁹ of the circuit and turn right, into the circuit, once the pilot saw the other traffic operating in the circuit (see Figure 1). The approach controller cleared the Westwind to enter the circuit via a non-standard left base leg and to descend on a visual approach.

The tower controller was required, by local procedures, to advise the approach controller when the Dash 8 pilots were cleared to descend on a visual approach.

On receipt of that advice, the approach controller removed the Dash 8's flight progress strip¹⁰ from the flight progress board¹¹. Although the aircraft was still visible to the approach controller on the situation data display (SDD)¹², the potential for an infringement of separation standards was no longer presented to the approach controller on the flight progress board. The approach controller later reported that the flight progress strip was removed from the board because there was an expectation that the second formation would remain clear of the Dash 8 in the circuit.

Tower control

The tower cabin was equipped with an SDD that provided the tower controller with the same display of air traffic that was provided to the approach controller. The MATS addressed the use of tower radar in an aerodrome control service. It stated that the tower radar display was available for the determination of the altitude, position or tracking of an aircraft to establish or monitor separation. However, the MATS also stated that:

…the use of the tower radar should not impinge upon an aerodrome controller's primary function of maintaining a visual observation of operations on and in the vicinity of the aerodrome.

There were three operational control positions established in the control tower; a supervisor position, a tower control position and a surface movement control position. Each position was staffed by an appropriately rated military ATC. The supervisor and the tower controller each had 18 months tower control experience. The control tower was also a training environment at the time of the occurrence. There was a controller-under-training in each of the three control positions. Each rated military controller, in each of the positions, was also a qualified training officer.

The supervisor was responsible for airspace management and operations on the airport. The supervisor had the authority to assess and amend the decisions of the tower controller and the surface movement controller if required. Unless the tower controller considered that such intervention compromised safety, the tower controller was obliged to comply with the decisions of the supervisor.

The first formation joined the circuit on a right crosswind leg on descent from 1,500 ft. Once the tower controller was able to apply a visual separation standard between the Dash 8 and that formation, the tower controller instructed the pilots of the Dash 8 to descend on a visual approach.

The tower controller was also required to notify the approach controller of any aircraft that were extending towards the aerodrome traffic zone (ATZ) lateral boundary which was the lateral boundary of tower airspace¹³. Neither the tower controller nor the supervisor advised the approach controller that the Dash 8 was extending downwind, and would be turning onto the base leg in the vicinity of the lateral boundary of the ATZ. The approach controller was not expecting to see the Dash 8 in that position. The approach controller observed, on the SDD, the Dash 8 turning onto the base leg of the circuit in the vicinity of the lateral boundary of the ATZ, and in the vicinity of the second formation.

The approach controller immediately provided traffic information to the pilots of the second formation about the Dash 8, but could not provide traffic information to the Dash 8 pilots as they were operating on the tower frequency.

The tower controller later reported that he originally intended to instruct the pilots of the Dash 8 to remain in the downwind position at 2,500 ft because it enabled him to better regulate the circuit traffic, especially given that he was instructing a controller-under-training at the time.

Instructing pilots to maintain 2,500 ft on the downwind leg was a common practice at Williamtown Airport. The AIP En Route Supplement Australia (ERSA) advised that all civil aircraft operating at Williamtown Airport were required to carry 30 minutes holding fuel. The tower controller later reported that that holding fuel enabled Williamtown air traffic control the flexibility to hold civil aircraft for up to 30 minutes, if necessary, for sequencing with arriving military aircraft.

Australian Defence Air Traffic System (ADATS)

Air traffic controllers at Williamtown Airport used the Australian Defence Air Traffic System (ADATS) to control aircraft operating within the Williamtown airspace. The ADATS associated a flight plan to an allocated transponder code¹⁴ and displayed that information to the controller as a data block, attached to the aircraft track symbol, on the SDD.

The data block could either be a full or limited data block. The full data block was white and included the call sign, altitude and radar derived ground speed, of airborne aircraft equipped with a serviceable transponder. It could also include other control information entered by a controller. A code and flight plan remained associated for a predetermined period of time depending on the nature of the flight. Once that time expired, the code/flight plan association terminated and the data block presented to the controller became a limited data block. The limited data block format did not display the call sign, and the colour of the data block changed from white to green. The limited data block format displayed an aircraft's allocated transponder code, altitude and radar derived ground speed.

The colours allocated to the track symbol and data block indicated the relevance of that aircraft to controllers. A green data block normally indicated that the aircraft was no longer of concern to the controller, as the flight plan was no longer active. The data block and track symbol colours assisted controllers with situational awareness.

The information displayed to the approach controller was also displayed to the tower controllers on the tower SDD. All information on relevant inbound, locally-based, military aircraft was displayed in the aircraft data block, including sequencing and tracking information. In accordance with local procedures, while a flight plan was associated with a specific transponder code, there was no requirement for the approach controller to provide voice coordination to the tower controller.

That applied to locally-based, military aircraft, as that information was available on the tower SDD. The tower controller was required to scan the SDD to determine the sequence and tracking details of arriving locally-based military aircraft. Tower controllers relied on the accuracy of the information presented in the data block, including the colour and sequencing instructions, to assist them in determining an estimated time of arrival, the arrival sequence and the inbound route of each aircraft.

Controllers reported that occasionally the code/flight plan association terminated while aircraft were still airborne. In those circumstances, in accordance with local procedures, the approach controller was required to use voice coordination to advise the tower controller about relevant inbound aircraft. The tower controller would not necessarily detect an inbound aircraft on the SDD if the code/flight plan association had terminated, unless voice coordination was received from the approach controller.

The code/flight plan association for the second formation terminated as the formation tracked to the circuit area and the data label changed colour from white to green. The approach controller reported that, as the termination occurred close to the circuit area, the tower controller would already have been aware that the formation was inbound. As a result, no voice coordination was provided to the tower controller.

Meteorological information

The weather was reported as fine and clear and was not considered to have been a factor in the occurrence.

1. Only those investigation areas identified by the headings and subheadings were considered to be relevant to the circumstances of the occurrence.
2. A tower controller employed by the Department of Defence provides a similar air traffic control service as a civil aerodrome controller.
3. The 24-hour clock is used in this report to describe the local time of day, Eastern Daylight-saving Time, as particular events occurred. Eastern Daylight-saving Time was Coordinated Universal Time (UTC)+ 11 hours.
4. Due to the limitations with the audio recording, all times are accurate to within about +/- 5 seconds.
5. The initial point for runway 12 at Williamtown Airport was located about 4 NM from the threshold of runway 12 along the extended centreline of taxiway Alpha, at 1,500 feet above mean sea level.
6. This phrase is used to advise air traffic control that the pilot requires priority for landing based on the amount of fuel remaining, calculated at a particular stage of flight (Manual of Air Traffic Services, pt 10, effective 9 June 2004).
7. The left, right and straight initial positions are 30 seconds prior to the initial point with wings level.
8. The Manual of Air Traffic Service is a joint civil/military publication used by Department of Defence and Airservices Australia air traffic controllers.
9. The dead side of the circuit is the side of the airfield or active runway, opposite to that of the circuit pattern in use, and from which arriving aircraft joining the circuit.
10. A flight progress strip is a thin cardboard strip used to record flight data relating to control of an aircraft.
11. A flight progress board is a piece of equipment used to display flight progress strips. Controllers use the information on the flight progress board to assist in managing the traffic situation.
12. The situation data display was an electronic display of radar derived information that depicted the positions and movements of aircraft.
13. The ATZ is that airspace within 5 NM of the tactical air navigation equipment ground based navigation aid, over land, from ground level to 1,500 ft above mean sea level. At Williamtown Airport, the stream landing circuit pattern (see Figure 1) is contained entirely within the ATZ.
14. A transponder is a receiver/transmitter which will generate a reply signal upon proper interrogation, in this case, of a signal generated by a ground based transmitter/receiver.

On 31 January 2005, a de-Havilland Canada Dash 8-202 (Dash 8) aircraft that was inbound to Williamtown Airport, NSW, on a scheduled passenger service from Brisbane, Queensland, passed 0.6 NM laterally and 300 ft vertically by the second of two formations of two McDonnell Douglas Corporation F/A-18 (Hornet) aircraft that were inbound to Williamtown Airport after a training exercise. As the Dash 8 turned onto the base leg, the second formation was about 6 NM north-west of Williamtown Airport, at 2,900 ft above mean sea level. The pilots of the Dash 8 descended in response to a traffic alert and collision avoidance system resolution advisory (RA) they received on that formation. The approach controller did not provide the required separation standard of 1,000 ft vertically or 3 NM laterally between the Dash 8 and the second formation. The tower controller had not established a visual separation standard between the aircraft at the time the Dash 8 pilots received the RA. There was an infringement of separation standards.

The investigation found that the factors that contributed to the occurrence included:

• The approach controller did not assign an altitude to the second formation that provided a vertical separation standard between the second formation and the Dash 8
• The tower supervisor advised the tower controller to cancel an instruction to the Dash 8 pilots to orbit on the downwind leg of the circuit at 2,500 ft, and to continue on the downwind leg of the circuit
• The tower controller did not notify the approach controller that the Dash 8 was extending towards the lateral boundary of tower airspace
• The pilots of a Westwind incorrectly notified the tower that their aircraft was 'minimum fuel' and did not join the circuit via the upwind leg as instructed by the tower controller.

FINDINGS

During the flight, the amount of generated VIA BITE data exceeded the memory size. As a result, BITE data from the event that initiated the FMS problem was overwritten and lost.

The available BITE data showed that FMC 2 was unable to sequence the ‘400 ft course to altitude’ leg associated with the SWIFT SIX SID. Eventually, FMC 2 performed a software reset but was unable to recover and latched.

A similar progression then occurred for FMC 1 but, in accordance with its design, FMC 1 did not latch and was available for use but with the flight plan information cleared.

ANALYSIS

The FMS performance reported by the crew was consistent with FMC 2 performing a progressive series of resets before it latched. A similar progression of resets then occurred for FMC 1 but, in accordance with its design, it did not latch and was available for use but with the flight plan information cleared. During the resetting process, the FMS response would have been confusing to the crew and consistent with the crew’s observation of the ‘FMS locking us out’.

With FMC 2 latched, the MENU page would have been displayed on the copilot’s multi-function control and display unit (MCDU) but with the FMC 2 prompt missing from the top left data field. The standby navigation/radio (STANDBY NAV/RAD*) prompt would also have been displayed on the MCDU and ‘MAP FAIL’ displayed on the copilot’s navigation display. Once the resetting was completed, then an ILS frequency could be tuned using the STANDBY NAV/RAD page on either the pilot in command’s (PIC) or copilot’s MCDU.

The PIC was the handling pilot during the flight. Normally the PIC’s MCDU will interact with FMC 1 and the copilot’s MCDU will interact with FMC 2. With FMC 2 latched, it was necessary for the copilot to change his source select switch to ‘FO ON 1’ to access FMC 1.

During the investigation the VIA manufacturer advised that no other FMS problems of this nature had been reported.

The Boeing 717-200 was taxiing at Cairns Qld for a scheduled service to Brisbane Qld. As part of the preparation for the flight, the crew had entered flight plan details into the aircraft's flight management system (FMS). While taxiing, due to intermittent rain showers at Cairns, the 717 crew then programmed the FMS with wet runway speed figures for take-off.

The crew reported that late in the take-off roll the manually entered wet speeds were lost from the airspeed tape on the primary flight display and FMS-generated speeds were displayed. At rotation 'MAP FAIL' appeared on both navigation displays.

The investigation found that flight management computer (FMC) 2 was unable to sequence the '400 ft course to altitude' leg associated with the SWIFT SIX standard instrument departure. Eventually, FMC 2 performed a software reset but was unable to recover and became unavailable for use by the crew. A similar progression then occurred for FMC 1 but, in accordance with its design, FMC 1 remained available for use but with the flight plan information cleared.

Eventually the crew were able to enter the instrument landing system frequency, but FMS operation did not appear to be reliable. The aircraft was radar vectored for a return to Cairns while maintaining visual meteorological conditions. The crew conducted a visual approach to runway 15 and the aircraft landed 32 minutes after take-off.

1. Meteorological conditions were conducive to wind shear, mechanical turbulence or a combination thereof.
2. The pilot took off in a crosswind that exceeded the limitations specified in the Pilots Operating Handbook.

The environmental conditions at the time of the accident required the pilot to take particular account of the prevailing sea conditions and the wind direction and speed, when selecting the area for, and direction of, the take-off. This led to the pilot making a compromise that placed emphasis on an area with a more favourable sea state rather than directly into the prevailing wind.

The local effects of the terrain gave the impression to the pilot that the wind at surface level in the area selected for the take-off was from the north-north-east. Therefore, he assessed that that wind direction was suitable for the take-off. However, it is likely that the aircraft encountered a crosswind during the take-off that exceeded the limitations in the Pilots Operating Handbook (POH). It was also likely that wind shear or mechanical turbulence, or a combination of both these effects, was encountered by the pilot shortly after take-off. At the point where the angle of bank of the aircraft exceeded 45 degrees, it is likely that the aircraft stalled causing it to strike the water.

The pilot reported that he was able to exit the aircraft quickly because of his previous underwater escape training. The Australian Transport Safety Bureau encourages all operators in this environment to ensure that their flight crews have completed similar training. The actions of the rear seat passenger were significant in enabling the remaining occupants to exit the aircraft.

The pilot and passengers did not have the time to retrieve their life jackets from under their seats before exiting the aircraft. This was also the case in the floatplane accident in Tasmania in 2001 (BO/200105932). Although the carriage of life jackets and the stowage of them below each of the seats was in accordance with Civil Aviation Order (CAO) 20.11 parts 5.1.4 and 5.1.5, the wearing of life jackets was not required by CAO 20.11 part 5.1.8, and as a consequence, their availability was not assured after the occupants of the floatplane had exited the aircraft into the water.

The lack of time available to retrieve and don life jackets in the event of an accident when operating close to, or on the water, has the potential to adversely affect the survivability of aircraft occupants after they have exited an aircraft. As highlighted in Federal Aviation Administration Advisory Circular (AC) 91-69A, it is extremely difficult for a person to don a life jacket when they are already in the water, and practically impossible to do so if the person is injured.

At 1735 eastern summer time on 20 January 2005, a Cessna Aircraft Company A185F floatplane, registered VH-SBH, with one pilot and three passengers on board was taking off on a water departure for a charter flight from Rose Bay aircraft landing area (ALA) to Palm Beach, NSW. Shortly after becoming airborne, the aircraft rolled 45 degrees to the left causing the left wing to strike the water. The aircraft became inverted and was substantially damaged. The four occupants escaped with minor injuries.

The pilot had positioned the floatplane to the eastern side of the ALA, approximately 200 m from the shoreline and to the west of a headland, to achieve more favourable sea conditions for a take-off to the north-north-west. The pilot reported that the wind direction was 010 degrees M at a speed of 20 kts. The intended take-off path ran approximately parallel to the headland in a direction of 350 degrees M.

The pilot reported selecting 20 degrees of flap for the take-off. As the aircraft was about to leave the surface, he selected 30 degrees of flap. This technique was used to help get the aircraft off the surface of the water quickly in difficult sea and/or weather conditions. He also reported that the aircraft took longer than he expected to reach take-off speed. The aircraft became airborne at 45 to 50 kts and he then selected 20 degrees of flap. At approximately 30 ft above the water, the aircraft commenced an uncommanded left roll that he was able to correct with full right aileron input. The aircraft then commenced a second uncommanded left roll that he was unable to correct with control inputs. The pilot, passengers and witnesses, all reported that the aircraft rolled more than 45 degrees to the left before the left wing struck the water.

The floatplane came to rest inverted and shortly after the cabin became submerged. The pilot reported that he had completed Helicopter Underwater Escape Training (HUET) previously, and that he thought that assisted him to exit the cabin quickly through the pilot's door, located on the left of the cabin. The passenger in the copilot's seat, located on the right of the cabin, was momentarily disorientated, but managed to undo his seat belt while the passenger in the middle row was attempting to locate and undo his seatbelt. The rear seat passenger was able to swim towards the front passenger and reported kicking open a door with her foot before pushing the front passenger out of the aircraft. She then returned to the middle row passenger and unfastened his seat belt buckle before pushing him out of the aircraft and then exiting the submerged cabin herself. One passenger reported that he was initially disoriented after the aircraft entered the water. In addition, given the rapid nature of the event and the need to exit the inverted cabin quickly, the passengers did not retrieve the life jackets which were stowed underneath their seats. It was likely that all passengers exited the floatplane via the pilot's door, because the co-pilot's door was still locked closed when the aircraft was recovered.

The floatplane stayed inverted with its floats remaining buoyant. After exiting the aircraft, the passengers were picked up by a passing boat. The pilot remained with the aircraft and secured it to a boat.

The load chart for the flight showed that the aircraft was within weight and balance limitations. The pilot was appropriately licensed and endorsed for the operation and was experienced in floatplane operations in Sydney Harbour. The aircraft was capable of normal operations before flight and there were no known maintenance issues.

A Bureau of Meteorology (BoM) report of the weather in Sydney Harbour at the time of the accident, showed that the prevailing wind around the time of the accident was from the north-east, averaging 26 to 29 kts, with gusts reaching 37 kts. The report also suggested that:

…in considering the wind shear that would have been experienced by a plane taking off from Rose Bay, the sheltering effect of the surrounding topography, especially the shielding of Rose Bay from north easterlies by the southern headland of Sydney Harbour, needs to be taken into account. It is conceivable that in passing from the relatively sheltered inshore waters of Rose Bay to a more exposed location, either through ascent or forward motion or both, that significant wind shear may have been experienced.

The pilot advised that he used a number of cues to determine the wind velocity, particularly the orientation of moored boats and flags, the BoM forecast and the water conditions.

Mountain waves and their turbulence can occur downwind of any obstacle, including an isolated hill a few hundred feet high. If the wind at the altitude of the top of the obstacle is 20 kts or more, there will be noticeable wave turbulence and significant downdrafts. This turbulence will be greatest in the rotor zone in the lee of the obstacle and will be at a maximum at about the same altitude as the top of the obstacle.¹

The company ALA register notation for Rose Bay warned that 'Dumping will be encountered in winds over 20 kts from the North-East, South and West'. The significant downdrafts described in the previous paragraph are what the operator's ALA register referred to as 'dumping'.

A fact sheet on mountain wave turbulence that accompanied Australian Transport Safety Bureau (ATSB) report BO/200104092 into an accident involving mechanical turbulence stated in part that:

In addition to generating turbulence that has demonstrated sufficient ferocity to significantly damage aircraft or lead to loss of control, the more prevailing danger to aircraft in the lower levels in Australia seems to be the effect on an aircraft's climb rate. General Aviation aircraft rarely have the performance capability sufficient to enable the pilot to overcome the effects of a severe downdraft generated by a mountain wave, or the turbulence or the windshear² generated by the rotor.

The Pilots Operating Handbook (POH) for the Cessna 185 indicated that the stalling speed in a 20 degree flap configuration, at a mid-range centre of gravity, was 55 kts. The POH also indicated a maximum demonstrated crosswind velocity for take-off and landing of 13 kts. The investigation determined that the crosswind for the accident flight would have been between 19 and 24 kts.

In December 2001, the ATSB investigated an accident involving a floatplane in Tasmania where the occupants had insufficient time to don life jackets before exiting the aircraft (see ATSB report BO/200105932). That accident investigation highlighted that regulations governing the use of life jackets, do not reflect the operational realities of exiting from an inverted submerged cabin.

Civil Aviation Order (CAO) 20.11 part 5.1.4 stated that:

Amphibious aircraft when operating on water, helicopters equipped with fixed flotation equipment when operating on water, and all seaplanes and flying boats on all flights shall be equipped with:
(a) 1 life jacket for each occupant; and
(b) an additional number of life jackets (equal to at least one-fifth of the total number of occupants) in a readily accessible position near the exits.

CAO 20.11part 5.1.4 stated that:

Life jackets shall be so stowed in the aircraft that 1 life jacket is readily accessible to each occupant and, in the case of passengers, within easy reach of their seats.

CAO 20.11 part 5.1.8 stated that:

Where life jackets are required to be carried in accordance with paragraph 5.1.4 each occupant of a single engine aircraft shall wear a life jacket during flight over water when the aircraft is operated beyond gliding distance from land or water, as appropriate, suitable for an emergency landing. However, occupants need not wear life jackets when the aircraft is taking off or landing at an aerodrome in accordance with a normal navigational procedure for departing from or arriving at that aerodrome, and occupants of aeroplanes need not wear life jackets during flight above 2 000 feet above the water.

Federal Aviation Administration Advisory Circular (AC) 91-69A contained recommendations and revised information for the safe operation of seaplanes. The AC stated that:

Life jackets in sealed pouches can be awkward to remove and don in a flooded aircraft. When a survivor attempts to put on a jacket in the water, it may be difficult to find and fasten its straps and hooks. It would take considerable effort to accomplish the combined maneuver [sic] of pulling a lifejacket over one's head while in the water trying to stay afloat. If a life preserver is not worn before flight, it is practically impossible for a survivor with an injured arm, for example, to don the life preserver in time for it to be effective for survival. Wearing an uninflated TSO C13f life preserver at all times in the seaplane and inflating it only after exiting the seaplane would seem to be the best protection.

Furthermore, the AC stated that after a seaplane accident:

and especially while submerged inverted in water, the passengers are likely to become disoriented and panic.

It also stated that:

Maneuvring [sic] while holding flotation devices can also be disorienting because it occupies the hands, making swimming or treading water difficult.

Additionally the AC stated in Section 1.b. (1)

For-hire operators must use FAA-approved PFD's. A PFD should be worn by each occupant while on the seaplane.

1. Modern Airmanship, Eighth Edition, Van Nostrand Reinhold Company, New York, 1999.

2. A change of wind velocity with distance along an axis at right angles to wind direction, specified vertically or horizontally. Recognised as an extremely dangerous phenomenon because encountered chiefly at low altitude (in squall or local frontal systems) in approach configuration at speed where it makes sudden and potentially disastrous difference to airspeed and thus lift.

The pilot had experienced difficulty with securing the locker door on previous occasions as it could not be placed into a position that was flush with the fuselage. This created a potential for air flowing under the nose locker door to open it. Damage to the recovered components was not consistent with failure of the lock mechanism; however, failure of the other lock may not be discounted. Given the difficulty in securing the nose locker door, it is likely that it had not been properly secured prior to the occurrence flight.

The main cabin door/locker door warning annunciator was continuously illuminated and was therefore no longer effective as a warning. Consequently, the operational safety intent of the original door warning system design had been negated by the engineering for the modified door.

On 21 January 2005 at about 0830 Eastern Daylight-saving Time, a de Havilland Canada DHC6-200 Twin Otter aircraft, registered VH-JEA, was engaged in commercial skydiving operations at Wilton, NSW, with one pilot and 12 parachutists on board.

The left main landing gear actuator's thrust bearing was very likely incorrectly reinstalled during the recent maintenance of that component. As a result, increased torque was required to rotate the screw jack actuator in order to retract the landing gear. That increased torque most probably tripped the landing gear electric motor's 60 amp circuit breaker during the flight immediately prior to the accident flight. However, in that instance, the pilot was able to manually extend the landing gear.

The torque applied to the screw jack actuator during the functional test before the accident flight was probably below that necessary to trip the 60 amp circuit breaker. In addition, that maintenance action failed to identify the incorrectly installed thrust bearing, and underlying increased torque required to rotate the actuator. When the pilot attempted to retract the landing gear during the accident flight, the increased torque resulting from the incorrectly installed thrust bearing, together with air loads would have combined to overload the systems. The result was that the landing gear electric motor's circuit breaker tripped, and the pilot was unable to either electrically or manually extend the landing gear.

The puncture of the aircraft's fuel tank increased the risk of a post-impact fire, or of another fuel-related hazard during the landing and subsequent emergency disembarkation. Despite the lack of a declaration of a Local Standby condition, the action by the Rescue and Fire Fighting services to board their vehicles facilitated a rapid emergency response.

At about 1512 Western Standard Time on 18 January 2005, a Beech Aircraft Corp B200 (Super King Air) aircraft, registered VH-SGT, sustained damage when its main landing gear collapsed on touch down on runway 24 at Perth Airport, WA. The aircraft had earlier departed the aerodrome on a charter flight with one pilot and seven passengers on board.

The pilot had elected to return to the aerodrome after detecting a problem during the retraction of the aircraft's landing gear. He attempted to manually extend the landing gear but was unable to confirm that the landing gear had locked in position for the subsequent precautionary landing. The main landing gear collapsed as the aircraft touched down.

In the absence of the declaration of a Local Standby condition by either the pilot in command or the Air Traffic (ATS) services personnel, the on-airport Rescue and Fire Fighting services (RFF) were not placed in that condition of readiness for the landing. However, on receiving advice from ATS of the circumstances of the aircraft's return for landing, the RFF services personnel boarded their vehicles in preparation for a possible emergency response.

Examination of the aircraft landing gear by the aircraft operator revealed an incorrectly installed thrust bearing in the hydraulic actuator for the left main landing gear. The result was that the axial loads normally carried by the thrust bearing were transferred to the actuator's pinion gears which fractured under abnormal operational loads. That damage seized the actuator and prevented the manual extension of the aircraft's landing gear by the pilot.

ANALYSIS

The investigation concluded that there was no infringement of separation standards, because the Albury aerodrome controller reported that he maintained a visual separation standard, in accordance with the Manual of Air Traffic Services (MATS), between the Saab and the Dash 8, until the Hume controller advised that he had 'just over 7 miles' between the two aircraft.

The Albury aerodrome controller did not establish a step-climb procedure between the two aircraft in accordance with the terms of the clearance as coordinated with the Hume controller. The aerodrome controller should have advised the Hume sector controller that he was unable to comply with the terms of that clearance. Both controllers could then have coordinated another mutually acceptable clearance before the aerodrome controller transferred control of the aircraft to the Hume controller. The establishment of a step-climb procedure would have ensured that a procedural separation standard continued to exist between the aircraft until such time as the Hume controller established a radar separation standard and accepted responsibility for the aircraft.

The Albury aerodrome controller was required to establish a procedural separation standard between the two aircraft and to have that standard in place before transferring the responsibility for separation to the Hume controller.

The aerodrome controller's use of visual separation technically complied with the separation provisions stated in the MATS for Albury tower procedural separation purposes. However, use of that procedure did not meet the Hume controller's requirements for procedural separation and would not have ensured that separation continued to exist in the event that the aerodrome controller lost sight of one or both of the aircraft. Furthermore, it did not demonstrate 'the proactive application of separation standards to avoid rather than resolve conflicts' as stated in the MATS.

The ability of a sector controller to apply a separation standard using radar may be influenced by factors such as the sector controller's workload, or a failure of an aircraft's transponder, for example. Therefore, aerodrome controllers cannot anticipate when a sector controller may be able to establish a radar separation standard. In the event that the sector controller could not establish a radar standard, the application of an appropriate procedural separation standard that could be used by both controllers would have ensured that separation continued to exist. Such a procedure would have complied with the separation assurance provisions of the MATS.

Technical adherence to the provisions of one separation standard may not guarantee that separation will continue to exist. In this circumstance, the aerodrome controller relied on being able to continue to apply an interpretation of visual separation between the two aircraft until he anticipated that the sector controller could separate the aircraft using radar. While only one separation standard needs to be applied for separation to exist, contingencies such as controller workload and other traffic might preclude the application of another form of separation before the minima of that one standard are infringed. The application of the tactical separation assurance provisions specified in the MATS should assist controllers to anticipate such contingencies and, in doing so, help avoid, rather than resolve, conflicts.

On 17 January 2005, at 0633 Eastern Daylight-saving Time, a Saab Aircraft Company AB SF-340B (Saab) departed Albury Airport on a scheduled passenger service to Sydney, NSW. The aircraft was being operated under the instrument flight rules (IFR). The crew had been authorised by the Albury Tower aerodrome controller to track via Yass on the 043 degree radial from the Albury very high frequency omni-directional radio range (VOR) navigation aid and to climb to flight level (FL) 170. At 0636, a de Havilland Canada DHC-8-102 (Dash 8) aircraft departed Albury Airport on a scheduled passenger service to Sydney, also under the IFR. The crew of the Dash 8 were issued with a clearance by the aerodrome controller to track via the 055 degree radial from the Albury VOR and to climb to FL200.

Aviation Safety Recommendations

| Air Safety Recommendation R20050010 | Air Safety Recommendation R20050011