Time Out
16th Mar 2004, 23:33
At approximately 1840 Eastern Standard Time on Monday 29 July 2002, two Cessna Aircraft Company 172Rs, registered VH-CNW and VH-EUH, collided while on short final approach to runway 17 left (17L) at Moorabbin airport, Victoria. The two aircraft became entangled, with CNW on top of EUH. The entangled aircraft impacted the runway and came to rest after sliding a short distance along the runway surface.
The instructor and student pilot of EUH were conducting night circuit training and the pilot of CNW, the sole occupant, was conducting night circuits. Both aircraft were using runway 17L. The instructor and student pilot of EUH were able to exit their aircraft before fire engulfed both aircraft. The pilot of CNW was fatally injured.
Both aircraft were based at Moorabbin airport. The Moorabbin Air Traffic Control Tower was not in operation at the time of the accident and mandatory broadcast zone (MBZ) procedures were in use, under which pilots are required to:
See and avoid other aircraft,
Carry a serviceable radio, and
Make mandatory radio broadcasts when commencing to taxi for take off, when entering a runway for take off, prior to entering an MBZ when inbound or transiting and when inbound and joining the circuit.
Six aircraft were operating in the MBZ at the time of the accident. All were being flown by pilots who held a commercial pilot licence or some higher qualification.
The mandatory broadcast procedures in an MBZ provide a basic alert to assist pilots to see and avoid other aircraft, and can be supplemented by additional discretionary broadcasts. A mandatory broadcast may contain insufficient information to enable pilots to see-and-avoid other aircraft, or to enable them to make a meaningful assessment of the location of other aircraft. The pilots of CNW and EUH made all the relevant mandatory broadcasts. They also made a discretionary broadcast at about the time they were established on the base leg of the circuit. Those broadcasts did not effectively alert either pilot to the collision potential with the other aircraft.
Even though the two aircraft were of the same type and were operating at similar speeds in the circuit, radar data indicated that the pilots of EUH conducted a wider circuit than the pilot of CNW. The EUH circuit would have taken approximately 7 minutes to complete, whereas the pilot of CNW conducted a circuit that would have taken approximately 4.5 minutes to complete. Both circuit dimensions were within the range of circuit dimensions that were being conducted by other pilots at the time, and were not considered by the investigation to be contrary to procedures. While the dimensions of the circuits flown by the two accident aircraft were not unusual, the different circuit dimensions, and the consequent difference in the elapsed time, removed the natural spacing that would have typically resulted from the difference in take-off times. In the absence of any other defence or action, the different circuit dimensions led to the two aircraft converging on the final approach leg of the circuit. Neither of the pilots involved in the accident was aware of the impending collision.
The investigation identified the following significant factors:
The different circuit dimensions negated the natural spacing provided by the difference in takeoff times, even though both EUH and CNW were the same aircraft type and were operating in the circuit at similar speeds.
None of the pilots involved in the accident saw the other accident aircraft in sufficient time to enable either of them to avoid the collision.
The broadcasts made by the pilots did not assist their situational awareness.
Additionally, the investigation found deficiencies in the risk management process associated with the reduction in the Moorabbin airport air traffic control tower hours of operation. It could not be determined whether the reduction in tower hours contributed to the accident.
An earlier report3 found that human performance limitations in the visual scanning ‘…process can reduce the chance that a threat [potentially conflicting] aircraft will be seen and successfully evaded. These human factors are not “errors” nor are they signs of “poor airmanship”. They are limitations of the human visual and information processing system which are present to various degrees in all pilots’.
In particular, the practice of routinely re-analysing the information on which decisions are made, especially in airspace where the potential for a traffic confliction is relatively high, might help compensate for those inherent human performance limitations of the human visual and information processing system.
While not required under MBZ procedures, prior to the accident, the flying school required its instructors and student pilots to make a base broadcast at the start of the base leg of the circuit. Subsequent to the accident, the flying school has amended the content of that broadcast. Instructors and student pilots are now required to append their perceived number in the landing sequence to the base broadcast.
In September 2002, Airservices Australia approved a plan for an ongoing airport movement review outside tower hours for ATC towers that were not open 24 hours per day, which included Moorabbin tower, to monitor the need for an air traffic control service.
The Australian Transport Safety Bureau will be publishing a discussion paper in the next few weeks entitled ‘Review of mid-air collisions involving general aviation aircraft in Australia between 1961 and 2002’.
For the full report, see here (http://www.atsb.gov.au/aviation/pdf/200203449.pdf)
The instructor and student pilot of EUH were conducting night circuit training and the pilot of CNW, the sole occupant, was conducting night circuits. Both aircraft were using runway 17L. The instructor and student pilot of EUH were able to exit their aircraft before fire engulfed both aircraft. The pilot of CNW was fatally injured.
Both aircraft were based at Moorabbin airport. The Moorabbin Air Traffic Control Tower was not in operation at the time of the accident and mandatory broadcast zone (MBZ) procedures were in use, under which pilots are required to:
See and avoid other aircraft,
Carry a serviceable radio, and
Make mandatory radio broadcasts when commencing to taxi for take off, when entering a runway for take off, prior to entering an MBZ when inbound or transiting and when inbound and joining the circuit.
Six aircraft were operating in the MBZ at the time of the accident. All were being flown by pilots who held a commercial pilot licence or some higher qualification.
The mandatory broadcast procedures in an MBZ provide a basic alert to assist pilots to see and avoid other aircraft, and can be supplemented by additional discretionary broadcasts. A mandatory broadcast may contain insufficient information to enable pilots to see-and-avoid other aircraft, or to enable them to make a meaningful assessment of the location of other aircraft. The pilots of CNW and EUH made all the relevant mandatory broadcasts. They also made a discretionary broadcast at about the time they were established on the base leg of the circuit. Those broadcasts did not effectively alert either pilot to the collision potential with the other aircraft.
Even though the two aircraft were of the same type and were operating at similar speeds in the circuit, radar data indicated that the pilots of EUH conducted a wider circuit than the pilot of CNW. The EUH circuit would have taken approximately 7 minutes to complete, whereas the pilot of CNW conducted a circuit that would have taken approximately 4.5 minutes to complete. Both circuit dimensions were within the range of circuit dimensions that were being conducted by other pilots at the time, and were not considered by the investigation to be contrary to procedures. While the dimensions of the circuits flown by the two accident aircraft were not unusual, the different circuit dimensions, and the consequent difference in the elapsed time, removed the natural spacing that would have typically resulted from the difference in take-off times. In the absence of any other defence or action, the different circuit dimensions led to the two aircraft converging on the final approach leg of the circuit. Neither of the pilots involved in the accident was aware of the impending collision.
The investigation identified the following significant factors:
The different circuit dimensions negated the natural spacing provided by the difference in takeoff times, even though both EUH and CNW were the same aircraft type and were operating in the circuit at similar speeds.
None of the pilots involved in the accident saw the other accident aircraft in sufficient time to enable either of them to avoid the collision.
The broadcasts made by the pilots did not assist their situational awareness.
Additionally, the investigation found deficiencies in the risk management process associated with the reduction in the Moorabbin airport air traffic control tower hours of operation. It could not be determined whether the reduction in tower hours contributed to the accident.
An earlier report3 found that human performance limitations in the visual scanning ‘…process can reduce the chance that a threat [potentially conflicting] aircraft will be seen and successfully evaded. These human factors are not “errors” nor are they signs of “poor airmanship”. They are limitations of the human visual and information processing system which are present to various degrees in all pilots’.
In particular, the practice of routinely re-analysing the information on which decisions are made, especially in airspace where the potential for a traffic confliction is relatively high, might help compensate for those inherent human performance limitations of the human visual and information processing system.
While not required under MBZ procedures, prior to the accident, the flying school required its instructors and student pilots to make a base broadcast at the start of the base leg of the circuit. Subsequent to the accident, the flying school has amended the content of that broadcast. Instructors and student pilots are now required to append their perceived number in the landing sequence to the base broadcast.
In September 2002, Airservices Australia approved a plan for an ongoing airport movement review outside tower hours for ATC towers that were not open 24 hours per day, which included Moorabbin tower, to monitor the need for an air traffic control service.
The Australian Transport Safety Bureau will be publishing a discussion paper in the next few weeks entitled ‘Review of mid-air collisions involving general aviation aircraft in Australia between 1961 and 2002’.
For the full report, see here (http://www.atsb.gov.au/aviation/pdf/200203449.pdf)