The Boeing 737 was conducting a night VOR/DME approach to runway 05 at Adelaide Airport, which was under the influence of a low-level weather trough moving through the area. The co-pilot was the handling pilot.
The crew had reviewed the approach procedure and noted that due to strong northerly winds on the final approach track of 035 degrees, their expectation of sighting runway 05 through the co-pilot's window would be enhanced. At about 600 ft above ground level (AGL), the aircraft descended below the cloudbase into an area of poor visibility. The crew observed lights through the co-pilot's window which they believed to be on the aerodrome. They discontinued the instrument approach and tracked towards the lights, continuing to descend.
As the aircraft approached the lights, the pilot in command asked the co-pilot if he could see the runway precision approach path indicator (PAPI). The co-pilot replied that he could not. The pilot in command then checked his electronic horizontal situation indicator, which was operating in the VOR mode, and noted that the aircraft was well to the right of the inbound track of the approach. By this time, the aircraft had descended to 320 ft radar altitude. The crew immediately initiated a missed approach and obtained a clearance for an instrument landing system (ILS) approach to runway 23. The aircraft subsequently landed safely with a 6 kt downwind component.
At its minimum altitude, the aircraft had deviated 0.4 NM to the right of the runway centreline, at a distance of 1.1 NM from the runway threshold. The lights towards which the aircraft was tracking were south of the airport, probably on the Anzac Highway.
In the prevailing conditions of darkness and poor visibility, the crew's actions were consistent with an "error of expectancy". Such an error can occur when a person expects to perceive certain environmental cues and the strength of that expectation leads the person to misinterpret the environment, believing that those cues are present. In this case, the crew expected to see a lighted line feature aligned in a north-easterly direction through the co-pilot's window. What they saw fitted with their "mental model" of what they expected to see. At that point, the "real world" became more psychologically compelling than the information from the navigation instruments.
Expectancy is an unconscious phenomenon that is very difficult to overcome. Generally, it is more worthwhile to modify the environment or the task that led to the error, than to simply encourage people not to make such errors. Aircraft flying the final approach path of the runway 05 VOR/DME procedure, approach the aerodrome inbound along a track of 035 degrees M (south of the extended runway centreline). Aircraft do not intercept the extended centreline until the missed approach point at 1.5 NM by DME. Further, there are no approach lights for runway 05. Consequently, there are few visual cues to assist crews to intercept the extended runway centreline in darkness and/or poor visibility. Conversely, the nearby Anzac Highway is a prominent lighted line feature that can draw the crew's attention.
Other examples of crews misidentifying ground features for runways are:
16 June 1988, Airbus A300, Perth WA
The crew carried out a night VOR/DME approach for runway 03. The cloudbase was 800 ft. After the aircraft entered visual conditions, the crew were unable to visually identify the runway, which was not equipped with approach lighting. The crew had been confused by other ground lighting.
14 May 1989, Boeing 737, near Mackay Qld
The crew misidentified Broadsound Road for runway 14. The aircraft descended to 170 ft AGL on final approach before the crew became aware of the error.
In both of the above occurrences the crews carried out missed approaches after realising their errors.
Four respondents to a survey conducted by the Bureau of Air Safety Investigation in 1997 to obtain data for the Regional Airlines Safety Study, reported that the bright lights illuminating a railway marshalling yard adjacent to the final track for runway 10 could "drown out" the runway lights and create the illusion of a false runway.
As a result of this occurrence and the occurrences listed above, the Australian Transport Safety Bureau is investigating the issues surrounding approach lighting to non-precision approach runways. Any results from this investigation will be published in the Bureau's Quarterly Safety Deficiency Report.
|Date:||07 September 2000||Investigation status:||Completed|
|Time:||0632 hours CST|
|State:||South Australia||Occurrence type:||Depart/app/land wrong runway|
|Release date:||28 May 2001||Occurrence class:||Operational|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Canberra, ACT|