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.
Gladstone Qld
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.
