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Analysis

Summary

Standard company procedures required a monitored approach in the weather conditions prevailing at Darwin for the aircraft's approach and landing. The approach was conducted at night and in conditions of rain and reduced visibility.

The aerodrome controller had selected the runway 29 HIAL and HIRL to a higher intensity than recommended in MATS for the initial setting given the prevailing weather conditions. Although this selection assisted the crew to acquire the HIAL and HIRL at an earlier stage of the approach, the apparent intensity of those lights increased significantly as the aircraft approached the runway. The crew did not realise that the lights were too bright until the aircraft was passing overhead the HIAL and consequently, did not request a lower intensity selection.

The aircraft commenced deviating from the extended runway centreline about 7 seconds after the autopilot was disengaged and as the HIAL was starting to disappear from the pilot's view. Associated with this deviation were control inputs by the pilot in command, including a left rudder pedal command and a right wing down control wheel input that resulted in the aircraft entering a cross-controlled sideslip to the right as the aircraft approached the runway. These control inputs were not conventional for the environmental conditions.

The control inputs made by the pilot in command during the final stages of flight altered the aircraft's flight path across the ground and directly contributed to the aircraft's deviation from the runway centreline. The control wheel inputs for right roll resulted in the deployment of the right wing's flight spoilers during the final 70 ft of the descent. This increased the drag on the right wing, reduced the lift produced by that part of the aerofoil section and consequently, increased the rate of descent. The investigation could not determine the reason for the rudder and aileron inputs made by the pilot in command.

The data derived by kinematic analysis by the aircraft manufacturer was consistent with other available sources of environmental wind data.

The pilot in command did not detect the aircraft's increasing lateral displacement from the runway centreline. He considered that he had sufficient visual reference to complete the landing. However, during the final seconds prior to touchdown, it was possible that he encountered an abnormal situation where few reliable visual cues were available for determining the aircraft's position relative to the centreline of the runway.

The nature of the available visual cues increased the difficulty for the pilot in command to detect the aircraft's increasing displacement from the runway centreline. This included a wet runway surface with a probable lack of surface definition, painted runway markings that were less conspicuous on a wet runway at night, a lack of touchdown zone lighting/centreline lighting on a runway that was wider than normal and the possibility that the HIRL was glaring on the wet windscreen. The investigation concluded that the presence of centreline lighting would have increased significantly the nature of the visual cues available and would have assisted the pilot to recognise the developing sideslip and lateral deviation from the runway centreline.

The lack of a positive flare, a marginal reduction in headwind component and deployment of the right wing's flight spoilers during the final stages of the approach contributed to the high rate of descent at touchdown. The wider runway would have provided an unfamiliar set of cues for judging the flare height. The lack of runway surface definition would have increased the difficulty for the pilot to estimate the height of the aircraft above the runway and possibly had contributed to the lack of a positive landing flare. This was also coupled with a different flap setting from that routinely used during landing.

The aircraft was sideslipping to the right at the point of touchdown. The excursion from the runway was not preventable due to the sideslip and the proximity of the aircraft to the edge of the runway. There was no evidence to indicate that standing water, or adhesion of tyres on the wet runway surface, were factors in the excursion from the runway.

During the final stages of the approach, the copilot was monitoring various parameters. He did not detect the increasing displacement of the localiser, or make any call for correction prior to touchdown. The size of indicated deviation, together with the other instruments being monitored, made this an unlikely deviation to detect.

The investigation concluded that the presence of runway centreline lighting would have increased the visual cues available to the pilot and assisted with his recognition of the developing sideslip and lateral deviation from the centreline.

 
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