What happened
During a night approach to Bankstown Airport, the pilot established visual contact with Air Traffic Control (ATC) while at 2,000 ft. Following a clearance to join the final runway 11 centre, the pilot began a descent. Although the clearance did not mandate a specific altitude, the pilot descended to 1,000 ft, which was 800 ft below the required lowest safe altitude (LSALT) of 1,870 ft. This specific altitude requirement was in place due to two nearby towers reaching heights of 870 ft located approximately 2.5 NM from the aircraft's path.
The investigation
The investigation examined the pilot's decision-making and the environmental conditions during the approach. The pilot maintained that the approach was flown as planned because the obstacles remained visible. While weather camera imagery confirmed that visibility was consistent with the pilot's report, investigators noted that the camera's perspective likely provided a brighter view of the terrain than what the pilot experienced from the cockpit.
Furthermore, the investigation found that the pilot had incorrectly recorded the time for sunset, using data for Young rather than Bankstown. This error led to a perception that there was more usable light remaining than there actually was. The ATSB determined that the flight path used was appropriate for daytime operations but was unsafe for the actual night conditions.
Findings
- The pilot's descent below the LSALT reduced the safety margin regarding separation from terrain and ground-based obstacles.
- An error in calculating the time of last light, caused by using incorrect geographical data, likely influenced the decision to proceed with a visual approach.
- The pilot identified that an instrument approach procedure would have been a more appropriate option for arriving at the airport during the transition from day to night.