What happened
At approximately 21:33, an aircraft was descending toward Melbourne Airport to perform a nighttime ILS approach to runway 27. The aircraft intercepted the ILS localiser track at an angle of roughly 36°, having already crossed the track before the intercept began. Due to a southerly wind acting on the westbound flight, the aircraft drifted rapidly to the right of the localiser track.
While deviations within the full-scale CDI deflection can be managed via a visual approach with ATC authorization, no such request or authorization was made in this instance. Consequently, the pilot was required to adhere to standard ILS tracking tolerances. The pilot reported that they believed the CDI had not exceeded full-scale deflection and proceeded with the approach visually. However, the aircraft drifted significantly beyond the allowable tracking tolerance, reaching altitudes as low as 980 ft AMSL, which was 2,320 ft below the minimum sector altitude.
The investigation
The investigation focused on the aircraft's failure to maintain the prescribed navigational path during the night approach. It was determined that because the approach was conducted in darkness, the pilot's ability to visually identify potential obstacles was severely restricted. By continuing the approach outside of the localiser tolerance and below the minimum sector altitude, the flight lost the assurance of obstacle clearance, thereby increasing the risk of a collision.
Findings
- The aircraft was not maintained within the necessary navigational tolerances during the approach.
- The approach was continued despite the aircraft maneuvering significantly below the minimum safe altitude.
- The lack of adherence to tracking requirements during a night approach removed essential protections against terrain or obstacle impact.