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Final Report

Summary

On 12 February 2017, a Boeing 747-47UF (freighter) aircraft, registered N416MC, operating from Honolulu, Hawaii, conducted an approach to Sydney Airport, New South Wales. On board the aircraft were two flight crew. The captain was the pilot monitoring and the first officer was the pilot flying.  

Shortly after the turn onto the final approach for the runway 16R instrument landing system approach, the first officer called ‘glideslope captured’ and the aircraft started to descend with the autopilot engaged. However, the captain’s primary flight display indicated the aircraft was below the glideslope. As the aircraft descended through 2,100 ft, the approach controller requested confirmation that they were established on the glideslope. The captain responded that they had an interruption on glideslope and would maintain altitude until they could re-intercept. During the response, a minimum safe altitude warning alert appeared on the approach controller’s radar for N416MC. The controller immediately issued a go-around instruction and the captain immediately acknowledged the instruction and conducted a missed approach. A second approach was flown with the autopilot engaged and no anomalies were detected.

This incident highlights the importance of crosschecks on the flight deck and between air traffic control and the flight crew. After detecting unexpected indications on the flight deck, the flight crew intervened to stop the descent, which was then followed by an instruction from air traffic control to initiate a go-around.

The aircraft manufacturer and regulators have recommended that flight crew remain vigilant for instrument landing system disturbances with resulting unexpected flight control movements and be prepared to immediately disconnect the autopilot, particularly during autoland operations.

Aviation Short Investigations Bulletin Issue 61

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