B738, en-route, south south west of Brisbane Australia, 2013

B738, en-route, south south west of Brisbane Australia, 2013

Summary

On 25 February 2013, a Boeing 737-800 about to commence descent from FL390 began to climb. By the time the crew recognised the cause and began to correct the deviation - their unintended selection of a inappropriate mode - the cleared level had been exceeded by 900 feet. During the recovery, a deviation from track occurred because the crew believed the autopilot had been re-engaged when it had not. The Investigation noted the failure to detect either error until flight path deviation occurred and attributed this to non-compliance with various operator procedures related to checking and confirmation of crew actions.

Description

On 25 February 2013, a Boeing 737-800 (VH-VYE) being operated by Qantas Airways on a scheduled domestic passenger flight from Canberra to Brisbane at night was in the cruise at FL 390 when the aircraft unexpectedly began to climb. The autopilot was disconnected and a descent back to the cleared level was commenced but after the crew subsequently believed that the autopilot had been re-engaged when it had not, the aircraft rolled left and also deviated from track. Control was subsequently regained and the remainder of the flight was uneventful.

Investigation

The Australian Transport Safety Board (ATSB) investigated the event making use of successfully downloaded recorded flight data. Both members of the flight crew had significant experience on the Boeing 737 type - in the case of the Captain, nearly 15,000 of his 17,770 total flying hours and in the case of the First Officer, 6670 of his total 10,230 flying hours. The Captain was PF for the incident sector but at the time of the deviation from clearance was taking a meal break and had handed control of the aircraft to the First Officer.

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