What happened
On 16 October 2006, a Boeing 737-800, registration TC-JGR, departed London Stansted Airport for Istanbul Ataturk Airport. Shortly after takeoff, the aircraft entered a steep nose-down attitude and leveled off at approximately 500 ft aal (9/00 ft amsl). The aircraft maintained this low altitude for roughly 6 nautical miles before receiving instructions to climb.
During the flight, an Air Traffic Control (ATC) controller observed the aircraft's unusually low altitude. The crew initially struggled to establish contact with the en-route controller, and the aircraft's altitude was noted as being significantly below the Minimum Safe Altitude (MSA) of 1,800 ft amsl. The aircraft eventually reached its cruising level and completed the flight without further incident, with no fatalities or injuries reported.
The investigation
Investigators examined flight recorder data, which revealed that the autopilot was engaged shortly after takeoff. The system attempted to capture a pre-selected altitude of 900 ft, but due to a 'late acquire' function, the aircraft overshot this altitude, reaching a peak of 1,186 ft before descending back to 900 ft. The commander manually took control to descend to the selected level, which triggered several 'Don't Sink' and 'Sink Rate' alerts from the Enhanced Ground Proximity Warning System (EGPWS).
Analysis of the crew's briefing showed that the co-pilot had briefed the departure based on the 'Dover Five Sierra' SID. The investigation looked into why the crew did not realize the departure profile required a specific initial climb straight ahead to 500 ft aal, which would have prevented the level-off at 900 ft.
Findings
- The crew misunderstood the instructions on the SID plate regarding the initial climb profile.
- A breakdown in Crew Resource Management (CRM) meant the commander's initial doubts regarding the altitude were not addressed through clarification with ATC.
- The incorrect selection of 900 ft in the altitude pre-selector led to the aircraft leveling off prematurely.
- The incident was made less dangerous by the fact that the aircraft was operating in Visual Meteorological Conditions (VMC) and the terrain was not extreme.