What happened
On 7 February 2010, a Boeing 737-33A, registration G-CELC, was performing a commercial passenger flight from Leeds Bradford Airport to Chambery Airport, France. While executing an ILS approach to Runway 18 in instrument meteorological conditions, the flight crew encountered difficulties with their navigation indications.
During the approach, the commander noticed a loss of ILS information on his electronic attitude indicator. In an attempt to resolve the issue, the commander cycled the navigation frequency switch. While his attention was diverted to the instrument panel and a communication from air traffic control, the aircraft began a rapid descent. The co-pilot, acting as the pilot flying, initiated a descent at a rate of approximately 2,200 fpm after observing a movement in the glideslope pointer.
As the aircraft descended, the terrain closure rate increased significantly. At an altitude of 1,125 ft, the EGPWS Mode 2 'Terrain and Pull Up' warning activated. The co-pilot immediately disconnected the autopilot and initiated a manual go-around. During the maneuver, the aircraft reached a maximum nose-up pitch of 32.7°. The aircraft successfully climbed clear of the terrain and returned to the holding pattern, where a second approach was subsequently completed without further incident.
The investigation
Investigators examined the aircraft's flight data recorder and EGPWS computer. The FDR confirmed that the aircraft's descent rate increased to approximately 6,000 fpm at the point of minimum terrain clearance, which remained above 1,100 ft. The investigation also reviewed the serviceability of the airport's navigation aids. A recent flight inspection of the Chambery ILS had found the system to be fully functional, and no subsequent faults were reported.
Findings
- The commander's attention was diverted while attempting to rectify a momentary loss of ILS indications by cycling the AUTO/MAN switch.
- The pilot flying initiated an excessive rate of descent in response to perceived glideslope movement before the descent profile could be cross-checked.
- The EGPWS warning was triggered by a high closure rate with terrain during the descent.
- The commander's focus on the navigation frequency switch and ATC instructions meant he was unaware of the aircraft's vertical profile until the situation was queried.