What aircraft was involved and where did it happen?

The accident on 2002-12-12 involved a BAE.146-200, registration G-JEAX, at Birmingham, GB.

What was the probable cause of the accident?

The accident was caused by the icing of the elevator servo tabs, likely due to precipitation accumulating in the control gaps during ground operations, combined with a crew response to the situation for which they had not been trained.

Pitch Control Malfunction Leads to Injuries on BAe 146

A flight of a BAe 146-200 experienced severe pitch oscillations and heavy control forces during climb, resulting in serious injuries to cabin crew.

What happened

On 12 December 2002, a BAe 146-200, registration G-JEAX, was performing a scheduled passenger flight from Birmingham to Belfast City. During the climb, the flight crew observed unusual, low-frequency pitch oscillations while the autopilot was engaged. As the aircraft approached its assigned flight level of FL240, it failed to level off and instead continued to climb.

Upon disconnecting the autopilot, the commander experienced extremely heavy elevator control forces. The pilot applied nose-down electric trim, which caused the aircraft to pitch down sharply. In an attempt to recover, both pilots applied significant rearward force to the control columns. This sudden movement caused the controls to release abruptly, resulting in a rapid pitch-up and a violent acceleration event. The sudden movement caused two serious injuries to cabin crew members and minor injuries to others.

The investigation

The AAIB investigation focused on the mechanical state of the pitch control system and the environmental conditions prior to departure. Investigators examined the elevator trim and servo tabs, finding traces of de-icing fluid residue in the control gaps. While the residue itself was not thick enough to cause a direct jam, its presence suggested that moisture or precipitation could have accumulated in the gaps.

Further examination of the servo tab rod-end bearings revealed they were completely devoid of grease, containing only a powdery residue. This lack of lubrication increased the stiffness of the control system. The investigation also reviewed the aircraft's history of exposure to snow and rain at Birmingham prior to takeoff, noting that the aircraft had not been de-iced because no visible accumulation was present on the wings or fuselage.

Findings

The primary cause of the pitch instability was the icing of the elevator servo tabs, likely caused by precipitation (snow, rain, or hail) accumulating in the control gaps while the aircraft was parked in near-free and then freezing in flight.

The lack of grease in the servo tab bearings increased the stiffness of the pitch control system, potentially contributing to the severity of the event.

The flight crew's response, while aimed at maintaining the assigned altitude, resulted in high vertical accelerations that caused the injuries.

There was a lack of specific emergency procedures or training to help crews manage the unique challenges of frozen or heavy flight controls on this aircraft type.