What aircraft was involved and where did it happen?

The accident on 2003-03-02 involved a BAE 146-300, registration G-OINV, at In the cruise, near Carlisle, Cumbria, GB.

What was the probable cause of the accident?

The primary cause of the control restriction was insulation material becoming entangled in the aileron cables, while the failure to resolve the restriction was due to an unclear checklist that did not adequately instruct the crew to apply a breakout force to the control column.

Aileron control restriction on BAe 146-300 during cruise

A flight of a BAe 146-300 experienced restricted lateral flight controls near Carlisle due to loose insulation material interfering with the aileron control cables.

What happened

On 2 March 2003, a BAe 146-300, registration G-OINV, was performing a scheduled public transport flight from Inverness to London Gatwick. While cruising at FL250 near Carlisle, the aircraft was instructed by ATC to execute a right turn. Although the autopilot initially attempted the maneuver, the aircraft failed to achieve the required heading, maintaining only a minimal bank angle. An "AIL" warning illuminated on the Master Warning Panel.

Upon disconnecting the autopilot to fly manually, the commander discovered significant restrictions in the lateral flight controls, noting that the control wheel felt extremely heavy and the maximum achievable bank angle was limited to between 10 and 15 degrees. The crew performed the required memory items and consulted the 'AILERON JAM OR UNCOMMANDED ROLL' checklist. After consulting with the company operations department, the crew decided to divert to Manchester Airport. During the descent, the crew noted that the control forces gradually returned to normal, and the aircraft landed without further incident. There were no fatalities and no injuries among the 5 crew members and 95 passengers.

The investigation

The AAIB investigation focused on the cause of the control restriction and the crew's response to the emergency. Engineering inspections at the operator's maintenance facility revealed that sections of insulation on the rear wing spar had become dislodged from their retaining buttons. This loose insulation had become entwined with the aileron control cables as they passed through pressure bungs on both the left and right sides of the aircraft.

Investigators also examined the effectiveness of the crew's emergency procedures. While the crew correctly initiated the memory items, they did not apply the necessary breakout force to the control column required to fully achieve the aileron circuit disconnection. The investigation noted that the crew did not believe the specific note regarding the need for immediate response was applicable to their situation.

Findings

The lateral flight control restriction was caused by loose insulation material becoming trapped in the aileron control circuit.
The insulation bags had become dislodged from their retaining buttons on the rear wing spar.
The crew failed to complete the full disconnection procedure because the checklist did not sufficiently clarify that a breakout force must be applied to the control column.
A previous safety recommendation regarding the clarity of these manuals had been addressed by the manufacturer, yet the ambiguity persisted.

Safety action

Safety Recommendation 2004-13: The AAIB recommended that the Civil Aviation Authority ensure BAE Systems revises the Manufacturer's Operating Manuals for the Avro RJ and BAe 146 to clarify the operation and procedures associated with the aileron disconnect systems.