Incident
On 19 September 2013, at 2130 UTC, a BAe 146-300 aircraft, registration EC-LOF, was operating a cargo flight from Exeter Airport to Liege Airport with two pilots on board. During the climb, as the aircraft passed FL220, the FREIGHT DOOR UNLOCKED warning light illuminated on the Master Warning Panel. The crew completed the appropriate abnormal procedure.
Shortly after, the pilots heard loud, intermittent and unidentified noises emanating from the main cargo area. Although there were no additional abnormal indications, the combination of the warning and the noise led the pilots to suspect that the aircraft may have suffered structural damage. They declared an emergency to ATC and requested a diversion to the nearest suitable airport. ATC instructed the aircraft to divert to London Gatwick Airport, where it landed without further incident. Throughout the incident, the pressurisation system performed normally, although the unidentified noises continued until after landing.
Engineering Investigation
An engineering investigation found two unrelated faults. The FREIGHT DOOR UNLOCKED warning was caused by a freight door latch proximity switch being out of adjustment. The noises were probably caused by a flexible duct in the air conditioning bay becoming detached. This duct normally connects the right air-conditioning pack to a non-return valve (NRV) on the pressure bulkhead; NRV cycling or the pipe moving around in the bay may have caused the noises. There was no indication that the two faults were connected.
Conclusion
The pilots were faced with two unrelated faults in succession. The freight door warning, coupled with the subsequent loud noises, led them to believe that the indications were connected and that the aircraft had suffered structural damage. The crew carried out a successful diversion to London Gatwick Airport. There were no injuries to the two crew members, and no damage to the aircraft.