What happened
On 2 March 2021, an Airbus Helicopters AS355 F1, registration G-BOSN, was performing commercial filming operations near Bourne End, Buckinghamshire. While the aircraft was in a 20 ft hover, the aerial coordinator noticed smoke emanating from the engine exhaust. The pilot initiated a precautionary landing, during which the smoke intensified. Just before touchdown, the coordinator reported visible flames. Upon landing, the pilot shut down both engines and activated the fire extinguishing system after a fire warning light illuminated. There were no injuries to the crew or the passenger.
The investigation
Investigators examined the right engine bay and discovered that the inboard exhaust nozzle had become detached. This detached component had lodged within the aircraft-mounted exhaust tube, obstructing the outlet and forcing hot exhaust gases onto the engine cowlings. This resulted in paint blistering, melted cowl latches, and damage to electrical wiring and connectors.
Metallurgical analysis of the V-band clamp revealed a fatigue crack that had propagated across nearly the entire width of the tightening band. The examination also found that the clamp had been fitted with an incorrect serrated locking washer instead of the required tab washer. Furthermore, the engine was found to be operating with elevated vibration levels due to a damaged compressor bearing.