What happened
On 16 October 2017, a Jetstream 41, registration G-MAJC, was conducting a commercial passenger flight when the flight crew noticed a burning smell through the cockpit air vents while descending through FL150. The crew immediately donned oxygen masks and declared a MAYDAY, initiating an expedited approach to Hawarden Airport.
During the descent, the crew encountered significant communication difficulties. The use of oxygen masks, combined with the selection of the interphone, created high noise levels and feedback whistles, making it difficult for the commander to communicate with the cabin crew. Upon landing on Runway 22, the commander taxied the aircraft to a stop on Taxiway ‘D’. Due to the uncertainty regarding the conditions inside the cabin, the commander ordered an emergency evacuation.
During the evacuation, the aircraft's engines continued to run at idle for several seconds, and the propellers remained in motion for approximately 40 seconds after the engines began to run down. As passengers exited, the right overwing emergency exit door was blown forward by the wind into the rotating right propeller. Additionally, the aft service door was struck by the propeller wash. The evacuation resulted in one minor injury to a passenger, while the crew remained uninjured.
The investigation
The AAIB investigation established that the burning smell was not caused by a mechanical failure within the aircraft, but was instead the result of smoke and dust from North African and Iberian forest fires carried into UK airspace by atmospheric currents.
Investigators examined the aircraft's communication systems and found that selecting the oxygen mask microphone on the Audio Control Panel activated the cockpit speakers in a way that could not be turned off, leading to the intense breathing noise. The investigation also reviewed the engine shutdown sequence, noting that the propellers continued to rotate significantly after the commander had initiated the evacuation and shut down the engines.
Findings
- The primary cause of the smoke in the cockpit was atmospheric smoke and dust from external forest fires and desert dust.
- The crew's communication was severely hindered by high noise levels and feedback caused by the use of oxygen masks and specific audio panel settings.
- The emergency evacuation was conducted in a rushed manner due to high stress and a lack of information regarding the cabin state.
- The engines and propellers remained in motion for a period after the shutdown command, creating a hazard during the exit of passengers.