What happened
On 9 October 2022, an ATR 72-212 A, registration G-CMFI, arrived at Leeds Bradford Airport on a commercial passenger charter from Biggin Hill. While the aircraft was decelerating below 70 knots on the runway, the crew received a master caution alert for an electrical inverter fault, immediately followed by a master warning for electrical smoke.
The flight crew detected the smell of smoke on the flight deck. Although the senior cabin crew initially reported no smell in the passenger cabin, a subsequent check of the cabin confirmed the presence of smoke. While no visible smoke was seen externally and no hotspots were detected by the fire service, the commander decided to perform a rapid disembarkation on the runway to avoid the need for a full emergency evacuation.
To maintain cabin lighting during the dark conditions, the commander elected to keep the right engine running in 'Hotel mode'. The passengers and cabin crew exited the aircraft via normal exits and were transported to the airport, while the pilots remained on board to manage the aircraft's towing. There were no injuries to the 41 passengers or 4 crew members, and no damage was sustained by the aircraft.
The investigation
The investigation focused on the source of the smoke and the procedures used during the disembarkation. Investigators identified that the smoke originated from the failure of static inverter 1.
Regarding the disembarkation, the AAIB examined the operator's manual and the crew's actions. It was noted that the commander did not use the passenger address system to inform passengers of the situation, and the standard evacuation checklist was not followed. Furthermore, the investigation looked into the lack of specific procedures for conducting a rapid disembarkation while engines are still operating.
Findings
- The source of the smoke was a failure of the number 1 static inverter.
- A vendor service bulletin existed which recommended replacing capacitors in certain inverters to prevent high failure rates, but the operator was unaware of this specific information.
- The operator's maintenance department had not been treating manufacturer Airworthiness Operator Messages (AOMs) with the same level of scrutiny as mandatory service bulletins.
- There was no established procedure for a rapid disembarkation while engines were running, leading to the use of 'Hotel mode' without an explicit assessment of the associated risks.
Safety action
- The operator has replaced the affected inverter with a different model.
- The operator has updated maintenance procedures to ensure all manufacturer AOMs are reviewed and treated with the same importance as safety bulletins.
- New guidance and checklists are being developed to clarify the distinction between a full evacuation and a precautionary rapid disembarkation.