Examination of a Swiss Airbus A220-300 engine following a fatal smoke and diversion event over Austria has revealed damage to the fan drive gear system as well as bearings.
But investigators probing the occurrence, on 23 December last year, have yet to draw specific conclusions over the circumstanes and the reasons why one of the three cabin crew succumbed after being hospitalised.
Pilots of the aircraft, bound for Zurich from Bucharest on 23 December last year, were alerted to problems with the left-hand Pratt & Whitney PW1500G engine during cruise at 40,000ft.
Smoke entered the passenger cabin and cockpit. Both pilots donned oxygen masks while the cabin crew put on smoke hoods. The crew shut down the engine and diverted to Graz, where the aircraft landed and was subsequently evacuated.
Several of the 74 passengers and all the crew members were taken to hospital for medical treatment. One of the cabin crew members succumbed to their condition six days later, on 30 December.
The affected engine was initially delivered as a spare powerplant to the carrier, before being installed on the aircraft (HB-JCD) in July 2024, less than six months before the occurrence.
Servicing records confirm that all scheduled maintenance was performed in accordance with applicable procedures and timelines, says Austrian federal investigation authority SUB-Zivilluftfahrt, and work from all mandatory airworthiness directives had been completed.
Following a borescope inspection by the engine manufacturer and Swiss technical personnel, the powerplant was transferred from Graz to the USA for analysis.
Damage was found in the fan drive gear system – which connects the low-pressure compressor to the fan – as well as the number 2 and number 4 bearings.
The inquiry says the crew initially received left-hand engine fault messages, with ‘oil debris above limit’ alerts, as well as a vibration warning around the same time as the cabin crew recalled hearing a “loud bang”.
Less than 30s after the vibration warning the pilots detected smoke and immediately put on oxygen masks, just before receiving several smoke alerts. The crew declared an emergency and initiated a descent, notifying air traffic control of the decision to divert to Graz and shutting down the left engine.
After the jet landed at Graz, the captain ordered the cabin crew to prepare for a possible evacuation. The crew then shut down the right-hand engine, and the captain initiated an evacuation about 20s later.
Four of the six exits were used during the evacuation. Neither the forward right-hand nor the aft right-hand exits were opened, although the right-hand overwing exit was. The inquiry has yet to give an explanation, stating: “Investigation into the unused doors is ongoing.”
Two flight attendants had been seated near the pair of forward exits, one assigned to each door, while the third attendant was assigned to both aft exits.
As part of the inquiry the investigators are examining the personal breathing equipment used by the cabin crew, which comprises a hood that encloses the head and seals around the neck. It features a chemical air regeneration system based on potassium superoxide.
“The [breathing systems] have a limited life and are dependent on their correct use,” the inquiry says, adding that cabin crew receive initial and recurrent training on the equipment.
Three of the four units on the aircraft were worn by cabin crew, and all four have been collected for examination in collaboration with the manufacturer. This examination, yet to be completed, includes visual inspection of the hood, and both destructive and non-destructive inspection of special parts.
“Within the investigation, the use of the [equipment] will be evaluated,” the inquiry adds. “This will also include how crews are trained on [its] correct use and how to identify any malfunction with the [equipment].”
