Back in February 2020, a Titan Airways A321 aircraft was involved in a serious incident upon departure from London Gatwick. Due to an engine stall, pilots had to declare MAYDAY and make an emergency landing. On March 4, 2021, the UK’s Air Accidents Investigation Branch (AAIB) issued the final report, explaining what happened on that day.
MAYDAY over London Gatwick
On February 26, 2020, an Airbus A321, registered as G-POWN, took off from London Gatwick Airport (LGW), the United Kingdom.
When the aircraft was at around 500 feet, its left engine began to surge and caught fire. Declaring MAYDAY, the pilots decided to turn back to the airport. However, before they could make the landing, the flight crew received another indication ‒ this time the right engine had stalled.
Having decided that the engines were more stable at low thrust settings and the thrust available at those settings was sufficient to maintain a safe flight path, as investigators found out, the pilots continued the approach and landed the aircraft back in London Gatwick approximately 11 minutes after the takeoff.
Engine problems on four flights within 24 hours
When investigating the serious incident, AAIB found that both engines were operating abnormally on four flights ‒ all within the 24 hours preceding the incident over Gatwick.
During one of the previous incidents, pilots even reported momentary indications of the right engine stall. But when the aircraft was inspected, no fault was found. However, the AAAIB now found that the inspection itself was flawed as it was carried out using an inappropriate procedure: while the procedure had been indeed outlined in an aircraft troubleshooting manual, it was not applicable to this particular aircraft.
So what went wrong with the A321 engines?
The A321 engine trouble started after the aircraft returned from a scheduled maintenance two days prior to the MAYDAY flight, on February 24, 2020. The maintenance had been carried out overseas and involved a biocide shock treatment on the fuel system. To treat microbial contamination, the maintenance providers used Kathon biocide.
It was the Kathon biocide treatment that was responsible for two out of three causal factors that the AAIB investigators established. The investigators found that the aircraft fuel tanks were treated with excessive Kathon concentration levels ‒ in fact, around 38 times over the recommended norm ‒ which caused contamination of the engine Hydro Mechanical Units (HMU). This caused the loss of correct HMU regulation of the aircraft’s engines.
The third factor, in addition to excessive Kathon concentration and damage to HMU, relates to the abovementioned engine stall inspection. The investigators found that to inspect the right engine, the maintenance crew used a troubleshooting procedure that applied to LEAP-1A32 engines. The only trouble is, the aircraft in question was fitted with CFM56 5B3/3 engines.
“The procedure for CFM56-5B3/3 engines required additional steps that would have precluded G-POWN’s departure on the incident flight,” is outlined in the report.
The aircraft involved in the incident, the Airbus A321-211 registered as G-POWN, is a 12-year-old aircraft belonging to Titan Airways. Following the incident, it was stored at LGW until June 30, 2020. Since then, it has been returned to active service, Radarbox.com data indicates.