A failure to act on performance alerts from the engine manufacturer contributed to the in-flight failure of a CFM International CFM56 powering an Air India Express Boeing 737-800.
The incident occurred on 26 December 2022 after the aircraft, VT-AYC, took off from Tiruchirappalli on an overnight service to Singapore operating as flight IX-682, according to a probe from India’s Directorate General of Civil Aviation.
While passing 23,000ft, the crew heard “a thud sound” followed by indications of a sharp reduction in N1 speed on the No.1 engine, falling from 98% to 65%. Subsequently, the fuel flow on that engine started dropping rapidly and the exhaust gas temperature shot up to 913°C (1,680°F). N2 speed also began to fall.
Although other parameters remained within limits, vibration levels in the low-speed turbine and the fan increased, and the crew idled the engine in accordance with the non-normal checklist.
The aircraft diverted to Chennai and landed safely, with no injuries to the 160 passengers and six crew.
After landing, an inspection revealed damage to the third and fourth stage low-pressure turbine rotors and stators “with missing materials and a lot of broken pieces between the fourth stage stator and rotor.” Damage from foreign object debris was ruled out.
In its analysis, the DGCA says that CFM had issued a customer notification report (CNR) on 20 December – six days before the incident flight – warning of degraded performance to VT-AYC’s No.1 engine.
Work was planned to follow up on the CNR and other aircraft maintenance items, but owing to aircraft movement changes and a lack of ground time available these did not take place. The DGCA, however, believes that there were two periods when the aircraft was on the ground long enough for the work to have been conducted.
In addition, the DGCA found that myCFMPortal – which monitors engine health – showed a series of alerts flagging the engine’s degrading performance before the incident flight, but that these were missed by the carrier’s maintenance team.
“This implies that there is no proper monitoring of the myCFMPortal to analyse the performance degradation by the concerned department,” says the probe.
The DGCA warns that further action may follow.
