Carriers using Airbus A220s are being advised to monitor the operating performance of low-pressure compressors, to warn of stalls, following measures to address engine failures on the type.
A220s are fitted with Pratt & Whitney PW1500G powerplants, which have been the subject of scrutiny following a series of engine failures involving Swiss and Air Baltic aircraft.
Analysis has indicated that the low-pressure compressor’s stage-one rotor was vulnerable to acoustic resonance, after a change to the vane schedule from a full-authority digital engine control software update.
Operators have been instructed to revert to a previous vane schedule with revised software.
But the US FAA says this can result in a lower stall margin for the compressor, resulting in deteriorated or dirty engines experiencing recoverable stalls at the top of climb.
In a special bulletin, the FAA says two such stalls have occurred on the same PW1500G powerplant.
While it says this concern does not warrant an airworthiness directive, it is recommending that A220 operators “continuously monitor” the operating performance of the low-pressure compressor.
Pratt and Whitney has a method to monitor this performance, the FAA adds, which uses engine data provided by carriers, enabling the detection of deteriorated compressors before the onset of stalls.