A probe into a series of failures with Airbus’s smallest jet, the A220, is trying to determine whether a software change set off unexpected vibrations that damaged fast-moving parts and forced three emergency landings, people familiar with the case said.
Swiss International Air Lines briefly halted its fleet of A220 jets for checks on October 15 after a third flight in as many months was forced to divert because of engine damage.
Engine maker Pratt & Whitney, which manufactures the A220 on behalf of Airbus and which made the engines that had the three emergency landings, also expanded checks on similar engines worldwide.
Investigators are focusing their attention on recent changes in engine software that may have caused parts that compress air inside the engine to be set in a way that caused mechanical resonance or destructive vibrations, two of the sources said.
Neither the aircraft nor the engine has been grounded, but pilots have been told to avoid certain combinations of thrust settings and altitude to avoid the risk of a new problem until the root cause of the three engine failures is found.
A third source said it might take until December to confirm the cause, while other scenarios have also not been ruled out.
Airbus, which is based in the Netherlands and was starting a Pacific tour to promote the A220 on Thursday, had no immediate comment on the investigation.
Officials at the United States National Transportation Safety Board, which is leading an investigation into the recent failures involving the engine, declined to comment.
The European Union Aviation Safety Agency said it was monitoring the situation closely and coordinating with the US Federal Aviation Administration.
The head of Pratt & Whitney parent United Technologies said earlier this week that it was working on finding the cause and remained confident in the new fuel-saving engine.
“Clearly, any time you get an issue like this, we’re on top of it. The guys are working through it,” United Technologies Chief Executive Greg Hayes told analysts on a conference call.
No one was hurt in the three incidents, which all took place during flights over France between London and Geneva. But parts from two of the A220 engines were found on the ground.
France’s air-accident agency – the Bureau of Enquiry and Analysis for Civil Aviation Safety – has launched a rare appeal for 150 volunteers to help search a wooded area in eastern France for a key component of the engines during the coming weeks.
Pratt & Whitney set off a chain reaction of new aircraft designs or upgrades in 2008, when it announced its new geared turbofan engine, promising 16 percent fuel savings. But since then, it has wrestled with a spate of performance or reliability problems and delays.
Although software problems can take time to fix, experts say they are more likely rectified with a software update rather than by designing a new part.
Formerly known as the CSeries, the 110-130-seat A220 was designed by Canada’s Bombardier Inc and was one of the first to adopt the new Pratt & Whitney technology. Bombardier sold the programme to Airbus last year due to heavy losses.
The Airbus version of the engines is not affected by the recent problems and is not subject to checks.
Some competing Brazilian aircrafts such as the Embraer 190 and 195-E2 have also been subject to such engine checks, but reportedly use a different version of the software from the larger A220.