Regulators have mandated temporary operational limitations for Airbus A220 operators in the wake of three Pratt & Whitney PW1500G engine failures in the last three months.
The restrictions, issued by Transport Canada (TC) in an October 25 emergency airworthiness directive (AD), limit engine N1 settings to 94% while operating above 29,000 ft (FL290). The European Aviation Safety Agency adopted the directive, and others are expected to follow.
"Several occurrences of engine in-flight shutdowns (IFSDs) were reported” on A220s, TC’s directive said. "Investigations are ongoing to determine the root cause. Preliminary investigation results indicate high altitude climbs at higher thrust settings for engines with certain thrust ratings may be a contributor.”
The AD "introduces a new aircraft flight manual limitation and normal procedure to limit the engine N1 setting to 94% while above 29,000 feet,” the directive said. Any instance of exceeding 94% for “more than 20 continuous seconds” must be reported, it added.
Meanwhile, the U.S. National Transportation Safety Board continues to probe failures of three Swiss International PW1524G-3s. The first two, on July 25 and September 16, involved low pressure compressor (LPC) stage 1 rotor failures, investigators confirmed. Details on the third, which occurred Oct. 15, have not been released.
All three failures occurred on Swiss's London Heathrow-Geneva route, and led to diversions. The first and third incidents ended with diversions to Paris Charles de Gaulle, while the second flight returned to Geneva. No injuries were reported. NTSB was designated as lead investigative agency for all three incidents.
Following the second incident, Pratt recommended inspections of LPC stage 1 rotors and inlet guide vanes, and regulators quickly mandated the instructions. The checks applied only to engines with fewer than 300 cycles.
Swiss grounded its fleet of 28 A220s for precautionary engine inspections following the third incident and returned them to service within a day. Swiss operates 20 A220-300s and eight -100s. As of Sept. 30, Airbus delivered a total of 56 -300s and 34 -100s to airlines. Swiss has the most A220s in service.