Airbus A220 'Whisperjet' is too loud, according to Zurich residents

Airline Swiss greeted the arrival of its latest plane with great fanfare, dubbing the Airbus A220 model the "Whisperjet" and promising neighbourhoods around Zurich Airport that it would be 50 per cent quieter than older aircraft.

But that tag has come back to haunt the Lufthansa unit as the narrow-body's twin engines emit what locals have described as a strange howling noise as it comes in to land, enraging people living on the flight path.

"It's even louder than other machines flying in," said Klaus Stoehlker, spokesman for the Zurich-based Foundation Against Aircraft Noise. "They've been describing it as temporary while they make assessments, but for nine months now it hasn't gone away."

Zurich Airport has received complaints on its noise hotline of unusual sounds when the A220 passes overhead, a spokeswoman said, adding that it's working with Swiss to seek a quick solution. The plane -- developed by Bombardier and now part of the Airbus lineup -- isn't breaching rules and the sound, which last for a few seconds, hasn't triggered higher fees that apply to louder jets.

Airbus and Swiss each said they are aware of the situation and in close contact with engine maker Pratt & Whitney, which is analysing the noise -- likened by some to the mating call of an orca whale -- to determine its cause. The sound "occasionally occurs" during throttle movements when A220 is at low power, a Pratt spokeswoman said, adding that the jet's total noise footprint still represents a 75 per cent improvement on older planes.

The issue, which affects A220 models seemingly at random, risks blemishing the plane's credentials as ideal for noise-limited airports. Hubs including Frankfurt operate strict night curfews, while London City, which Swiss also serves with the plane, restricts weekend flights.

The Whisperjet name has been applied to a variety of planes over the decades, including the BAE-146 and Eastern Airlines Boeing 727s, whose tail-mounted engines made the front of the cabin quiet but the rear especially noisy.

Airbus and Bombardier first announced their tie-up last October as Canadian jetmaker Bombardier looked for a resolution to a trade dispute in which the United States threatened tariffs of up to 300 per cent on the CSeries jets. The threatened tariffs followed a formal complaint launched by Boeing that alleged unfair subsidies for the Canadian-made jet, which was buoyed by a large order from Atlanta-based Delta.