Alaska Airlines jet engine cover rips off during emergency landing

It started with an "unusual vibration" on the left side of a busy US commercial jet and ended with the plane's engine cover ripping right off during an emergency landing.

The Alaska Airlines flight from Seattle to San Diego, carrying 176 passengers and six crew, was forced to turn back yesterday because its engine cowling had broken free.

Dramatic video posted to social media, purportedly of the plane, showed a large piece of cowling flapping wildly during the flight and then completely tearing off on landing.

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Other photos posted to Twitter showed the plane's damaged and exposed engine, when it was finally parked on the tarmac.

"Crazy, crazy. I was on this flight," wrote Jacqueline Stonas.

In a statement, Alaska Airlines said crew onboard Flight 558 had reported an "unusual vibration" on the aircraft shortly after take-off.

The jet returned to Seattle-Tacoma International Airport and landed safely, but "part of the metal paneling that covers the engine, called the cowling, detached from the aircraft when it landed," the airline said.

The Boeing 737-900ER has been grounded while engineers investigate the incident.

The pilots and flight attendants handled the incident and landing with "tremendous professionalism and care," the airline said.

"We also greatly appreciated the patience of our guests during this event."

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