SEATTLE (AP) _ Two jetliners were forced to return to the airport Tuesday after they developed problems shortly after takeoff.

Engine trouble forced American Airlines Flight 526 headed for Chicago to turn back and make an emergency landing early Tuesday at Seattle-Tacoma International Airport, the airline said.

Tuesday afternoon, United Airlines Flight 875 bound for Tokyo also turned around and landed at the airport after the crew reported an odor.

Both planes landed safely in the unrelated incidents.

The American Airlines flight turned around soon after the compressor in one of the MD-80's two engines stalled, said Tim Wagner, a spokesman for Fort Worth-based American.

Passengers were placed on another plane.

The cause of the odor aboard the United plane _ a Boeing 777 _ had not been determined, airline spokeswoman Megan McCarthy said from Chicago.

One flight attendant was checked by paramedics for respiratory discomfort, but there were no other reports of injuries, McCarthy said.

The plane was taken out of service, and passengers were to be put on a replacement plane for the flight Wednesday morning.

Elsewhere Tuesday, American Airlines Flight 1107 _ departing Tampa for Dallas _ immediately returned to the airport when its nose gear doors failed to close.

The pilot reported a strange vibration and asked to return to Tampa. Afterward, the MD-80 aircraft was taken out of service for repairs, Wagner said.