TAMPA, Fla. -- A bird is not to blame for a dent in the nose of a Northwest Airlines plane that landed in Tampa, according to federal officials.

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IMAGES: Images Of Damage

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Federal Aviation Administration spokeswoman Kathleen Bergen said Tuesday that the aircraft's fiberglass nose cone and an antenna were shipped to Minneapolis for analysis.

An FAA spokeswoman in Chicago said officials haven't determined what caused the dent yet, but there is "definitely no evidence of a bird strike."

Bergen said the crew aboard Flight 478 from Detroit reported a loud bang Monday and then the aircraft's radar became inoperative. The aircraft landed safely.

"I don't if they noticed anything was wrong until they got onto the gate and we're walking past the windows and saw the plane the commotion that was happening at the windows," a passenger said.

A Tampa International Airport spokeswoman initially blamed the dent on a bird, but Bergen said the crew reported the bang while flying at 18,000 feet -- an altitude too high for a bird.