The flight was Delta 118 from New York's John F. Kennedy International Airport.
Delta spokesman Anthony Black told The Atlanta Journal-Constitution the plane was flying in for arrival at Copenhagen Airport on the morning of Nov. 20 when a hydraulic access panel came off.
Black said the hydraulic access panel is a small door on the underside of the aircraft to access avionics and equipment in the wing.
The seven crew members and 161 passengers on the Boeing 757 were not aware of what happened, and the plane landed normally at the airport.
It taxied to the gate under its own power.
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