An Air India Boeing 777 flying from Mumbai to Newark, New Jersey, landed safely after being diverted.
Essex police said Thursday there had been a security alert.
The flight, which was diverted Thursday at 10:15 a.m. BST (0915 GMT), was parked on an isolated stand far from the airport's normal operations.
The plane was later cleared and took back off for the United States.
The U.K.'s Ministry of Defense did not identify the plane involved but did say that Typhoon aircraft safely escorted a civilian aircraft to the airport, which lies around 37 miles northeast of the center of London.