Two RAF jets scrambled to intercept a Latvian cargo plane created a sonic boom over Kent.
The Antonov aircraft lost contact with air traffic controllers and was escorted to Stansted Airport by the pair of Typhoons.
Kent Police received several calls reporting a loud bang coming from the Dartford area at about 16:40 GMT.
An airport spokesman said police officers surrounded the aircraft after it landed at 17:15.
A blast was felt across the county, according to posts on Twitter.
The airport spokesman said surrounding the plane was standard procedure when communication had been lost with an aircraft.
He said officers were later stood down and the plane was continuing its journey.
An RAF spokesman said: "Typhoon aircraft were launched this afternoon from RAF Coningsby to intercept a civilian aircraft south of London which was causing concern to air traffic control authorities.
"The aircraft was safely escorted to London Stansted.
"To fulfil their quick reaction role the Typhoons were cleared to travel at supersonic speed, any noise disturbance as a result of this is regretted."
The RAF confirmed the aircraft was an Antonov An-26.
It apologised if crews had "startled people" but added that jets only went supersonic over land when absolutely necessary.
Essex Police said three people on board, who were all Lithuanian, had been spoken to and it was established everything was in order.
The reason for the short loss of communication was a change in airspace jurisdiction, police said.
Officers said they were not investigating the incident.
Stansted said the plane was expected to leave the airport later but staff still had to organise a take-off slot and refuelling.
A spokeswoman for RAF-AVIA, the Latvian airline that operated the aircraft, said it had been on a routine flight to Birmingham from Italy when the pilots lost communication with air traffic control on entering UK airspace.
She said the technical reason behind the communication failure was still unclear and the company had not yet spoken to its crew.
The plane was carrying equipment for an automotive assembly line.