Dozens of planes were diverted or delayed as Heathrow was forced to suspend arrivals due to a Royal Air Force flight, according to the airport.
A spokesman for the west London hub said the RAF's request for airspace closure was "unplanned".
The closure of airspace - which began at around 9am this morning - lasted for approximately 20 minutes.
At least four Heathrow-bound British Airways flights and one Virgin Atlantic aircraft were forced to land at other airports such as Gatwick, Stansted and Luton.
A spokesman for Heathrow said arrivals were paused briefly this morning due to an RAF request for an operational flight within part of Heathrow's airspace.
An RAF spokesman was not immediately able to identify an operation near Heathrow.