A helicopter carrying Princess Margaret came within 900 feet of a British Airways jumbo jet as the plane took off from London's Heathrow airport, officials said Friday.

Britain's Civil Aviation Authority (CAA) said it was investigating the incident, which occurred Wednesday.The helicopter was carrying the princess, Queen Elizabeth's sister, from her home at London's Kensington Palace on a journey to Quedgeley, west of London.

The Boeing 747 with 337 people on board bound for Anchorage and Tokyo took off in the opposite direction, then turned north on to the same heading as the helicopter before overtaking and passing above it, a CAA spokesman said.

He said the incident was not reported as a near miss, but an air traffic controller immediately notified the authority that he believed the aircraft might have been as close as 300 feet.