The Air Accident Investigation Branch is looking into what caused two vintage planes to collide in the air at Duxford over the weekend.
It happened during the Battle of Britain display on Saturday when a pair of American Mustang fighter bombers collided.
One peeled away and made an emergency landing a short while later. Organisers of the show say 19,000 people were watching the airshow at the time.
They say one pilot called a mayday and both planes came in to land.
Fire and Rescue teams immediately went to the scene but both pilots were safe and unharmed.
They say there was no danger to any spectators as they are kept well back from the display area.
You can watch Victoria Lampard's report on what happened by clicking below.
Investigators say they're trying to find out what went wrong.