Library image of a USAF F-15 (Picture: US Department of Defense).
Two US fighter jets flying at 350 miles per hour avoided a collision with a pair of parachutists in Cambridgeshire, a report has found.
The skydivers, who were freefalling at around 120 mph, recorded the F-15 fighter jets pass below them on a helmet camera.
The UK Airprox Board, who produced the report, said they could "clearly see" the jets fly below the skydivers in the footage.
It said it could not establish how close a collision was due to a "lack of information".
The incident on 17 April was placed in the second-highest danger category, with the reported concluding "safety had been reduced much below the norm".
The report said: "It was unlikely that the pilots would have been able to see the parachutists and take avoiding action, and in this case they were unaware that they had flown beneath them."
The pilots from RAF Lakenheath in Suffolk said they were not aware parachutists were flying from the Chatteris airfield.
The report said it was "unfortunate" that the pilots had not been informed the airfield was active.
The report added the pilots had not been warned because they had been handed over from air traffic controllers at RAF Coningsby to RAF Lakenheath "at a busy time".
However, the pilots "should have known" about the position and activities at Chatteris airfield "as part of their normal briefing routine", and should have either questioned air traffic control or just avoided it, the board said.
The report said workers at Chatteris airfield call nearby air traffic controllers each morning to say whether they are active and that aircraft also alert them when airborne.
The Airprox report also highlighted there had been an "extended debate" over whether there had been a risk of collision and stated board members had disagreed over how close the risk of collision was.
The Board praised Chatteris' operators for their "pro-active approach" and said "there was very little more that Chatteris could have done".
The US Air Force (USAF) was rebriefing its crews to make them more aware, the report added.
Colonel Will Marshall, 48th Fighter Wing commander, said: "UK airspace is incredibly complex and often congested, and safety is our shared top priority in aviation.
"We are using this incident to reinforce the vital importance of situational awareness and attention to detail for our all of our air traffic controllers and aircrew.”
RAF Lakenheath is home to USAF's 48th Fighter Wing and is currently undergoing a £160 million project to welcome two F-35 Lightning squadrons.