Glider pilots have been told to register their flights after a near miss with two F-15 fighter jets.
The British Gliding Association has now advised its members to issue special notices to other aviators when flying in large groups such as competitions.
It comes after a pair of the US Air Force planes, flying at 380mph, came within a split second of smashing into a glider, a report has revealed.
One of the US pilots estimated that the glider had flown just 100ft beneath them and just 330ft ahead.
The military aircraft was traveling information to RAF Lakenheath in Suffolk when the lead pilot saw a glider making a turn in front of them.
The F-15 jets leveled off to avoid the Duo Discus but the pilot rated the risk of collision was “high”.
The UK Air Proximity Board (UKAB) revealed the incident happened on August 14 last year as the fighters were coming in to land at their base in RAF Lakenheath, Suffolk.
The jets were flying at 3,200ft at the time over woodland to the west of Thetford, Norfolk.
The UKAB, which investigates near misses, said the pilots had been warned of the presence of “multiple gliders” by air traffic controllers.
The glider pilot who was taking part in the competition said he had been rising on a thermal when he noticed the jets just over a mile away.
He decided to continue circling to be conspicuous to make sure that the jet pilots saw him and maintained that the collision risk was low.
The report heard that the glider was not visible on the radar system used by RAF Lakenheath controllers.
The United States Air Force criticized the glider pilot, saying:
“The wisdom of operating just to the south of the extended centreline of the main instrument runway of one of the busiest fighter bases in the UK must be questioned.”
UKAB members rated it as a Category B incident, where “safety had been much reduced below the norm”.
The report also questioned how the glider pilot assessed the collision risk as low, saying it had “caused some members to wonder whether he had a particularly robust approach to the risks of fast- jets flying so close by.”
UKAB noted that the gliding competition organizers had not put out an official ‘Notice to Airmen’, known to aviators as a NOTAM warning, about unusual air activity, because they believed it was unnecessary due to all of the pilots being local.