An RAF Jaguar jet came within 100m of colliding with two gliders in Powys, it has been revealed.
The Jaguar was on a training exercise from RAF St Athan
An official report has found that the risk of a collision was high, and that a disaster was averted was due more to luck than anything else.
The jet, on a training mission from RAF St Athan in October 2003, was travelling at 490mph (780kmph).
The Civil Aviation Authority's Air Proximity Board (Airprox) recommended briefings for military pilots.
The official report described how the jet was travelling at 500ft near Talgarth when it passed between the craft from the Black Mountains Gliding Club.
The report said the RAF pilot, from St Athan in the Vale of Glamorgan, gave a frank account of what happened.
He said that if he had seen one of the gliders a second later he would have hit its tail.
The pilot took evasive action, pulling the jet into a hard right-hand climbing turn.
Noting other incidents in 2001 and 2002, Airprox recommended improved briefings for military pilots about gliding in the Black Mountains.
Gliders share airspace with military jets, away from commercial air traffic
It also warned that glider pilots have developed a "number of misconceptions" about RAF flying and suggests that new restrictions should be imposed in the area.
Both glider pilots were experienced. One was a local instructor and the other was a regular visitor to the 100-member gliding club from Sussex, who was left "shaking" and "angry" after the experience.
Don Puttock, resident instructor at the Black Mountains Gliding Club, said the main lesson to learn was that RAF pilots should be aware that gliders and paragliders were likely to be found close to ridges and in particular winds, which allow their craft to soar and stay airborne.
"Gliders, microlights and paragliders share the same airspace as military aircraft, we all have the same rights and on occasions the two are in the same area.
"Both use uncontrolled airspace and the area coming under air traffic control is expanding, which is scrunching us up. Jets typically have their own preferred routes and they can, by their nature, be very hard to spot."
Mr Puttock said between April and October, up to 20 leisure craft could be airborne at any one time in the area and that air sports were growing into seven-day-a-week activities, not just confined to weekends.
A Ministry of Defence spokeswoman said safety was taken incredibly seriously and particularly recommendations made in an Airprox report.
She said RAF officials would be meeting gliding clubs in Wales "so lessons can be learnt".