Guys, I posted this up on the lucky escapes thread, and it was suggested I repost it on here as I am sure some of you will recall this event and my experience might be of interest.
I´ve witnessed quite a few accidents in my time, but the worst I´ve seen was the incredibly lucky escape by Barry Sheene and Jack Middleburg at Silverstone while practicing for the 1982 British GP.
There was a practice session on the Thursday before the event (official training started on Friday), which was open to all classes of bikes from 125´s to 500´s. Incredibly, there weren´t any marshals in attendance, despite the fact that almost 50 machines of varying capacity and performance were allowed onto the circuit at the same time. I was standing on the bridge over the circuit just before Woodcote (unlike the F1´s, the motorcycles didn´t used the chicane through Woodcote), looking back down the circuit towards Abbey.
Halfway through the session, a rider on a 250 fell exiting the very fast (I think flat on a 250) Abbey sweep, and both he and his motorcycle slid up the road, with the bike coming to rest diagonally across the middle of the road, about 100 meters before the bridge.
Anyone familiar with this stretch of road will know that visibility at that point is rather limited because the road crests a brow, which makes it almost impossible to see anything at ground level when the rider is flat on the tank, tucked under the fairing bubble.
Several riders passed by the stationary machine, and I could see by their reaction they hadn´t seen the bike in the road until they were almost past it.
Just as this realization dawned on me, Barry Sheene swept around Abbey, and Jack, trying to gain the maximum slipstreaming effect, was tucked in behind him with less than a few inches separating them, and riding totally blind. Barry probably saw the bike he was heading for, about 50 meters before he hit it, but at the speed he and Jack were travelling, which must have been around 260 kph, there was absolutely no time for him to react. In fact, I only saw his head starting to come out from behind the screen as he hit the machine, and he certainly hadn´t had time even shut off.
The explosion that followed as he hit the obviously full petrol tank, together with the sound of the incredible impact, not only of Barry´s machine colliding with the stationary bike, but also of Jack slamming into the rear of Barry, sounded like a bomb going off. At that point I just closed my eyes as I was positive no human could survive what I had just witnessed.
As we now know, Barry suffered quite severe leg injuries, while Jack escaped with little more than a badly sprained back.
That has to rank as the greatest escape on 2 wheels.

Top pic is the remains of Barry´s machine
Bottom pic, Jack´s bike.
Copyright. Toon Kannekens
As a footnote, that crash really ended Barry´s career IMO. It came at precicely the wrong time, what with Yamaha having just decided to give Barry equal machinery to Kenny. I think this was actually the very first time Barry or Kenny actually ever rode the Vee 4. We can only wonder how things would have developed for Barry with this machine at his disposal. Alas, it was never to be. More´s the pity.