I used to witness and photograph many Harrier & Hawk engine runs, as I was a photographer at Dunsfold, Surrey where they originated.
Seeing a Harrier run at anywhere near full throttle was something else - like watching a very p'd off T. Rex on a short leash !
We were in a 3 walled engine pen, the aircraft held down by huge bottlescrews and chains.
There was a double sided wall containing the telemetry equipment, and an armoured glass window.
The engineers conducting the runs were always Rolls Royce rep's,( 2 were resident with us at any given time ) in the cockpit in their shirtsleeves; so if anything nasty happened, they could not eject - though that may well have meant landing on any fire in their 'chutes, without even a Nomex flying suit.
There was always a fire engine standing by, with the award winning Dunsfold Fire & Rescue team, now sadly some working as security guards -The airfield is where 'Top Gear' is filmed now, and Mercedes train rich idiots to drive their McLaren supercar.
There was an occasion, early on in P1127 / Kestrel / Harrier development, when an aicraft under such tests broke free, giving the engineer the ride of a lifetime before it broke the noseleg and stopped, probably by his frantic pulling at HP & LP cocks etc !
After that, the Harrier engine run pen ( which is basically a grid with ducting underneath to take the thrust if nozzles were checked ) was strain tested at regular intervals with a load cell on the largest mobile crane I've ever seen.
Other websites can't be advertised, but if you were to dial Harrier/History into a search engine, then scroll down to 'Harrier Testing'...however you may be more into airliners.
Unfortunately I don't have photo's of Harrier runs I was stupid enough to leave them on file when I upped and left, but do have some copied pic's of the Harrier in pen & my shots of the original Hawk 200 - in which the brilliant Test & Display Pilot Jim Hawkins came to a sad end - in the pen just before it's first flight, being run up by R.R. Engineer Keith Wardel.
If of any interest, mail me & I'll pass them on;
[email protected]