I reckon it's around 640 ft from 'the numbers' to the A15 under the final approach path at Waddo:
Which means anyone intending to touch down on the numbers, if using a normal 2½° - 3° approach, should be no lower than 27-34 ft when clearing the near edge of the road (ex-QWIs can do triggernometry, so will know that this is 640 x tan (approach angle) - n'est ce pas, Courtney?).
Spotters hanging on the fence at Brize could often be deterred by a late-notice VC10 go-around. It took a bit of practice, but if you got the timing right you could call "Simulated runway incursion, GO AROUND!" to one's student and the gentle purr of 4 Conways at max chat would be achieved just as we passed the spotter.....
