Here’s what may have happened.
Out of options he talks to Company but they can’t offer a civil solution within his range. So he calls on 121.5. First question they ask is how long a runway does he need? Simple question – Not so easy to answer off the cuff. His P3/Nav is busy taking down weather and in any case there’s little time to get the charts out and put in actual performance data. He has to be quick and very conservative, not knowing the actual conditions. I don’t know what the answer would have been but on a 707 it could easily have been 8000 (VC10 might have been 6500/7000, again conservative but he might have had to accept a small tailwind to get the vis required).
Not many 707 pilots of the time would have known off the cuff, without the time to go into charts, if they could safely get into Lyneham/Brize etc as Comets/Britannias/VC10s all had better airfield performance. They would have known that a USAF base was a safe bet.
As I wasn’t born then, yet alone flying, I can’t be sure, but you’d probably find the crew would have a number in their head that would represent a 95% (random percentage guestimate) likelihood of being an acceptable length. Calculated something like this: at Max Landing Weight on a level runway at 25 degrees (or at ISA or ISA+5 etc) with no wind we need X,000 FT.
That number would allow them to quickly appraise anything offered before checking the charts of the preferred options available.
Regardless, it’s great to see a conclusion.
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