JN, if you are ever putting out a second edition and consider it worth the time /expense following the links on ASN entry for XA897 suggests the NRO has the documents. From what I have read the blame was put on the GCA controller whose last message regarding the glidepath was the a/c was 80' above and didn't communicate it was c.100' below the glidepath after correction but Howard corrected again and thought he was on the glidepath. This article
Delta Disaster: Fatal RAF Vulcan Heathrow crash states after discussion with AM Broadhurst, Sqn Ldr Howard had decided to make one approach and if unsuccessful divert to Waddington (for which there was ample fuel) and had set his break off altitude as 300' and AM Broadhurst called 450' very close to impact. It also suggests the indicated altitude was too high:
Error margin
As it turned out, a whole bevy of Master Greens on XA897’s flightdeck would have added little extra safety margin. Although the GCA at Heathrow was a first-generation system that was much cruder than modern landing aids, the full vindication of Howard and Broadhurst had to await the inquest on January 30, 1957.
Despite Howard's lack of instrument experience on the Vulcan, the RAF could not credit that he would have gone so far below his break-off height without realising it or that both he and Broadhurst would have misread their altimeters so wildly.
A scientific study of Vulcan altimeter errors was undertaken at Boscombe, which revealed the large delta wing area created its own atmospheric pressure error of between 70-130ft when close to the ground. Friction within the altimeter could add a further 70ft, making a total possible error of 200ft. Add this to Runway 10 Left’s elevation of 80ft above sea level and it becomes clear that with 300ft indicated on his altimeter, Howard was already among the weeds.
There need have been no sudden and unaccountable descent as postulated by Dr Touch. The Vulcan's gentle 3° descent on the GCA glidepath would soon have swallowed up the tiny safety margin remaining to the pilots of XA897. On all future Vulcan instrument approaches, pilots would be briefed to add an extra pressure error correction factor, but it was a pity it took the tragedy at London Airport to bring the lesson to everyone's attention in the first place.
The BOI president was ACM Sir Donald Hardman, Air Member for Supply and Organisation and previously CAS, RAAF.
Can any of our resident Vulcan aircrew confirm 'pilots would be briefed to add an extra pressure error correction factor'?