Some of the research I’ve done turns out not to be Aldbourne related, but I’d like to put it on the web in case someone finds it useful.
Air Crash at Avebury 21 April 1941
P/O Siwek (A free Polish pilot) was flying a Proctor Gypsy (number P-6307), it was a training flight, he was carrying Aircraftman (2nd class) Chesnutt (from Glasgow), who was under instruction as a wireless operator. They were attached to No 9 Signal School.
At about 17:05, the Proctor was at a height of about 1400 feet when it went into a steep turn and then a left hand spin. It came of of the spin at about 300 feet, only to immediately re-commence spinning (in a flat spin). It crashed on Avebury Down about one mile South East of Avebury. Both the men were killed, Chesnutt was thrown clear by about 10-15 feet.
The investigation suggested the cause was most likely pilot error, this seems plausible as the pilot only have 16hours experience flying this type of aircraft.
P/O Siwek was buried in Yatesbury Churchyard.
[These details from from file AIR 81/6103 at the National Archives]