While on approach to Heathrow on 4 November 1967, the Caravelle descended far below the flight level assigned to it and flew into the southern slope of Blackdown Hill in West Sussex, killing all 37 on board.

[3] Flying at a shallow rate of descent, the Caravelle first clipped trees near Black Down House, then broke through a large hedge and careened across a meadow where 65 sheep were killed outright and 23 more were fatally injured.

"[3] The investigation report gave considerable attention to the possibility that the air crew could have misread their "three-pointer" altimeters, which were designed to warn the pilots with a cross hatch indicator when the altitude was below 10,000 feet.

Thus the cross hatching would have been visible to the crew for a period of about 9½ minutes before the aircraft passed through FL60 and it is a matter of conjecture whether it was still an effective warning to them at that stage of the descent.

Evidence against the possibility of simple misreading of this sort is the message from the aircraft to ATC reporting passing FL145, indicating at this time the crew knew that they were below 16,000ft.