The 1977 Dan-Air/IAS Cargo Boeing 707 crash was a fatal accident involving a Boeing 707-321C cargo aircraft operated by Dan Air Services Limited on behalf of International Aviation Services Limited (trading as IAS Cargo Airlines at the time of the accident), which had been sub-contracted by Zambia Airways Corporation to operate a weekly scheduled all-cargo service between London Heathrow and the Zambian capital Lusaka via Athens and Nairobi.

This aircraft was also the first convertible 707 built,[2] featuring a large freight door on the left-hand side of the forward fuselage, that permitted the carriage of main deck cargo when configured as a freighter.

It was the fourth 707 the UK independent[nb 1] operated, as well as the type's second turbofan-powered and second convertible example in service with the airline.

Just before 09:30, clearance to descend to 6,000 ft (1,800 m) was granted, and moments later the plane was cleared to make a visual approach to runway 10.

This led over time to fatigue cracking in the right horizontal stabiliser's rear spar, which, due to the concealed (internal) nature of the tailplane construction, was not noticed by maintenance engineers.

The accident aircraft encountered several strong gusts during the approach immediately before the accident which, while not dangerous to a structurally sound Boeing 707, exceeded the load capable of being carried by the remaining intact spar on its own, leading to the spar eventually breaking and resulting in complete structural failure of the entire right horizontal stabiliser.

The crack found in the failed stabiliser after the accident was thought by investigators unlikely to have been detectable using normal testing means, such as fluorescent dye.