Pilots of the Kalitta Air Boeing 747-200 freighter destroyed after overrunning at Brussels rejected the take-off at about the same time as air traffic controllers observed a fire in one of the aircraft's two right-hand engines.
The aircraft overran Runway 20 by around 300m (985ft) and broke into three sections, its forward fuselage severed ahead of the main landing gear and its rear fuselage ruptured just ahead of the empennage. The 28-year-old jet also suffered substantial impact damage to its engines and underside, but the five crew escaped unhurt.
While the inquiry has not detailed any preliminary information, sources familiar with testimony to the investigation say that air traffic controllers monitoring the departure noticed flames from one of the right-hand Pratt & Whitney JT9D powerplants.
It is unclear which of the engines was seen to be affected, says the source, but he says that the airport fire brigade was alerted, adding: "At around the same time, the pilot advised the controller that he was rejecting the take-off."
The US National Transportation Safety Board has already said that a "loud bang" - the nature of which is still unclear - preceded the accident.
Tyre marks at the end of the runway and wheel tracks across the grass, extending to the wreckage site, suggest the aircraft was deviating to the right of the centreline as it overran.
Brussels airport has three runways. Its two parallels are longer than the accident runway, but the source says that Runway 20 was always the "planned runway" for the 25 May flight.
The aircraft had been bound for Bahrain with 76t of cargo, and the source points out that Runway 20 - which has a length of 2,984m - was more than adequate for the type, particularly given its relatively light load.
Recovery personnel have completed the task of emptying the 70,000kg (154,000lb) of fuel contained in the aircraft's tanks and the crash site has been declared safe.
Initial fact-finding investigations by the Belgian aviation authorities and the public prosecutor are continuing. Brussels airport says there is no indication as to the likely duration of this stage of the inquiry.
Brussels airport operations are being restricted to the two parallel runways until the 747's wreckage has been removed.