The US Federal Aviation Administration (FAA) is planning to carry out a series of urgent tests on both cargo and passenger versions of the 747 to assess whether the same fault is likely to develop. The flight test programme, which will be undertaken on all versions of the Boeing 747, has been ordered because of the similarities between the Amsterdam disaster and the crash last December of a China Airlines cargo 747. Both crashed shortly after taking off with a full load and after losing both right-hand engines.
In a letter to the Dutch aviation authorities, Thomas McSweeny, the deputy director of the FAA, says 'the probable cause of these two accidents appears to be related to a structural failure of the No 3 engine pylon-to-wing connection'. It has not yet been discovered which part failed but the FAA suggests 'the only possible cause is cracking and eventual failure of the mid-spar fuse pin and fittings'. These parts connect the engine to the pylon holding it on to the wing. Unfortunately, the relevant parts have not been found by investigators in either accident.
The FAA had already ordered airlines to inspect these parts in a directive issued two days after the Amsterdam crash. A spokesman for the Dutch aviation authorities said these inspections should guarantee that planes are safe until the results of the flight test programme are known. An estimated 70 people died in the Amsterdam crash after the El Al plane ploughed into a block of flats on the night of 4 October.
The inspection results show that a substantial proportion of the fuse pins have early signs of possible failure. Out of 26 aircraft inspection results, involving 416 pins, 74 have 'some degree of corrosion' and a further four have cracks in the fuse pins. One fitting was also reported to have been cracked. About half the corrosion incidents involve less than one thousandth of an inch of rust.
From analysing flight data recorder information, investigators discovered that the Amsterdam crash appears to have been caused by the No 3 (inside right) engine breaking off from the wing. Some three or four seconds later, the No 4 (outside right) engine broke off, hit by No 3. Both engines were running when they separated and there was no evidence of fire or birds' remains.
The FAA was unable to say how long the flight test programme would take or when its results would be available.
Christopher Villiers, a spokesman for Boeing, said: 'We are going to put a number of devices on between two to four aircraft to measure exactly what the loads and pressures are at all points of the flight. We are looking for airlines to co-operate with this programme, which will be carried out on normal flights.'
Although the FAA accepts that cargo versions of the 747 operate at higher maximum take-off weights than passenger aircraft, the letter says 'these loads do not significantly affect the pylon-to- wing structure'. That is why the FAA is undertaking tests on all versions of the aircraft, rather than just the 747-200F involved in both accidents.
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