Life extension: Fatigue lifetime updating of the French Xingu fleet

Abstract

Embraer 121 Xingu is a reduced wing span version of the EMB110 "Bandeirante" with its own smaller fuselage. French Forces bought about 50 of the 105 produced aircraft. It mainly helped for the training of the transport aircraft pilots. Primary designed for passenger transport, the French use was slightly different and less severe due to lighter take-off weight and fewer pressurization cycles. This leads EMBRAER, in 1994, to give a fatigue life extension for the fleet, based on a comparison of load spectrum. The study concluded on an extension from 15 000 flight hours to 45 000. Today, the mean use has evolved and the extended potential is no longer applicable to the concerned aircraft. Therefore, the fleet needs an update of its fatigue potential, in an adaptable way taking into account that a change of the mean use could still be possible. As Embraer did not give a satisfactory answer in terms of costs or delivery time, the study was performed by a technical laboratory of the French MoD. The method consists in dividing the standard use of the aircraft in several missions and to determine by available documentation the associated solicitations. A flight test campaign enables to determine the relationship between the flight parameters and the local stress levels. Then the cumulative stress spectrum associated with the defined missions is deduced. Traditional fatigue damaging formulas based on Miner cumulative laws were finally used to compute the fatigue lifetime and appropriate safety coefficients were applied.