US investigators have determined that a broken wire prevented activation of the alternate undercarriage extension system on a FedEx Boeing 757-200 freighter, forcing the crew to conduct a gear-up landing.
Some 22s after the landing-gear was retracted, shortly after take-off from Chattanooga, a fatigue rupture in the left main-gear door actuator hose resulted in the loss of hydraulic pressure.
This meant the primary landing-gear extension system could no longer deploy the undercarriage.
The pilots worked to troubleshoot the hydraulic problem and opted to return to Chattanooga. But when the crew attempted to use the alternate landing-gear system, the undercarriage still failed to extend.
According to the National Transportation Safety Board, there was “no electrical continuity” between the alternate gear-extend switch and a power pack that releases the landing-gear doors – after which the landing-gear freefalls into place.
The inquiry traced this failure to a break in a wire between the switch and a circuit-breaker, consistent with tensile loading
It states that the wire was inside a bundle, and the probability that maintenance personnel would have detected the break was “low”.
With the landing-gear unavailable, the crew prepared for a gear-up approach to Chattanooga’s runway 20.
It touched down initially on its left-hand Rolls-Royce RB211 engine about 1,650ft from the threshold, with marks from right-engine contact appearing 735ft further on.
Scraping from the aft fuselage occurred about 4,500ft from the threshold, and the aircraft overran, coming to a halt 830ft beyond the runway end.
Neither pilot, nor a third occupant on the jumpseat, was injured during the 4 October 2023 accident.
But the 757, a 1988 airframe which was converted from passenger configuration in 2015, suffered substantial damage, particularly to the engine and aft fuselage undersides.
Investigators point out that there is no inspection interval for the inside of a wire bundle, which would probably have identified a break in the alternate landing-gear system circuitry.
FedEx has since implemented a 275h check on the alternate landing-gear extension system.
