Corrosion that led to fatigue-cracking caused the landing gear collapse on a FedEx MD-10-10F freighter at Fort Lauderdale-Hollywood International Airport, Florida, on Oct. 28, 2016, the NTSB announced.
The left main landing gear collapsed soon after the freighter touched down on Runway 10L. The aircraft yawed to the left and came to rest off the left side of the runway, where the left wing caught fire. As the two pilots prepared to evacuate, the nearly empty left main fuel tank exploded. The captain sustained minor injuries during the evacuation; the first officer was not injured.
Investigators determined the landing gear failed as a result of a metal fatigue crack that started at a corrosion “pit,” or cavity, within the gear, the NTSB said in a final accident report released on Aug. 23.
According to the report, a required, protective cadmium coating was absent where the corrosion pit formed, but the reason it was absent could not be determined from available evidence. The resulting crack went undetected and gradually worsened until the landing gear collapsed, the NTSB said.
The manufacturer’s recommended overhaul limit for the main landing gear assembly is every eight years or 7,500 flight cycles, the NTSB said. At the time of the accident, FedEx’s main landing gear overhaul limit was nine years. The outer cylinder on the accident aircraft was 152 days away from its next required overhaul.
FedEx reportedly adopted the nine-year overhaul interval used by the previous owner of the first DC-10s it purchased, the safety board said. The MD-10 has an upgraded flight deck.
“The NTSB notes that if FedEx had not adopted an overhaul limit that exceeded the manufacturer's recommendation, the fatigue crack in the accident MLG cylinder, which was last overhauled 8.5 years before the
accident, likely would have been detected and addressed before it could progress to failure,” the board said.
Contacted immediately after the NTSB announcement, FedEx issued the following statement: “Safety is our first priority. This aircraft was maintained in accordance with FAA-approved maintenance schedules and standards. As reported by the NTSB, we have made enhancements to our maintenance and inspection protocols to further enhance the safety and reliability of these aircraft.”