NTSB cites hydraulic and electrical failures in FedEx 757 gear failure

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3 days ago

The National Transportation Safety Board has determined that a FedEx Boeing 757-200's belly landing in Chattanooga, Tennessee, was caused by the failure of the alternate gear extension system, which prevented the landing gear from being lowered during an emergency.
On Oct. 4, 2023, FedEx (NYSE: FDX) flight 1376 experienced an 'abnormal runway contact' when the flight crew was unable to extend the landing gear during the approach to Chattanooga's Lovell Field.
Shortly after takeoff from Chattanooga, the captain called for gear up, and the first officer raised the landing gear control lever to retract the landing gear. Both the main landing gear and nose landing gear retracted to their up and locked position. Digital flight data recorder data showed that 22 seconds after gear retraction, the hydraulic fluid quantity and pressure in the left hydraulic system began to decrease.
After troubleshooting the hydraulic issue per procedures in the Quick Reference Handbook, the flight crew made the decision to return to Chattanooga. While preparing to land, the landing gear did not extend as expected when the landing gear control lever was positioned to its down position.'Gear disagree. The gear is not coming down,' the first officer confirmed, according to cockpit voice recorder data documented by the NTSB.
Despite multiple attempts to deploy the landing gear using both normal and alternate extension systems, the crew was forced to perform a belly landing. The aircraft slid off the departure end of Runway 20 and impacted localizer antennas before coming to rest about 830 feet beyond the end of the runway.
Postaccident inspections of the landing gear system found that hydraulic fluid was leaking from the left landing gear door actuator retract hydraulic hose. Inspections also found that the engine indication and crew alerting system showed the left hydraulic system had only 32% fluid quantity remaining after the main landing gear door retraction shortly after takeoff, which is considered fully depleted.
Analysis of the failed hydraulic hose revealed multiple broken wire strands along its length and a rupture in its inner liner. The cause of the broken wire strands most likely originated from an overload event as evidenced by the necking down of the wire strands and a reduction in their area, investigators shared.More critically, electrical system inspections of the alternate extension system found no electrical continuity between the alternate gear extend switch and the alternate extension power pack. A visual examination revealed a break in a wire between the circuit breaker and the alternate gear extend switch, which prevented the system from functioning as a backup.
'Analysis of the wire's fracture surfaces showed a reduction in area and circumferential cracking of the coating, consistent with tensile loading,' the final report stated. 'No obvious defects or anomalies were observed on the fracture surfaces.'
The investigation also identified issues with the aircraft's evacuation equipment. After the airplane came to a stop, the jumpseat occupant attempted to open the L1 door, which only rotated halfway open and would not fully deploy. The R1 door also became lodged on the slide pack before the jumpseat occupant used force to open it.
Investigators found that the R1 door's bannis latch did not conform to the configuration required by an FAA Airworthiness Directive from 1986, which caused the slide pack to jam during evacuation.
The NTSB determined the probable cause of this accident to be 'the failure of the alternate gear extension system, which prevented the landing gear from being lowered. The cause of the system failure was a broken wire, due to tensile overload, between the alternate gear extend switch and the alternate extension power pack, preventing the AEPP from energizing and supplying hydraulic fluid to the door lock release actuators for the nose landing gear and main landing gear.'
Contributing to the accident was 'the loss of the left hydraulic system due to a ruptured left main gear door actuator hose from fatigue, which prevented normal landing gear operation.'
The NTSB noted that the crew of FedEx flight 1376 demonstrated good Crew Resource Management during the emergency, remaining calm and professional throughout the accident sequence. They displayed effective workload management by distributing tasks among themselves, with the captain flying and the first officer working to resolve the issue with air traffic control.
'The crew maintained clear and concise communication between all crewmembers to include a jumpseat occupant, and with ATC, actively soliciting feedback and input, and crosschecking with one another to ensure everyone was working with the same mental model,' the report stated.As a result of this investigation, the NTSB issued four new safety recommendations to the FAA and three new recommendations to Boeing on March 27, 2025. These recommendations address the need to inspect and modify bannis latches on Boeing aircraft doors and update aircraft maintenance manuals with correct configurations.
Following the accident, FedEx implemented a 275 Flight Hour check on the alternate extension system, including performing a general visual inspection while the nose landing gear and main landing gear doors are open while on the ground.
Related:
FedEx 757 accident prompts NTSB call for door latch inspections
(This article is republished from Airline Geeks.)
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