What happened
On October 4, 2023, a Boeing 757-236 operated by FedEx, registration N977FD, departed Chattanooga, Tennessee, for Memphis, Tennessee. Shortly after takeoff, the aircraft experienced a failure in its left hydraulic system. The flight crew subsequently turned the aircraft back toward Chattanooga.
During the approach, the crew attempted to extend the landing gear but found it would not descend. While the crew successfully used the normal gear extension process for the nose and main gear earlier in the flight, the gear failed to unlock and extend during the landing phase. The crew attempted to use the alternate gear extension system multiple times, but the gear remained retracted. After a low-altitude pass to allow ground personnel to visually inspect the gear, the crew proceeded with the landing.
Upon landing on runway 20, the aircraft was unable to stop within the runway limits. The airplane slid off the departure end of the runway, impacted localizer antennas, and came to rest approximately 830 feet beyond the pavement. The aircraft sustained substantial damage, but the two flight crewmembers and one jumpseat occupant were not injured.
The investigation
Investigators examined the hydraulic system and found that the left hydraulic system fluid quantity had dropped to 32% shortly after takeoff. The leak was traced to a ruptured hydraulic hose on the left main landing gear door actuator. Examination of this hose revealed broken wire strands in the external braid and a tear in the inner PTFE liner, with findings consistent with tensile overload.
Regarding the failure of the alternate extension system, investigators found an electrical break in a wire located inside a wire bundle between the alternate gear extend switch and the alternate extension power pack. This break was also consistent with tensile loading.
An examination of the exit doors revealed two different issues during the evacuation. The L1 door failed to open fully because a deployment strap had been misrouted. The R1 door was difficult to open because the bannis latch assembly did not conform to required configurations, causing the slide pack to jam temporarily.
Findings
- The left hydraulic system lost pressure due to a ruptured actuator hose.
- The alternate gear extension system failed to function because of a broken wire between the switch and the power pack.
- The R1 door latch assembly was non-compliant with existing Airworthiness Directives, which hindered the evacuation process.
- The L1 door evacuation was obstructed by a misrouted deployment strap.