BOEING 757-236

Full Narrative

HISTORY OF FLIGHTOn October 4, 2023, about 2347 eastern daylight time (EDT), FedEx flight 1376, a Boeing 757-236, sustained a failure of its left hydraulic system shortly after takeoff from CHA. The airplane turned back to CHA, and, while preparing to land, the landing gear failed to extend normally. The landing gear also failed to extend using the alternate extension system. The flight crew declared an emergency and the airplane sustained substantial damage during the emergency landing. The two flight crewmembers and a jumpseat occupant onboard the airplane were not injured. The flight was operating under the provisions of Title 14 Code of Federal Regulations (CFR) Part 121 as a non-scheduled domestic cargo flight from CHA to Memphis International Airport (MEM), Memphis, Tennessee.

According to postaccident flight crewmember statements, the airplane had no maintenance issues before the flight, and the push-back, engine start, and taxi were all uneventful. The captain was the pilot flying, and the FO was the pilot monitoring.

CVR data indicated that the flight was cleared for takeoff by the CHA local control (LC) controller at 2221:54 EDT. The Runway Awareness Advisory System (RAAS) announced “On runway two zero” at 2222:58, and the engines were audible accelerating to high power shortly afterward. As the aircraft accelerated, the FO made the following callouts: thrust set, eighty knots, V1, rotate, and positive rate. DFDR data showed that the gear weight-on-wheels transitioned from ground to air at about 2223:42. The captain called for gear up at 2223:44 and the FO raised the landing gear control lever to retract the landing gear. DFDR data showed that the landing gear lever handle was moved to its up position at 2223:47. The flight crew indicated that both the MLG and the NLG retracted to their up and locked positions. The completion of nose gear retraction was audible in the flight deck at 2223:58. DFDR data indicated that 11 seconds later, at 2224:09, the hydraulic fluid quantity and pressure in the left hydraulic system began to decrease. A left hydraulic system low quantity indication and master caution were recorded shortly thereafter (figure 1)

At 2224:17, CVR data indicated that the captain said, “Left hydraulic quantity.” At 2224:32, a caution beeper was audible while the FO communicated with the CHA approach controller. The captain called for flaps up and asked the FO to ask ATC to “see if we can just maintain runway heading.” A click consistent with flap handle movement was audible at 2224:47, followed by another caution beeper at 2224:52, and the captain stated, “Flaps disagree.” According to postaccident flight crewmember statements, immediately after placing the flap handle to its up (flaps 0) position, a TE FLAP DISAGREE message was displayed on the EICAS, along with an associated master caution light, a TRAILING EDGE discrete light, and the aural alert caution beeper.


Figure 1. Plot of the FDR data from the event takeoff.

At 2225:01, the captain said, “Autothrottles are off.” The FO reported to ATC that they were working an issue and requested permission to maintain the runway heading up to 5,000 ft, which was approved. Per the captain's direction, the FO began accomplishing the TE FLAP DISAGREE checklist in the QRH. CVR data indicated that the left hydraulic system pressure QRH items were completed at 2229:12, and the captain asked the FO to send the FedEx operations department a text informing them of the aircraft’s condition and asking whether they should return to Chattanooga or continue to Memphis. At 2230:53, the crew checked over the QRH checklist for the Trailing Edge Flap Disagree message. Both the TE FLAP DISAGREE and the Hydraulic System Pressure (L only) checklists indicated using Flaps 20 and Vref 20 for landing. Following the checklist, they set flap alternate modes for leading and trailing edge flaps and the FO completed landing performance calculations for the planned alternate landing configuration. They also discussed fuel state and determined that returning to Chattanooga would be the appropriate decision.

At 2237:10, the captain informed ATC of their need to return to Chattanooga and that they would still need some time to work checklist items before returning. The controller provided vectors to keep them north of the airport and asked if they would like to declare an emergency, which the captain declined. The crew continued to work together to complete appropriate checklists and input performance calculations for the aircraft’s non-normal condition into the flight management computer (FMC).

At 2246:30, the crew selected flaps 1 using the alternate flaps system and requested vectors from ATC for their instrument landing system (ILS) approach into Chattanooga runway 20. As they maneuvered for the approach the crew slowed and configured the airplane for landing through flap settings. Flap movements were slower than normal, which was expected due to the alternate configuration.
 
CVR data indicated that, at 2249:45, they reached their planned approach flaps configuration of 20 degrees and attempted to lower the landing gear. A triple chime was audible at 2249:50, and the captain said, “Gear disagree.” The first officer confirmed, “Gear disagree. The gear is not coming down.” At 2250:15, the captain contacted ATC to break off their approach and reported that they had an unsafe gear indication. Following the failed attempt to lower the landing gear, the crew went methodically through the Hydraulic System Pressure (L only) QRH checklist to determine the next steps. The crew determined that they would attempt an alternate gear extension. Because the checklist informed them that nose wheel steering would be inoperative following the alternate gear extension and the aircraft would not be able to clear the runway on its own, the crew declared an emergency with ATC at 2253:30. At 2254:34, the crew attempted the alternate gear extension procedure, and they verbalized that there were no lights indicating that the gear was down. The crew completed the procedure several more times over the next 7 minutes, including re-completing the Hydraulic System Pressure checklist in full. 

At 2301:17, the crew brought the jumpseat occupant, who was another FedEx pilot, to the flight deck. The crewmembers and jumpseat occupant talked through the issues and troubleshooting that had been done so far and decided to radio FedEx operations to speak with a maintenance technician. While waiting for the technician they discussed their fuel remaining and made a fuel plan for when they would have to commit to landing.

At 2311:05, the flight crewmembers asked Chattanooga approach if they could conduct a low approach over the runway so that tower personnel could visually confirm the position of the landing gear. The airplane descended to about 150 ft above ground level and flew the length of the runway, which was followed by a go-around. Approach control relayed confirmation that the landing gear was not in the down position.

At 2326:22, the FedEx maintenance technician provided them two circuit breakers to cycle in an attempt to lower the landing gear with the alternate extension procedure, which was unsuccessful.

As the crew set the aircraft up for the final approach, they continued following the Gear Disagree checklist and worked other appropriate standard checklists as dictated by flight conditions. The flight was cleared to land by the tower at 2339:40. The captain briefed the FO that he was planning to aim close to the runway threshold and the FO verbally updated the captain on wind conditions and airspeeds. They agreed that the jumpseat occupant would open the L1 door when they landed. Initial audible indications of ground contact occurred at 2347:10, the RAAS reported 500 ft remaining at 2347:30, and audible indications of runway departure occurred at 2347:35. The recording ended three seconds later at 2347:38
 
The flight crew was unable to stop the airplane, and it slid off the departure end of runway 20 and impacted localizer antennas before coming to rest about 830 ft beyond the end of the runway (see figure 2).

 
Figure 2. Drone photograph of the airplane at the accident site. (Source: Aircraft Rescue and Fire Fighting)

After the airplane came to a complete stop, the flight crew performed the evacuation checklist in the QRH, and the jumpseat occupant attempted to open the L1 door (see figure 3, upper photo). The door rotated halfway open but would not open fully, and the slide did not deploy. The jumpseat occupant then attempted to open the R1 door, but it lodged on the slide pack. The jumpseat occupant used force to open the R1 door, and the slide deployed normally (see figure 3, lower photo). The flight crew and the jumpseat occupant exited the airplane through the R1 door and slide. Both flight crewmembers and the jumpseat occupant were uninjured. The event was classified as an accident because the airplane sustained substantial damage. 

 


 
Figure 3. Photos of the airplane in its final resting position. (Source for upper photo: Chattanooga Fire Department; source for lower photo: FAA) AIRCRAFT INFORMATIONLanding Gear / Hydraulic System:

The Boeing 757 is equipped with three independent hydraulic systems: the left, right, and center. The left and right hydraulic systems are each powered by an engine-driven pump (EDP) and an alternating current motor pump (ACMP). The center system is powered by two ACMPs.

The hydraulic system incorporates a power transfer unit (PTU), which has a hydraulic motor pump and transfers hydraulic power from the right system to the left system. The PTU is automatically activated when the left EDP pressure is low or the left engine fails. When activated, the PTU powers a dedicated portion of the left hydraulic system, which operates the flaps and slats, landing gear, and nose wheel steering. If the PTU fails to develop pressure in the left system (as expected following the loss of left system hydraulic fluid), the pressure switch for the PTU senses the lack of system pressure and will command the PTU off. The PTU cannot be controlled by the flight crew in the flight deck.

The MLG and NLG are hydraulically retracted and extended under normal conditions by the left hydraulic system. The MLG and NLG can also be powered as mentioned above by the right hydraulic system through the PTU.

To extend the landing gear, a flight crewmember must move the landing gear control lever out of its detent and position it to its down position. Lever movement is transmitted via control cables to the landing gear selector valve. Operation of the valve supplies hydraulic pressure through the extension hydraulic lines to extend the landing gear and operate the landing gear doors.

When there is a loss of left hydraulic system pressure (for example, due to a loss of fluid), the landing gear doors cannot be opened, and the landing gear cannot be lowered using the normal gear extension system. In such a case, the landing gear may be extended using the alternate landing gear extension system. This system uses a dedicated hydraulic circuit within the left hydraulic system to release the uplocks on the landing gear doors and gear when activated. To extend the gear with this system, a flight crewmember would move the ALTN GEAR EXTEND switch (a guarded switch) to the down position. When the switch is moved to down, two alternate extension control relays are energized: one relay supplies power to a latching circuit and the other sends power to the alternate extension power pack (AEPP) to start the alternate gear extension. The ALTN GEAR EXTEND switch is a momentary switch, spring-loaded to the OFF position. When energized, the AEPP supplies hydraulic fluid to the door lock release actuators for the NLG and MLG and a hydraulic pressure switch commands off the AEPP electric motor pump. These actuators extend and mechanically release the internal locks in the door actuators.

When activated, the doors and landing gear begin to free-fall to the down-and-locked position. This system is also used to open the landing gear doors for maintenance procedures in or near the wheel well areas.

Doors:
The accident airplane was converted from a passenger configuration to a cargo configuration for FedEx in 2015. The airplane had two floor-level (Type I Exit) doors behind the cockpit (L1 and R1) that allowed entry to the airplane and a means of evacuation if necessary. Doors 2L, 2R, 3L, 3R, 4L, and 4R were deactivated as part of the cargo conversion. The conversion also included installing a large main deck cargo door on the forward left side and two lower deck cargo doors on the forward and aft right side.

The door system consisted of a door, a door handle, an arming lever, a slide/raft pack, a girt bar, and an emergency power assist system (EPAS). Once the door is closed using the door handle, a flight crewmember slides the arming lever over into the red area, arming it, and the door armed indicator pops out on the door. The girt bar is attached to the floor fittings by the bar locks when the door is armed.

If the door is opened while armed, the slide/raft will deploy. This is a complex system that begins when an occupant rotates the door handle. Once the door reaches a certain point during opening, the EPAS, a pressurized system with one bottle per door that assists the door opening in an emergency, is triggered, which then aids in the door rotating outward. The EPAS only discharges when the door is in the armed position, and does not discharge during normal door operation. Postaccident examination of the EPAS found that both the left and right door power-assist bottles were depleted.

The girt bar, which secures to the floor fitting during the closing and arming process, has an escape slide harness latch assembly attached to it and the harness securing the slide/raft pack to the door. This is a directionally sensitive latch system that will only release because of a horizontal pull, which would be initiated if the door was opening with the girt bar still secure in the floor fittings.

When the door is mostly open and the escape slide latch releases, the harness no longer supports the slide/raft and the slide pack begins to drop downward. This downward motion then pulls the cover release pins on the slide/raft pack, allowing the slide to drop and the pressure bottleor inflation to discharge. The slide is then inflated, allowing the occupants to evacuate. AIRPORT INFORMATIONLanding Gear / Hydraulic System:

The Boeing 757 is equipped with three independent hydraulic systems: the left, right, and center. The left and right hydraulic systems are each powered by an engine-driven pump (EDP) and an alternating current motor pump (ACMP). The center system is powered by two ACMPs.

The hydraulic system incorporates a power transfer unit (PTU), which has a hydraulic motor pump and transfers hydraulic power from the right system to the left system. The PTU is automatically activated when the left EDP pressure is low or the left engine fails. When activated, the PTU powers a dedicated portion of the left hydraulic system, which operates the flaps and slats, landing gear, and nose wheel steering. If the PTU fails to develop pressure in the left system (as expected following the loss of left system hydraulic fluid), the pressure switch for the PTU senses the lack of system pressure and will command the PTU off. The PTU cannot be controlled by the flight crew in the flight deck.

The MLG and NLG are hydraulically retracted and extended under normal conditions by the left hydraulic system. The MLG and NLG can also be powered as mentioned above by the right hydraulic system through the PTU.

To extend the landing gear, a flight crewmember must move the landing gear control lever out of its detent and position it to its down position. Lever movement is transmitted via control cables to the landing gear selector valve. Operation of the valve supplies hydraulic pressure through the extension hydraulic lines to extend the landing gear and operate the landing gear doors.

When there is a loss of left hydraulic system pressure (for example, due to a loss of fluid), the landing gear doors cannot be opened, and the landing gear cannot be lowered using the normal gear extension system. In such a case, the landing gear may be extended using the alternate landing gear extension system. This system uses a dedicated hydraulic circuit within the left hydraulic system to release the uplocks on the landing gear doors and gear when activated. To extend the gear with this system, a flight crewmember would move the ALTN GEAR EXTEND switch (a guarded switch) to the down position. When the switch is moved to down, two alternate extension control relays are energized: one relay supplies power to a latching circuit and the other sends power to the alternate extension power pack (AEPP) to start the alternate gear extension. The ALTN GEAR EXTEND switch is a momentary switch, spring-loaded to the OFF position. When energized, the AEPP supplies hydraulic fluid to the door lock release actuators for the NLG and MLG and a hydraulic pressure switch commands off the AEPP electric motor pump. These actuators extend and mechanically release the internal locks in the door actuators.

When activated, the doors and landing gear begin to free-fall to the down-and-locked position. This system is also used to open the landing gear doors for maintenance procedures in or near the wheel well areas.

Doors:
The accident airplane was converted from a passenger configuration to a cargo configuration for FedEx in 2015. The airplane had two floor-level (Type I Exit) doors behind the cockpit (L1 and R1) that allowed entry to the airplane and a means of evacuation if necessary. Doors 2L, 2R, 3L, 3R, 4L, and 4R were deactivated as part of the cargo conversion. The conversion also included installing a large main deck cargo door on the forward left side and two lower deck cargo doors on the forward and aft right side.

The door system consisted of a door, a door handle, an arming lever, a slide/raft pack, a girt bar, and an emergency power assist system (EPAS). Once the door is closed using the door handle, a flight crewmember slides the arming lever over into the red area, arming it, and the door armed indicator pops out on the door. The girt bar is attached to the floor fittings by the bar locks when the door is armed.

If the door is opened while armed, the slide/raft will deploy. This is a complex system that begins when an occupant rotates the door handle. Once the door reaches a certain point during opening, the EPAS, a pressurized system with one bottle per door that assists the door opening in an emergency, is triggered, which then aids in the door rotating outward. The EPAS only discharges when the door is in the armed position, and does not discharge during normal door operation. Postaccident examination of the EPAS found that both the left and right door power-assist bottles were depleted.

The girt bar, which secures to the floor fitting during the closing and arming process, has an escape slide harness latch assembly attached to it and the harness securing the slide/raft pack to the door. This is a directionally sensitive latch system that will only release because of a horizontal pull, which would be initiated if the door was opening with the girt bar still secure in the floor fittings.

When the door is mostly open and the escape slide latch releases, the harness no longer supports the slide/raft and the slide pack begins to drop downward. This downward motion then pulls the cover release pins on the slide/raft pack, allowing the slide to drop and the pressure bottleor inflation to discharge. The slide is then inflated, allowing the occupants to evacuate. WRECKAGE AND IMPACT INFORMATIONThe airplane landed at CHA with both the left and right MLG and the NLG fully retracted. The initial runway contact was indicated by ground marks consistent with the left engine on the left side of the runway 20 centerline approximately 1,650 ft from the runway 20 threshold bar. The ground marks were light at first and progressed in intensity. At 2,385 ft from the runway 20 threshold bar, defined “skipping” marks consistent with both engines were seen on both sides of the runway centerline. The skipping/scraping marks continued until they turned into a continuous dark line on both sides of the centerline and near the centerline due to the tail contacting the runway. The start of this change was at 4,500 ft from the runway 20 threshold bar. The marks were parallel to the centerline. At 5,300 ft from the runway 20 threshold bar, the marks bent slightly to the right before straightening out again. When the airplane passed the end of the runway 20 pavement, the number 1 engine nacelle marks were just left of the runway centerline. The ground scars continued into the grass area at the end of the runway and paralleled the extended runway centerline. The airplane stopped at N 35°01'13.64", W 85°12'29.87" (approximately the middle of the airplane) on a heading of 180°, and about 830 ft beyond the edge of the pavement for the departure end of runway 20 (see figures 4 and 5).


Figure 4. Runway diagram with notes of airplane scrape marks along runway 20, according to airport operations.


Figure 5. Airplane’s final location after landing.

Postaccident inspection of the flight deck found that the L ENG (left engine) hydraulic pump and L ELEC (left electric) hydraulic pump switches were in the OFF position. The R ENG (right engine) and R ELEC (right electric) hydraulic pump switches were found in the ON position. The center electric pump switches 1 and 2 were in the ON position.

The landing gear control lever was found in the down position and the ALTN GEAR EXTEND switch was found in the OFF position with its guarded cover open. The ALTN FLAPS knob was found positioned to 20. The LE (leading edge) and TE (trailing edge) switches were found in the ALTN position. The flap Indicator needle indicated 20.

In the early morning of October 6, the investigative team witnessed the FedEx recovery experts lift the aircraft with cranes in order to deploy the landing gear. Once lifted, FedEx maintenance personnel attempted to extend the landing gear using the alternate extension system. However, when the ALTN GEAR EXTEND switch was moved to its down position, the landing gear doors did not open and the MLG and NLG did not extend. Additionally, there was no indication that the alternate extension power pack was operating. The airplane hydraulic pumps had been turned ON during this attempt to extend the gear and the following hydraulic system fluid quantities were noted on the EICAS page: 0.32 left, 0.95 center, and 0.95 right. The quantities are displayed in percentages, therefore 0.32 indicated that the left system had 32% of its fluid remaining.

The maintenance personnel attempted to service the left hydraulic system reservoir, but when hydraulic fluid was pumped into the left system, hydraulic fluid was observed to be leaking from the left landing gear door area. The left landing gear door was manually opened by physically activating the door uplock mechanism (a nonstandard method). The maintenance personnel again serviced the left hydraulic reservoir and observed fluid leaking from the left landing gear door actuator retract hydraulic hose. The hose, in the as-found position, was not contacting any surrounding structure or other components.

The failed hose was removed and quarantined for further examination. A new hose was installed, and the left hydraulic system was serviced with no additional leaks observed. The hydraulic pumps were selected ON and the landing gear was selected down using the landing gear control lever. The landing gear extended normally; however, the alternate gear extension system remained non-functional. The aircraft was towed back to the pavement of runway 20 and then to the FedEx ramp.

The failed hose was sent to the Boeing EQA lab for further examination. One end of the hose had a straight fitting, while the opposite end had a 90-degree fitting. According to the identification tag on the hose, it was manufactured in March 1987. Examination of the hose revealed broken wire strands of the external corrosion-resistant steel (CRES) braid, just beyond the straight-end fitting. Multiple broken CRES wires were also found throughout the entire length of the hose. Images were captured showing some of the broken wire strand ends near the ruptured portion of the hose (see figures 6 and 7). No corrosion or discoloration was observed on the hose.


Figure 6. Exposed wire braid strands. (Source: Boeing)




Figure 7. Exposed wire braid strands. (Source: Boeing)

Microscopic examination was performed on the broken wire strands adjacent to the rupture in the hydraulic hose. The fracture surfaces showed a reduction in area and necking. These features were consistent with tensile overload. No other obvious defects or anomalies were observed.

A borescope examination of the internal portion of the hose was performed. A tear in the PTFE inner liner was observed approximately two inches from the end of the straight-end fitting (see figure 8). This tear is in the area of broken wire braid strands. Some CRES wires were visibly protruding through the tear in the PTFE inner liner. No contamination or other anomalies were observed inside the hose.


Figure 8. Borescope image showing the tear and protruding wire strands. (Source: Boeing)

The subject hydraulic hose is covered in the MSG-3 Zonal Inspection as part of a General Visual Inspection (GVI) Task.  GVI is defined as a visual examination of an interior or exterior area, installation or assembly to detect obvious damage, failure or irregularity.  This level of inspection is made from within touching distance, unless otherwise specified.  The airplane accident had no history of replacements for the hydraulic hose since FedEx took delivery of the airplane in 2013. FedEx did not have any records of the hydraulic hose before delivery.

As previously stated, the landing gear alternate extension system did not function as required during the accident flight or the initial examination of the airplane. Electrical system inspections of the alternate extension system found no electrical continuity between the ALTN GEAR EXTEND switch and the AEPP. A visual examination of the alternate extension system wiring revealed a break (open) in a wire between the circuit breaker and the alternate gear extend switch. To identify the failure mode of the wire, the broken wire was cut on both ends of the wire break and the two pieces were removed from the airplane. For identification, one wire was labeled as “separate wire” and the other as “splice wire. Both pieces were sent to the Boeing EQA in Seattle, Washington, for examination. The wire remaining on the airplane was temporarily repaired and operation of the alternate landing gear extension system was retested and found fully functional.

On November 7 and 8, 2023, an examination of the “separate wire” and the “splice wire” was conducted at the Boeing EQA in the presence of the NTSB. The failed ends of both sections of wires were examined using a digital microscope. Both wires were then sent to the Boeing Research & Technology (BR&T) metallurgy lab for fracture analysis. Scanning electron microscopic (SEM) images were taken of both the “separate wire” and “splice wire.” The fracture shape showed a reduction in area and circumferential cracking of the coating, consistent with tensile loading. No obvious defects or anomalies were observed on the fracture surfaces (see figure 9).


Figure 9. “Splice wire” showing area of reduction. (Source: Boeing)


Exit Doors:

After the airplane came to a stop, the jumpseat occupant reported that he grabbed paperwork then went to the L1 door and attempted to open it. The door opened about halfway and he was unable to open it any further. The slide/raft did not release from the door and did not deploy. He then moved to the R1 door, which caught on “something,” but he was able to “kick” it open, at which point the slide deployed.

On October 5, 2023, before maintenance from FedEx entered the airplane, an FAA representative along with FedEx maintenance personnel disengaged the L1 girt bar from the floor fittings, and let it hang from the door. A visual inspection of the door and its slide assembly revealed that the slide pack remained in place (it had not started to fall from the door) and it appeared that the slide release mechanism had not activated (see figure 10). An FAA representative reported to the NTSB Survival Factors group chair that, while the airplane was still resting on its belly, he pushed the L1 door open through significant resistance, which he estimated at about 60–80 lbs. Once the airplane was back on the landing gear, the NTSB airworthiness group representatives cycled the door about three times with no binding noted.


Figure 10. L1 door position when ARFF arrived (left), L1 fully opened later (right). (Source: FAA)

On October 18, 2023, the NTSB Survival Factors group convened at CHA to inspect the L1 and R1 exit doors. At the time of their inspection, the airplane was parked, with its landing gear extended, and on the FedEx ramp at the airport to allow for further documentation.


Door L1:

Survival Factors group found the L1 door in its closed position. After the group visually inspected the door and evacuation slide, the door was opened from the inside. The door opened normally without any binding. No fresh rubbing or contact marks were noted around the door frame, the hinges, or the door itself. The door was then opened and closed multiple times while unarmed.

The door was armed and unarmed repeatedly by a Boeing representative. The armed indicator just above the door handle did not pop out; however, it was popped out when the NTSB survival factors investigators arrived. The door was then opened and closed, while armed, multiple times to listen if the EPAS system would activate. Each time a sound indicating activation of the EPAS mechanism to discharge was heard.

The L1 slide was found still attached to the door with the girt bar unsecured to the girt bar floor fittings. According to the representative from the Air Line Pilots Association, the slide pack cover was partially removed to allow access to the slide/raft pressure bottle to insert the safety pin into the regulator and render it safe.

The lower strap for the slide harness was found mis-routed through the release strap/latch chain buckle spacers (see figure 11).


Figure 11. L1 harness strap mis-routed.

The slide/raft pack harness was found secured to the door. The bracket on the harness forward side (when the door is in the closed position) was released from the escape slide latch. However, the opposite aft side was still attached. The latch was fully pulled to the forward side (see figure 12). The latch assembly pins were extended and locked, and the harness bracket was deformed. The harness bracket was manipulated with a screwdriver, releasing the latch and freeing the slide pack.


Figure 12. L1 escape slide latch block assembly and shelf bracket as found on October 18, 2023.

Once the slide cover was removed a visual inspection of the L1 slide pack was performed. It was noted that the parachute pins on the aft (left hand) lacing cover release cable had come out of their cones, but the forward pins were still secured (see figure 13).

Side Cover Pin Attached
Aft Side Cover Released
Figure 13. Slide pack and harness with the door shut and girt bar disconnected.





Door R1:

When NTSB investigators arrived at the CHA airport on October 5, 2023, the R1 door was open, and the slide was deployed. The R1 slide/raft harness, which secures it to the door, was still attached to the door, and the escape slide latch assembly was attached to the R1 slide, which had been removed by FedEx maintenance with the supervision of the NTSB Airworthiness group before the airplane was lifted onto its landing gear.

Although the R1 slide deployed, inflated, and was used during the evacuation, the jumpseat occupant indicated in his postaccident statement that it became “hung up on the raft/slide bulge” when he tried to open it. Using force, the jumpseat occupant was able to push the door open, allowing the slide to drop from the door, deploy, and inflate. The slide remained inflated until NTSB investigators deflated it on October 6, 2023. When the escape slide latch assembly was removed from the R1 slide/raft it was noted that the latch assembly was different than that on the L1 door.

Postaccident examination of the R1 door found that its bannis latch (which releases the slide pack when an armed door is opened) did not conform to the then-current configuration of the release cable assembly. Specifically, the assembly is supposed to have three links added with two spacers and hardware, as required by FAA AD 86-09-09 by reference to Boeing SB 757-25A0058, dated April 18, 1986. Instead, the R1 bannis latch on the accident airplane had only one link and lacked other required hardware, which caused the slide pack to jam before the jumpseat occupant was eventually able to force the door to open. When the R1 and L1 escape slide latch assemblies were compared, there were differences noted in the number of spacer links (see figure 14).


Figure14. L1 (left) and R1 (right) escape slide latch assemblies. (Source: Boeing)

During a production line functional test on L2 in 1985, the escape slide latch prematurely released, dropping the slide pack inside the airplane. This resulted in the opened slide cover jamming in the door cutout, which prevented further door opening. On April 18, 1986, Boeing issued SB 757-25A00058. This modified the escape slide pack release cable assemblies to increase the effective length of the cable by incorporating extension links to passenger doors 1 and 2 (see figure 15). The Boeing SB also required the incorporation of Air Cruisers SB 105-25-17, dated April 18, 1986, which makes the link installation compatible with the escape slide pack by adding a guide ring for cable/strap routing. This change did not apply to passenger door 4. On May 30, 1986, the FAA issued an AD for all 757-200 airplanes mandating the incorporation of the Boeing SB within 45 days. The accident airplane was manufactured and delivered in 1988 (post-AD) and therefore should have had modified latch assemblies.

Figure 15. Escape slide latches pre (left) Assembly P/N 65C19901-4 and post (right) Assembly P/N 65C19901-19 (which does not include the 2 links, 2 bolts, 2 spacers, and 2 nuts) application of the 1986 Boeing and Air Cruisers SBs.

After reports of fraying in the latch cable, the FAA issued AD 90-12-11R1 on July 31, 1990. The AD was applicable to Boeing 727, 737, and 757 airplanes with evacuation slides and mandated a visual inspection within 45 days and continued repetitive visual inspection of all latch cables at a 12-month interval. To solve the fraying issue, Boeing issued SB 757-25A0108 on February 21, 1991, which replaced the cable (P/N 69-49956-13) with a chain (P/N 65C19901-21) and split ring (P/N BACR12BU9B), which was soldered after installation to prevent inadvertent removal (see figure 16). Operators choosing to comply with SB 757-25A0108 were no longer required to comply with AD 90-12-11R1, thus eliminating the 12-month inspection requirement.


Figure 16. Chain and split ring (left) replacement for the cable (right).

Operators with reported corroded spring pins and unserviceable split rings in the latch assemblies resulted in Boeing issuing SB 757-25-0217, dated May 25, 2000. On August 28, 2001, the FAA issued AD-2001-15-01, which mandated Boeing SB 757-25-0217. Additionally, the AD required prior or concurrent incorporation of Boeing SB 757-25A0108 Rev 1, dated June 25, 1992, which modified the latch assembly of escape slides with the chain to replace the soldered split rings with a clevis and rivet (see figure 17). Additionally, spring pins in the latch assembly became corroded and needed to be replaced.


Figure 17. Escape slide latch with chain and split ring (left). SB 757-25A0108 replaced spring pins, and the split ring with a clevis and rivet (right). Current configuration Assembly P/N 65C19901-41.





FedEx Postaccident Inspections

After the CHA accident, FedEx inspected the L1 and R1 doors on the 97 other airplanes in its Boeing 757 fleet and found no other instances of a misrouted deployment strap. However, the inspection found 46 doors (about 24%) that were not compliant with either AD 86-09-09 or AD 2001-15-01 (applicable to Boeing 727, 737, and 757-200, -200CB, and -300 series airplanes because these models used the same bannis latch design). AD 2001-15-01 required bannis latch modifications recommended in two other Boeing SBs applicable to 757 airplanes (757-25A0108 and 757-25-0217). The diagrams in each successive AD and SB indicated the modifications to the configuration covered in that document but missed parts of prior modifications so that none of the diagrams were fully correct. As a result of FedEx’s fleet inspection findings, Boeing issued a multi-operator message (MOM-MOM-24-0199-01B[R1]) on April 8, 2024, which notified operators to inspect the door 1 and door 2 escape slide latch assemblies for the proper configuration. Boeing subsequently received notification from a non-US operator that its inspection of four 757 doors found three with bannis latches that did not comply with ADs 86-09-09 and 2001-15-01.

The accident airplane was manufactured in 1988 and should have been delivered with bannis latches that complied with AD 86-09-09. It is currently unknown why noncompliant components were present at the time of the accident. The accident airplane was operated by multiple carriers before FedEx acquired it, and the NTSB does not have maintenance records for these other carriers. Although the R1 door was eventually opened despite the incorrectly configured latch, the NTSB is concerned that it hindered an emergency evacuation.

The NTSB’s review of the Boeing 757 and FedEx aircraft maintenance manuals (AMMs) and the Boeing illustrated parts catalog (IPC) found that all contained inconsistent depictions of the bannis latch configuration as required by ADs 86-09-09 6 and 2001-15-01. None of these resources depict the bannis latch with all required modifications. These inconsistent, conflicting depictions would likely be confusing to maintenance personnel and could lead to the installation of and failure to detect nonconforming latches, which could result in another incident of an evacuation slide not deploying properly when needed. After the NTSB urged Boeing to look into the high incidence of noncompliant in-service bannis latches that were identified during FedEx’s fleet inspection, Boeing’s revision groups for the 757 AMM and IPC reached a consensus that the correct hardware for the bannis latch assembly could be clarified.


Boeing Actions

Based on the initial findings in the accident, Boeing issued a MOM on April 8, 2024. This MOM addressed the incorrect escape slide latch assembly configurations and provided details on which configuration was appropriate for both the number one and number two doors for all 757s, and how to inspect for the correct ones. Boeing received feedback from four operators, including FedEx, and two of those found incorrect configurations of latch assemblies.
NTSB Safety Recommendations
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. We recommend that Boeing review and update their aircraft maintenance manuals (AMMs) and illustrated parts catalogs (IPCs) for the 727, 737, and 757 model airplanes to ensure they depict the correct configuration for the bannis latch. We recommend that, after completing the updates to their AMM and IPCs, Boeing issue a service bulletin advising operators of affected 727, 737, and 757 model airplanes to inspect and, if necessary, modify or replace their bannis latches with the correct configuration.
 
We recommended that the FAA require all operators of Boeing 757 airplanes to inspect the bannis latches on their airplane doors and modify or replace them, if necessary, so they comply with the correct configuration. We also recommended that the FAA require operators of Boeing 727 and 737 model airplanes that use the same bannis latch design to also inspect and modify or replace their bannis latches. We recommend that the FAA require these operators to update their AMM in accordance with the revised Boeing AMM and IPCs. FLIGHT RECORDERSThe event aircraft was manufactured in 1988 and was operating such that it was required to be equipped with a CVR that records a minimum of the last 2 hours of aircraft operation, and was required to be equipped with a flight data recorder (FDR) that recorded, at a minimum, 22 parameters, as cited in 14 CFR Part 121.344(c).

Solid State Flight Data Recorder (SSFDR)

The Honeywell Solid State Flight Data Recorder (SSFDR) records airplane flight information in a digital format using solid-state flash memory as the recording medium. The SSFDR can receive data in the ARINC 573/717/747 configurations and can record a minimum of 25 hours of flight data. It is configured to record 256 12-bit words of digital information every second. For more detailed information, see the Flight Data Recorder - Specialist’s Factual Report located in the docket.

The data indicated that the aircraft departed CHA at about 2224 EDT. About 5 seconds after takeoff, the data indicate the crew moved the landing gear lever handle to the up position. About 22 seconds later, at 2224:09, the indicated quantity of hydraulic fluid in the left hydraulic system and the left hydraulic system pressure started to decrease. A left hydraulic system low quantity indication and master caution were recorded shortly thereafter. The aircraft leveled off at about 4,800 ft mean sea level, turned back toward CHA, and performed two passes over the airport at a low altitude. The aircraft then maneuvered for a final approach to runway 20 at CHA. On final approach, the landing gear lever indicated down; however, data indicate the landing gear was not in the down and locked position. Acceleration data indicate the aircraft landed on runway 20 with the landing gear not extended at about 2347. An engine 1 and engine 2 fire warning indicated shortly after landing. The recording ended at 2347:37.

Cockpit Voice Recorder (CVR)

The model CVR installed on the aircraft, a Honeywell HFR5-V, records a minimum of 120 minutes of digital audio stored on solid state memory modules. Four channels are recorded: one channel for each flight crew, one channel for a cockpit observer, and one channel for the cockpit area microphone. Upon arrival at the laboratory, it was evident that the CVR had not sustained any heat or structural damage, and the audio information was extracted from the recorder normally, without difficulty.