LAX05TA156 · Sikorsky S-70A

The left auxiliary power unit (APU) door departed the helicopter in flight and contacted the main rotor blades. The pilot made precautionary landing. The APU door is located on the top of the helicopter, near the main rotor blades, and it is secured using two upper and lower, push-pin type snap latches. Following the accident, the latches were located separately in a field; each latch remained secured to portions of the door material. The APU door is opened and secured by maintenance daily and its security was verified by the pilot during the preflight. Post accident examination of the two fractured sections of left APU door with latches and the two hinge keepers showed that the hinge keepers failed as a result of fatigue fractures and allowed the door to separate in flight. Review of the manufacturer's process specifications disclosed that the failed hinge keepers were manufactured by a now superceded production process. This superceded production process introduced contamination, which resulted in fatigue of the hinge keepers. A new hinge was designed and implemented over 2 years prior to the accident; however, there was no recall by the helicopter manufacturer to replace the older design. In the United States, two civilian operators use this helicopter (five helicopters total) and the primary operator is the United States military. The United States military has classified this as a low-risk issue. Due to the damage sustained to the parts, the manufacturer was unable to confirm that the problem would have been detectable by flight crew or maintenance personnel prior to the accident flight using the current inspection methods.

Verbatim NTSB analysis and probable cause from the NTSB dataset