What happened
On October 23, 2014, at approximately 1400 central daylight time, a Bell UH-1H helicopter, registration N725lar, was conducting a law enforcement patrol near San Isidro, Texas. The flight had departed Brooks County Airport (BKS) following a refueling stop. During the cruise phase of flight, the crew heard a loud bang and experienced a momentary upset in the aircraft's flight path. Although the helicopter continued to operate normally, the pilot performed a precautionary landing in an open field.
Following the landing, a post-flight inspection revealed that the left sliding cabin door had separated from the aircraft. The door was later found in two pieces approximately one mile northeast of the landing site. One of the main rotor blades sustained substantial damage consistent with an in-flight impact from the door assembly. The 3 crew members on board were not injured.
During the preflight inspection at BKS, a tactical team member and the co-pilot noted that the door latch pin was missing from the left sliding door latch. The co-pilot reportedly informed the pilot of the missing pin, though there was uncertainty regarding whether the pilot fully understood the communication. The aircraft was being operated with the pilot and co-pilot doors and the main cabin quarter doors removed, with the sliding doors positioned in the fully open position.
The investigation
A post-accident examination of the door assembly and airframe structure showed no anomalies or failures that would have caused the separation. The retaining angle remained attached to the door and showed no deformation. Investigators found that the door latch pin had separated from its lanyard and was located on the aft cabin floor. While the handbook allows flight up to 120 knots with the door in the full open position, it requires the door latch pin to be installed to secure it. The investigation determined that the lack of the door latch pin allowed the door to slide forward during flight, leading to aerodynamic forces separating the door from the sliding track.