Incident Overview
On October 23, 2014, at approximately 1400 central daylight time, a Bell UH-1H helicopter (registration N72595) experienced an in-flight separation of its left sliding cabin door near San Isidro, Texas. The door subsequently impacted one of the main rotor blades, causing substantial damage to the helicopter. The three crew members aboard were not injured.
Flight Details
The helicopter was registered to the U.S. Department of Homeland Security and operated by U.S. Customs and Border Protection under 14 Code of Federal Regulations Part 91 as a public use flight. Visual meteorological conditions prevailed, and the flight was not operated on a flight plan. The flight originated from Brooks County Airport (BKS) in Falfurrias, Texas, at about 1345, with its intended destination being McAllen Miller International Airport (MFE) in McAllen, Texas, after completing a routine law enforcement patrol.
Earlier that day, the crew had departed MFE at approximately 1100 for a routine law enforcement patrol lasting about 2 hours 15 minutes, which concluded without incident. During that patrol, the pilot and co-pilot doors, as well as the main cabin quarter doors, were removed. The sliding main cabin doors were secured in the fully open position.
Preflight Inspection
After landing at BKS to refuel and eat lunch, the crew conducted a preflight inspection. During this inspection, the co-pilot and a tactical team member (TTM) examined the left side of the helicopter and noted that the open door latch pin was missing from the left sliding door latch. The TTM reportedly discussed the missing pin with the co-pilot. According to the TTM, the co-pilot advised that the pin was not required to be installed. The co-pilot stated that he had informed the pilot about the missing pin but was uncertain if the pilot fully understood him.
In-Flight Event
About 15 minutes after departing BKS, during cruise flight, the crew heard a loud bang, and the pilot felt a momentary upset in the helicopter's flight path. The helicopter performed normally after the event, but the pilot decided to make a precautionary landing in an open field. During the post-flight inspection, the crew discovered that the left sliding cabin door had departed the aircraft. The door was later found separated into two pieces approximately 1 mile northeast of the landing site. One main rotor blade sustained substantial damage consistent with an in-flight impact with the door assembly.
Postaccident Examination
A postaccident examination did not reveal any anomalies consistent with a failure of the door assembly or airframe structure that would have caused the separation. The retaining angle remained attached to the door and appeared undeformed. The door latch pin had separated from its lanyard and was found lying on the aft cabin floor. The exact reason the pin had separated from the lanyard before the accident flight could not be determined.
The helicopter operating handbook permitted flight up to 120 knots with the door properly secured in the open position. To properly secure the door, it must be in the full open position with the door latch pin installed. In the event the door inadvertently opened in flight, the airspeed was to be reduced below 50 knots to allow the door to be closed. If the door could not be closed, it had to be fully opened and secured by the open door latch.