What happened
On October 4, 2011, at approximately 12:50 central daylight time, a Eurocopter EC120B, registration N3925A, sustained substantial damage during a landing in an unprepared grass field located roughly ten miles east of McAllen Miller International Airport (MFE) in McAllen, Texas. The flight was being conducted under 14 CFR Part 91 for the Department of Homeland Security to provide aerial support for a border patrol mission.
Upon realizing the mission would be delayed, the pilot decided to perform a no-hover landing in an unfamiliar field to conserve fuel. During the approach, the pilot realized the aircraft had too much forward speed for a no-hover landing and transitioned to a slow, running landing to avoid brown-out conditions. The helicopter touched down at a speed between 16 and 24 knots and slid forward approximately 34 feet. Following this, the aircraft experienced a forward pitching moment, causing the main rotor blades and the wire strike protection system to strike the ground. The helicopter then rotated counter-clockwise and came to rest on its right side, which resulted in the tail boom being severed. The skids and main rotor blades also sustained damage. The pilot and the supplemental aircrew member sustained 2 minor injuries and were not killed.
The investigation
The investigation reviewed the operator's aircraft standardization manual (ASM), which specifies that during a running landing, the pilot should decelerate using aft cyclic to approximately five degrees nose up while slightly lowering the collective to maintain a constant approach angle. The manual requires the pilot to arrive at an airspeed slightly above effective translational lift and a height of ten feet above the ground simultaneously. Furthermore, the pilot must hold the collective stationary after ground contact to prevent rapid pitch reductions.
The pilot reported that there were no mechanical issues with the aircraft prior to the event. During the landing, the pilot applied full aft cyclic but could not recall his actions regarding the collective control.