NTSB Factual Report

On December 7, 2015, at 1230 central standard time, a McDonnell Douglas Helicopter 600N, N607BP, impacted terrain following a loss of control during landing near Angleton, Texas. The private pilot and passenger sustained minor injuries, and the helicopter sustained substantial damage. The helicopter was registered to and operated by the Military Museum of Texas, Houston, Texas, as a 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed at the time of the accident, and no flight plan was filed. The helicopter departed a private helipad near Houston, Texas, at 1150.

According to the pilot, after he arrived near the intended landing location, he conducted an area reconnaissance about 300 to 500 feet above ground level (agl), and noted the winds were calm. After the approach, the pilot was hovering about 15 feet agl, when the helicopter pitched nose down, and the pilot pulled aft on the cyclic to recover. The helicopter then rolled to the right, and the pilot applied left cyclic to recover. The pilot stated the helicopter seemed to right itself in a wobble when the helicopter "snap turned" to the right and entered a severe spin. The pilot then attempted to land the spinning helicopter. During the landing, the helicopter impacted terrain and rolled onto its left side. The helicopter engine was still operating after the pilot and passenger exited the helicopter. A small grass fire ignited near the engine exhaust and was extinguished with a fire extinguisher.

A witness reported the helicopter performed a flyover of the area and a 360-degree turn to land. The helicopter flew over some trees about 150 feet agl, and the helicopter pitched forward in an extreme nose down attitude. The nose pitched back and the helicopter entered a spin. The helicopter then impacted terrain and rolled over.

The 52-year old pilot held a private pilot certificate with a helicopter rating. The pilot reported he had accumulated 300 total flight hours and 210 flight hours in the make/model of the accident helicopter. He received some training in the helicopter from local pilots, but had not received any flight training from the manufacturer. The pilot's most recent flight review was completed on March 3, 2015, in a Robinson R44 helicopter.

The helicopter was recovered to the Military Museum of Texas and was examined on December 9th, by representatives of MD Helicopters, under the supervision of the Federal Aviation Administration (FAA). The airframe exhibited crush damage to the left side, and the tail boom remained partially attached to the airframe. The main rotor blades were bent opposite the direction of rotation, the blade skins were warped and wrinkled, and the trailing edges were separated. Blade tip weights were missing from several blades. Main drive system continuity was established from the main transmission and rotor head, and through the NOTAR (no tail rotor) fan. The NOTAR fan blades exhibited rotation damage to the plastic blade body, the fan housing was deformed and exhibited rotational scoring consistent with blade tip contact. Flight control continuity was established to the cyclic, collective, and anti-torque control systems. The lateral cyclic bellcrank was fractured and retained for further examination. The anti-torque pedals torque tube was fractured and retained for further examination. Examination of the bellcrank and torque tube fracture surfaces revealed the fractures were consistent with overload failure.

The Rolls-Royce 250-C47M engine was examined on December 29-30th, by a representative of Rolls-Royce, under the supervision of the FAA. The engine remained within the engine bay and attached to the airframe. The engine, engine bay, and lower aft fuselage section exhibited areas of scorching and blackening from a post-impact fire. The gas producer (N1) drive train was rotationally free and continuous from the starter generator pad to the compressor impeller during manual rotation. The power turbine (N2) drive train could not be manually rotated due to stage four turbine wheel damage which was consistent with the accident sequence. Visual examination of the compressor inlet guide vanes and impeller blades revealed no anomalies or evidence of foreign object damage. Visual examination of the stage four power turbine wheel through the exhaust collector support revealed it shifted radially off center of its normal operating position when visually compared to the tunnel housing. The blade shroud of the stage four wheel was absent. One blade was fractured about mid-span with the balance of the blades displaying impact damage. The exhaust collector support displayed two extruded openings on the right forward side consistent with the fractured stage four blades. The upper and lower magnetic chip detectors were removed and void of any material. Both the engine oil filter and Combined Engine Filter Assembly (CEFA) oil filter bypass buttons remained in their normal positions.

Both the engine incident recorder (IR) and maintenance terminal data were extracted from the electronic control unit (ECU). No hard faults were recorded within the ECU IR prior to the initiation of the accident sequence. The initial triggering fault of a torque exceedance was recorded and was consistent with the rotor blades contacting the ground.

The postaccident examinations of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operations.

The helicopter was registered to the Military Museum of Texas on September 16, 2011. According to the operator, the most recent annual inspection was completed on April 11, 2015, at a total airframe time of 3,948.6 hours. The engine had accumulated 3,680 total hours. The airframe and engine logbooks were not available during the investigation.

NTSB Probable Cause

A loss of control while hovering for reasons that could not be determined, because postaccident examination revealed no mechanical anomalies or failures that would have precluded normal operation.