Accident Overview
On December 7, 2015, at 1230 central standard time, a McDonnell Douglas Helicopter 600N, registration N607BP, impacted terrain following a loss of control during landing near Angleton, Texas. 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, and no flight plan was filed. The helicopter had departed a private helipad near Houston, Texas, at 1150.
Pilot and Witness Accounts
According to the pilot, after arriving near the intended landing location, he conducted an area reconnaissance at about 300 to 500 feet above ground level (agl) and noted calm winds. After the approach, while hovering about 15 feet agl, the helicopter pitched nose down. The pilot pulled aft on the cyclic to recover. The helicopter then rolled to the right, and the pilot applied left cyclic. The pilot stated that the helicopter seemed to right itself in a wobble when it "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 engine was still operating after the pilot and passenger exited. A small grass fire ignited near the engine exhaust and was extinguished with a fire extinguisher.
A witness reported that the helicopter performed a flyover and a 360-degree turn to land. The helicopter flew over some trees at about 150 feet agl, then pitched forward in an extreme nose-down attitude. The nose pitched back, and the helicopter entered a spin. It then impacted terrain and rolled over.
Pilot Information
The 52-year-old pilot held a private pilot certificate with a helicopter rating. He reported 300 total flight hours, with 210 hours in the accident make and model. He received some training from local pilots but none from the manufacturer. His most recent flight review was completed on March 3, 2015, in a Robinson R44 helicopter.
Aircraft and Examination
The helicopter, a McDonnell Douglas Helicopter 600N (NOTAR design), was recovered to the Military Museum of Texas and examined on December 9, 2015, by representatives of MD Helicopters under FAA supervision. The airframe showed crush damage to the left side, and the tail boom remained partially attached. Main rotor blades were bent opposite the direction of rotation, with warped and wrinkled skins and separated trailing edges. Blade tip weights were missing from several blades. Main drive system continuity was established from the main transmission and rotor head through the NOTAR fan. The NOTAR fan blades exhibited rotation damage, and the fan housing was deformed with 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 and the anti-torque pedals torque tube were fractured and retained for examination; fracture surfaces were consistent with overload failure.
Engine and Systems Examination
The Rolls-Royce 250-C47M engine was examined on December 29–30 by a Rolls-Royce representative under FAA supervision. The engine remained in the bay attached to the airframe. Areas of scorching and blackening from a post-impact fire were noted. The gas producer (N1) drive train was rotationally free and continuous during manual rotation. The power turbine (N2) drive train could not be manually rotated due to stage four turbine wheel damage consistent with the accident sequence. No anomalies or foreign object damage were found in the compressor. The stage four power turbine wheel had shifted radially off center; its blade shroud was absent, one blade was fractured mid-span, and others showed impact damage. The exhaust collector support had two extruded openings consistent with fractured stage four blades. Magnetic chip detectors were void of material. Both engine oil filter and Combined Engine Filter Assembly oil filter bypass buttons were in normal positions.
Data from the electronic control unit's incident recorder and maintenance terminal showed no hard faults recorded prior to the accident sequence. The initial triggering fault was a torque exceedance consistent with rotor blades contacting the ground.
Postaccident examinations of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operations.