THOMASTOWN, MS, USA
N32PH
Bell 47G-3B1
The pilot stated he was pulling up the aerial spray rigged helicopter from the platform of the 'nurse truck' in order to reposition for a better placement on the platform, when he experienced uncommanded rotation. His ground crew stated, as he pulled up, a piece of the aircraft flew off and the tail rotor began to spin down. The aircraft went into an uncontrollable rotation, and the main rotor blades collided with an adjacent small tree stand. The helicopter impacted the terrain, the right landing skid collapsed, and the helicopter rolled over on its right side. Subsequent examination of the wreckage and interviews of the pilot, passenger, and ground crew revealed the approach and pull up for the second approach were into downwind conditions. The piece of the aircraft that flew off was a section of the tail rotor drive shaft. Except for the missing piece of shaft, no mechanical abnormalities could be found in the pilot controls, engine, or drive train.
On April 19, 1999, about 0730 central daylight time, a Bell 47-G3B, N32PH, registered to Provine Helicopter Service, Inc., operating as a 14 CFR Part 137 aerial application flight, crashed while attempting a liftoff from a truck mounted platform near Thomastown, Mississippi. Visual meteorological conditions prevailed and no flight plan was filed. The helicopter sustained substantial damage and the commercially-rated pilot and a passenger reported no injuries. The flight originated about 30 minutes before the accident. The pilot stated he departed with the land owner for an orientation flight over the tract to be sprayed. Upon completion of the orientation flight, he returned to the "nurse truck" and made an approach to deplane the land owner. He was not content with his landing skid placement on the platform and pulled up for a second approach, when the helicopter started an uncommanded yaw, followed by an uncontrolled rotation. He stated he thought the passenger had stepped on the right anti-torque pedal. He maneuvered the helicopter away from the truck, but the main rotor blades collided with a small tree, the right landing skid hit the terrain hard enough to collapse, and the aircraft came to rest on its right side. According to the two-man ground crew, as the helicopter was lifting off the platform for better positioning on the platform, they heard a "loud bang similar to a shotgun blast". They saw a piece of the aircraft fly away and the tail rotor stopped turning. The helicopter performed multiple rotations, tilted toward its right side, and impacted a stand of small trees with its main rotor blades. The helicopter came to rest on its right side within the trees. Subsequent examination of the accident site and interview of the pilot, ground crew, and land owner by Federal Aviation Administration (FAA) inspectors, revealed that the pilot was making a downwind approach to the platform in order to position the passenger near the ladder to expedite his exit off the platform. The wreckage revealed the throttle was fully open and the right anti-torque pedal was full forward. A 16-inch section of tail rotor drive shaft located in the plane of the main rotor tips was missing and the tail boom truss had sustained a main rotor blade strike. One of the main rotor blade tips (outer 4-6 inches) had witness marks that would be consistent with striking the tail rotor shaft. Except for the aforementioned, the inspectors could find no mechanical malfunctions of the pilot's flight or engine controls, the engine or its components, or the transmission or drive train to the main or tail rotor systems. The FAA operations inspector stated, "It appears that the pilot through cyclic and collective control input caused the rotor blades to make contact with the tailboom and tailrotor drive shaft".
An in-flight loss of control caused by the main rotor severing the tail rotor drive shaft as a result of the pilot's cyclic pull-up into a tailwind for his second approach and landing. The loss of the tail rotor caused an uncontrollable descent and tree strike with the main rotor and in-flight collision with terrain. Contributing to the accident was the pilot's improper decision to make a downwind approach and landing.
Source: NTSB Aviation Accident Database
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