ATL94GA148

The pilot stated that he had just completed dispensing a load of chemical used to control mosquito's. while on a reposition flight to dispense another load of chemical, the aircraft engine stopped producing power. An emergency autorotation was accomplished into a wooded area. The aircraft came to rest in the top of a tall oak tree. The pilot exited the aircraft through the windshield and managed to climb down out of the tree. The pilot estimated that he had approximately 25 gallons of fuel on board the aircraft at the time of the accident. Examination of the aircraft engine revealed that there was continuity of the engine drive chain, and the cylinder compression was within acceptable limits. The aircraft spark plugs were black and sooted. There was fuel in the lines and in the aircraft fuel injector. The aircraft fuel injector was damaged in the accident, and could not be tested for operation.

History of flight

On July 30, 1994, at 1500 eastern daylight time, a Hughes TH55-A, N789MC was substantially damaged following a collision with a tree during an emergency landing attempt near Savannah, Georgia. The commercial pilot received minor injuries in the accident. The aircraft was being operated under the provisions of 14 CFR Part 91 by the Chatham County Mosquito Control. Visual meteorological conditions existed at the time, and no flight plan had been filed for the aerial application flight.

The pilot stated that during a repositioning flight to dispense mosquito control chemicals, the aircraft engine stopped producing power. He attempted an emergency landing in a wooded swamp area. The aircraft came to rest in the top of a large oak tree.

Personnel information

The pilot held a commercial pilot certificate, with airplane single and multiengine, helicopter, and instrument airplane and helicopter ratings. He had a current second class medical at the time of the accident.

The pilot had accumulated approximately 300 hours of flight experience in the Hughes TH55-A helicopter.

Additional personnel information may be obtained in this report on page 3 under section titled Pilot Information.

Aircraft information

The Hughes TH55-A helicopter is a two place utility helicopter. The aircraft was originally designed as a training aircraft for military operations. This aircraft had been purchased from the military and modified with spray equipment, for the purpose of dispensing chemicals to control mosquitos.

Additional aircraft information may be obtained in this report on page 2 under section titled Aircraft Information.

Meteorological information

Meteorological information may be obtained in this report on page 3 under section titled Weather Information.

Wreckage and impact information

The aircraft came to rest in the top of a tall oak tree. All three main rotor blades showed signs of chordwise compression buckling along the leading edges. The tail boom was separated from the fuselage at the attach point. The right side of the fuselage had extensive impact damage, and the cockpit canopy was fractured and separated from the aircraft. The aircraft fuel tank was intact, and had approximately ten gallons of fuel remaining in the tank.

All transmission belts were in place, and showed no signs of excessive wear. The electric clutch engagement solenoid was checked, and operation was normal. The electric fuel pump was tested and found to operate normally.

There was continuity of the aircraft controls from the cyclic and collective through the swash plate and into the main rotor head. All fractures of the tail rotor cables were consistent with tensile overload failure.

Examination of the aircraft engine revealed that the aircraft fuel injector had been damaged during the impact, and operational testing of the unit was not possible. The unit was disassembled, and an inspection of the diaphragm revealed that the rubber diaphragm was pliable, and there were no holes in the diaphragm.

There was continuity of the engine drive train, and the compression of the cylinders was within the normal limits. The aircraft timing was checked, and the timing was set in accordance with the maintenance manual requirements. An examination of the aircraft spark plugs revealed that the plugs were dark black in color, and had heavy carbon sooting.

Additional information

This investigation was conducted at the request of the Chatham County Mosquito Control. The aircraft had been removed from the accident site, and was in the Chatham County Mosquito Control Hangar at the time of the examination.