FTW99TA046

In dark night conditions, the pilot reported a loss of power at 1000 feet AGL while maneuvering during a routine police flight. During the ensuing emergency descent (autorotation), the pilot maneuvered around a grain elevator and power lines. Just as the pilot pulled on the collective to arrest the rate of descent, a utility pole came into sight at his 12 o'clock position. The main rotor blades struck the pole and the helicopter impacted the ground on its right side. Post-accident examination included an engine run to manufacturer's specifications with the engine in its as removed configuration on the test stand. The tachometer generators were bench tested and the airframe was examined. It was noted that the fuel pump exhibited some leakage, both during the engine test run and a subsequent bench test, however, the engine operated throughout its normal RPM range. No definitive anomalies were revealed that would have contributed to the accident.

On December 7, 1998, at 0028 central standard time, a Bell OH-58A helicopter, N900PD, owned and operated by the Little Rock, Arkansas, Police Department, was substantially damaged during a forced landing (autorotation) following a loss of power, while maneuvering in the vicinity of North Little Rock, Arkansas. Both occupants, the commercial pilot and a police observer (non-pilot crewmember), were not injured. Dark night visual meteorological conditions prevailed and a company VFR flight plan was filed for the 14 Code of Federal Regulations Part 91 public use flight. The routine police aerial observation flight departed the North Little Rock Airport at 2345.

The pilot reported that while he was maneuvering at 1,000 feet AGL and 100 knots, both he and his observer noticed the RPM console light "flicker, stay off, then remained on." Subsequently, he "felt" the aircraft "drop." After initiating an autorotation, the pilot checked the dual tachometer, which indicated a decrease in engine RPM. The pilot then looked for a place to land but could not see the ground due to the weather and dark night. He then checked the instruments and noticed that the N1 was "dropping." As the helicopter neared the ground, the pilot maneuvered to avoid a grain elevator and power lines. Just as he pulled up on the collective to arrest the rate of descent, a utility pole came into sight at the "12 o'clock position", and the main rotors struck the pole as the aircraft settled to the ground. The helicopter rolled over to the right after striking the pole. The non-pilot crew member stated that he "pulled the emergency fuel shut off, and turned the battery switch to off to prevent fire."

Initial examination of the wreckage at the accident site by an FAA airworthiness Inspector, revealed that the main rotor system and the tailboom were structurally damaged and the skid assembly was separated from the aircraft. Also, a burn mark was found in the grass adjacent to the left engine exhaust. The fuel quantity indicator indicated 340 pounds of fuel on board. The fuel cell was intact and removal of the fuel filter revealed no visually detectable contaminates. After the initial inspection, the wreckage was transported to Mid-South Aviation, located at North Little Rock Airport, for further examination. The examination revealed the following:

A portion of the tail rotor drive shaft, just aft of the oil cooler, exhibited rotational scoring around the circumference of the shaft. The main rotor mast was fractured near the top and some torsion twisting was noted. Both interior and exterior cowling of the engine compartment were undamaged, except for some minor damage on the forward portion of the firewall adjacent to the short shaft. The short shaft was separated at the couplings on both ends, and rotational scoring was present at the center of the shaft. Rotational scoring was present on the tail rotor drive shaft adjacent to the burner drain plug line, which exhibited corresponding rub marks. The fuel tank was visually checked to be approximately half full, and no evidence of fuel leakage was found in the engine compartment. All fuel, lube and pneumatic coupling bead nuts were checked finger tight. Both gas producer (N1) and power producer (N2) turbine wheels rotated freely. The fuel control was rigged properly and appeared to be functional. Caution lights functioned when power was applied and the audio warning system was checked to be functional. The throttle body was found in the cutoff position, and the governor pointer was at mid-range. At the conclusion of this examination, the engine, with accessories attached in their original configuration, was removed and shipped to Dallas Airmotive, Dallas, Texas on January 20, 1999. More detailed examination and testing of the engine and accessories at Dallas Airmotive revealed the following:

A pneumatic pressure bench check was conducted. All fittings, connections, and clamps were tight and intact except for one, at the governor. There were some indications of FOD damage on the first stage compressor blades. After visual inspection, the engine was placed on a test stand without alterations. The engine was operated through all normal RPM ranges and performed within manufacturers specifications. In addition to the engine examination, both tachometer generators were bench tested with no anomalies noted. All of the fuel system components were found undamaged and operational except for the fuel pump. During the engine test run, the fuel pump exhibited some leakage. After the engine run, the fuel pump was removed from the engine, bench tested, and some leakage was noted.

Manufactured in 1972, the helicopter, serial number 71-20855, was maintained on the manufacturer's 100 hour inspection program. On the day of the accident, the operator reported that the aircraft had 39.9 flight hours since its last 100 hour inspection, completed on November 10, 1998. According to entries in the maintenance records, the aircraft was in compliance with all applicable Airworthiness Directives, and no pre-accident entries showed outstanding maintenance discrepancies or uncorrected defects.

The Allison T63-A-720 model engine (S/N AE 405457) was previously overhauled equipment installed by the U.S. Army on June 9, 1994. There were four routine engine inspections completed prior to the accident.