History of Flight
On November 16, 2008, at 0028 Central Standard Time, a Bell OH-58C helicopter, registration N153GF, sustained substantial damage when it landed hard in a field near Quitman, Arkansas. The commercial rated pilot was not injured; the passenger was fatally injured. The helicopter was registered to and operated by the Arkansas Game and Fish Commission. No flight plan was filed, and night visual meteorological conditions prevailed for the Public Use flight conducted under 14 Code of Federal Regulations Part 91. The flight originated from Heber Springs Municipal Airport (HBR) in Heber Springs, Arkansas, at 1130.
The purpose of the night surveillance flight was to support ground personnel in apprehending individuals engaged in illegal night-time deer hunting, known as "spot-lighters." The pilot was wearing night vision goggles (NVGs) while operating over a large open field at approximately 150 feet above ground level (agl) on a westerly heading at 10 knots. The pilot reported suddenly noticing a master caution, low rotor lights, a low rotor audio, and a sinking of the aircraft. After glancing inside, he observed a decaying N2/Rotor tachometer reading. He immediately lowered the collective and landed straight down.
Meteorological Information
Weather reported at Adams Field Airport (LIT) in Little Rock, Arkansas, at 0053, included wind from 250 degrees at 8 knots, visibility 10 statute miles, clear skies, temperature 01°C, dew point 03°C, and a barometric pressure of 30.32 inches of Mercury.
Personnel Information
The 29-year-old pilot held a commercial pilot certificate for airplane single and multi-engine land and instrument airplane, as well as a commercial pilot certificate for rotorcraft-helicopter and instrument helicopter, issued on March 31, 2008. His last FAA first-class medical certificate, with no limitations, was issued on January 10, 2008.
The pilot reported 3,602 total hours in all aircraft, including 1,727 hours in helicopters. He had 332 total hours in the OH-58C, of which 270 hours were as pilot-in-command. In the preceding 90 days, he flew 159 hours in helicopters, with 39 hours in the OH-58C. In the last 30 days, he flew 66 hours in helicopters, including 30 hours in the OH-58C.
The pilot also accumulated 1,005 total hours at night, with 765 hours as pilot-in-command and 96 hours in the OH-58C. In the last 90 days, he flew 73 hours at night, and 21 hours in the last 30 days.
According to the FAA, the pilot flew for the Arkansas Air National Guard and had signed a contract with the Arkansas Game and Fish Commission to assist during deer season, which began two weeks before the accident. He reported a total of 3,500 flight hours, with 300 hours in the same make and model as the accident helicopter.
Wreckage and Impact Information
Examination of the accident site revealed that the helicopter impacted the ground in a nose-low, left bank attitude. The helicopter remained upright; the tail boom was deflected downward and partially separated from the airframe forward of the horizontal fins. The left front side of the cockpit exhibited impact damage from contact with the main rotor blades.
The helicopter was recovered to a salvage facility for examination. Inspection of the airframe and fuel system revealed no mechanical deficiencies. Flight control continuity was established for all major flight controls to the cockpit.
The Gas Producer (N1) and Power Turbine (N2) tachometer generators were removed from the accessory gearbox with electrical leads attached and tested by spinning with a hand drill. Movement was noted in both N1 and N2 tachometers. The rotor tachometer, mounted on the rotor transmission, sustained damage during impact and could not be tested.
The engine was removed from the airframe and sent to Premier Turbines in Neosho, Missouri, where it was examined and test-run under FAA supervision on December 18, 2008. According to the Rolls Royce Final Engine Investigation Report, the engine was installed in a turnover stand for receiving inspection. Magnetic chip detector plugs were clean, and a pressurized pneumatic leak check detected no leaks. The primary and secondary orifices of the fuel nozzle were debris-free, and the air shroud contained a normal amount of carbon accumulation. Approximately 250 cc of oil was drained from the accessory gearbox, appearing normal in color and consistency. A borescope inspection of the first and third stage turbine areas found no impact damage or anomalies.
Impact damage was noted on the event compressor, which was removed for disassembly inspection. The engine was prepared to run on a calibrated test stand with a "slave" compressor provided by Premier Turbines. During the test, an oil leak was observed near the #6 and #7 oil sump can, which exhibited external impact damage from the accident. Due to the leak, an abbreviated test run was conducted. Despite this, the engine met power requirements for max continuous and take-off (intermediate) power. The specific compressor efficiency of the slave unit was unknown, but the unit was serviceable and had been used to test overhauled modules.
The event compressor was disassembled and examined. The compressor front support was buckled inward from the 12 o'clock to 4 o'clock position. The compressor scroll was dented at the left elbow location, consistent with an external crushing force. All compressor and stator airfoils were intact, with some impact damage on the first stage rotor blades. Tip rub was noted on the first, second, fifth, and sixth stage vanes, with corresponding witness marks on the compressor rotor seals. Rotational witness marks were observed on the compressor impeller blade leading edges, impeller shroud, rear face of the impeller, and forward portion of the compressor rear support. These signatures were consistent with the compressor rotating at the time of impact.
The engine examination and limited test-run on a Rolls Royce approved test stand using a slave compressor did not reveal any deficiencies that would have prevented the engine from producing power at the time of the accident.
Additional Information
According to the OH-58 Flight Training Guide, the procedure for an engine failure during a hover is to autorotate. Section 4-50 describes the steady-state autorotation, which requires rotor RPM within limits, correct airspeed, normal descent rate, and positioning to terminate in the intended landing area. The guide notes that at night or with NVGs, attitude control is critical due to reduced visual references, and pilots should attain a steady-state autorotation before descending through 200 feet agl.