JETMORE, KS, USA
N88007
Schweizer 269C
The pilot said he was going to practice an auto rotation. He said he '...rolled the throttle back to idle position and dropped the collective...[and]noted a red light on the dash and could hear the engine had quit running.' He said the subsequent auto rotation '...terminated in a hard landing.' The on-scene investigation revealed flight and powerplant control operational continuity and fuel in the accident helicopter's fuel tanks. The engine was test run and its low idle was 1,300 rpm. According to a representative from a company that maintains and rebuilds helicopters like that of the accident helicopter, '...it is possible for an engine to die when a rapid roll-off of [the] throttle is accomplished and too low an idle RPM setting exists.' The FAA Approved Flight Manual said that the pilot should 'Split the needles by lowering the collective while maintaining throttle setting. The throttle correlation will establish a high idle RPM (approximately 2500 RPM) and will prevent the engine from loading up or stalling on recovery.'
On July 27, 1999, at 1730 central daylight time (cdt), a Schweizer 269C, N88007, piloted by a private pilot, was substantially damaged when it collided with the ground during a pilot described practice auto rotation. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 personal flight was not operating on a flight plan. The pilot reported no injuries. The flight departed Hayes, Kansas, at 1645 cdt. The pilot said he "...climbed [the helicopter] to between 3500 and 3600 feet, turned the helicopter straight west into the wind and rolled the throttle back to idle position and dropped the collective. Immediately upon doing so, I noted a red light on the dash and could hear the engine had quit running. When I looked at the engine RPMs, I could see it was at zero." The pilot said the auto rotation "...terminated in a hard landing." According to the Federal Aviation Administration Principal Maintenance Inspector (PMI) who spoke with the pilot, N88007's pilot told him that he performs auto rotations with engine operating at 2,000 rpm. The PMI said the pilot stated the engine stopped running at the 2,000 rpm indication. The PMI reported continuity and operation to the factory limits was established for the flight and powerplant controls. The engine was started and its lowest idle rpm was 1,300. The magnetos check revealed the rpm drop was within the manufacturer's specifications. The PMI said a blue colored liquid, similar to 100LL AVGAS was found in N88007's fuel tanks. The pilot said he departed Hayes, Kansas, with full fuel, 49 gallons, and had flown about 30 minutes before the engine stopped running. The pilot said he had filled N88007's fuel tanks at Hayes, Kansas. A representative from a company who maintains and rebuilds helicopters and has experience with the accident helicopter's type said, "...it is possible for an engine to die when a rapid roll off of [the] throttle is accomplished and too low an idle RPM setting exists." According to the FAA Approved Flight Manual (AFM), the section entitled, "Practice Autorotations," the pilot is to "Split the needles by lowering the collective while maintaining throttle setting. The throttle correlation will establish a high idle RPM (approximately 2500 RPM) and will prevent the engine from loading up or stalling on recovery." An excerpt from the AFM addressing this procedure is appended to this report.
The pilot's use of improper procedures by not following the helicopter manufacturer's recommended engine RPM reduction procedures during autorotations. A factor was the pilot not attaining the proper rotor RPM during the autorotation practice.
Source: NTSB Aviation Accident Database
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