Topeka, KS, USA
N402PD
Robinson R44
During a routine night surveillance flight, the helicopter's pilot heard the single reciprocating engine "fluctuate" slightly; he noted that the engine's rpm gauge was above the "normal operating limits", and the gauge [needle] was "jumping up-and-down". In order to keep the engine within operating limits, the pilot disabled the engine governor and decreased the engine rpm. During the return to base, the pilot heard the engine rev up and the low rotor rpm alarm. During the precautionary landing in a parking lot, the helicopter's main rotor blade contacted a light pole. The helicopter subsequently made a hard landing, coming to rest on its side. The magneto, governor controller, clutch actuator, engine/rotor tachometer and drive-belts were removed for examination. The governor, clutch actuator, tachometer, and drive belts all passed either a visual or electronic test inspection. A visual inspection of the magneto revealed that the exterior of the magneto was absent any damage, but was lightly covered with an "oil like" liquid. The magneto was bench tested and produced regular sparks beginning at 196 rpm's. The magneto’s signals to the governor box were clear and equal, with only a very slight overlap between both signals. The magneto was disassembled; the light oil like substance was present on the inside of the magneto. The inspection also revealed "whiskers" of residue/corrosion on the magneto contacts; which were black instead of the normal silver color. During the test it was noted that the magneto should have produced a regular spark at 150 rpm, and that the residue/corrosion could send extra impulse signals to the governor box; producing an indication that the engine is revving. However, it was also noted that because there was only a slight overlap of the electrical signals, and since the magneto passed the other test items,a malfunction could not be duplicated.
On April 5, 2008, about 0003 central daylight time, a single-engine Robinson R44 helicopter, N402PD, was substantially damaged after impacting a light pole during a precautionary landing in a parking lot near Topeka, Kansas. The commercial pilot and two observers were not injured. The helicopter was registered and operated by the Topeka Kansas Police Department. Night visual meteorological conditions prevailed for the Public Use flight. The pilot reported that during a routine surveillance flight, he heard the helicopter's engine "fluctuate" slightly; he then looked at the engine gauge and saw that the engine rpm gauge was above the "normal operating limits", and the gauge [needle] was "jumping up-and-down." In order to keep the engine within operating limits, the pilot disabled the engine governor and decreased the engine rpm. The pilot also reported that as they started to return to base, they heard the engine "rev up" followed by the low rotor rpm alarm. The pilot executed an autorotation, after the rotor rpm recovered and entered the normal operating range; the pilot decided that they would perform a precautionary landing. A parking lot security camera caught the night image of the helicopter's landing. The video shows the parking lot and helicopter lights. As the helicopter approaches the parking lot, a spark/light shower is displayed as the helicopter's main rotor blade contacts a light pole. The helicopter subsequently makes a hard landing, coming to rest on its side. The helicopter was recovered for examination. An initial examination by a Federal Aviation Administration (FAA)Inspector, failed to identify any pre-impact abnormalities with the helicopter. The magneto, governor controller, clutch actuator, engine/rotor tachometer and drive-belts were removed and shipped to the helicopter manufacturer for further examination. On May 21, 2008, the NTSB, technical representatives from the airframe manufacturer, and the Operator inspected the components at the Robinson Helicopter factory. The governor, clutch actuator, tachometer, and drive belts all passed either a visual or electronic test inspection. A visual inspection of the magneto revealed that the exterior of the magneto was absent any damage, but was lightly covered with an "oil-like" liquid. The magneto was bench tested and produced regular sparks beginning at 196 rpm’s. The magneto's signals to the governor box were clear and equal, with only a very slight overlap between both signals. The magneto was disassembled; the light oil-like substance was present on the inside of the magneto. The inspection also revealed "whiskers" (residue/corrosion) on the magneto contacts; which were black instead of the normal silver color. The technical representative noted that the magneto should have produced a regular spark at 150 rpm, and that the residue/corrosion could send extra impulse signals to the governor box; producing an indication that the engine is revving. He also noted that because there was only a slight overlap of the electrical signals and since the magneto passed the other test items; it could not be determined whether or not the over-speed/revving condition was caused by the magneto. A review of the engine maintence record reveals that the 100-hour inspection was completed on April 3, 2008. The logbook entry noted that during the inspection, the magnetos were "checked and timed."
A malfunctioning magneto, resulting in a high engine rpm and low rotor warning indications. A contributing factor was the impact with a light pole, during the precautionary landing.
Source: NTSB Aviation Accident Database
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