Incident Overview
On April 5, 2008, at approximately 0003 central daylight time, a single-engine Robinson R44 helicopter, registration N402PD, was substantially damaged during a precautionary landing in a parking lot near Topeka, Kansas. The helicopter, operated by the Topeka Kansas Police Department, was engaged in a routine surveillance flight. The commercial pilot and two observers were not injured. Night visual meteorological conditions prevailed for the Public Use flight.
Pilot Report
The pilot reported that during the flight, he heard the engine "fluctuate" slightly. Observing the engine gauges, he noted that the engine rpm gauge was above the normal operating limits and that the needle was "jumping up-and-down." To keep the engine within limits, the pilot disabled the engine governor and decreased the engine rpm. As they began 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, he decided to perform a precautionary landing.
Video Evidence
A security camera in the parking lot captured the landing. The video shows the parking lot and helicopter lights. As the helicopter approaches, a spark or light shower is visible as the main rotor blade contacts a light pole. The helicopter then made a hard landing, coming to rest on its side.
Post-Accident Examination
The helicopter was recovered for examination. An initial inspection by a Federal Aviation Administration (FAA) inspector did not identify any pre-impact abnormalities. The magneto, governor controller, clutch actuator, engine/rotor tachometer, and drive belts were removed and sent to the manufacturer for further analysis.
On May 21, 2008, the National Transportation Safety Board (NTSB), along with 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 visual or electronic testing. A visual inspection of the magneto revealed no exterior damage, but it was lightly covered with an "oil-like" liquid. Bench testing showed that the magneto produced regular sparks beginning at 196 rpm, with clear and equal signals to the governor box, though there was a very slight overlap between both signals. Disassembly revealed the oil-like substance inside the magneto, as well as "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, potentially indicating that the engine was revving. However, because the electrical signals had only a slight overlap and the magneto passed other tests, it could not be determined whether the over-speed/revving condition was caused by the magneto.
Maintenance Records
A review of the engine maintenance records showed that a 100-hour inspection was completed on April 3, 2008. The logbook entry noted that during the inspection, the magnetos were "checked and timed."