Accident Overview
On September 30, 2018, at 1735 eastern daylight time, a Robinson R44 II helicopter, registration N440SH, operated by Charm City Helicopters, was substantially damaged during a loss of control on the ground following a precautionary landing atop the Longwell Parking Garage Structure in Westminster, Maryland. The commercial pilot was not injured, and there were no ground injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the flight to reposition the helicopter atop the parking garage. The flight was conducted under 14 CFR Part 91.
The operator provided 4- to 5-minute helicopter rides as one of the attractions at the Westminster Fallfest, using the top deck of the multi-story parking garage as a helipad. At the completion of each flight, passengers were off-loaded, the next group was loaded while the helicopter ran, and the helicopter departed over the down-sloping portion of the top deck.
Pilot Account
The pilot stated that the helicopter experienced an engine and main-rotor overspeed at takeoff, and he performed a precautionary landing at the bottom of the parking deck that sloped downward immediately in front of him. After disembarking the passengers, he attempted to reposition the helicopter to its original spot. He increased the throttle to return to normal engine rpm, and the aircraft started spinning uncontrollably. As the helicopter rotated around its mast, the owner/operator standing beside the helicopter ducked to avoid the tailboom before it struck a parked automobile. The pilot stopped the engine and rotation by pulling the mixture control.
In subsequent interviews, the pilot's account of the flight remained unchanged, but the events after landing differed. He insisted he was misunderstood and intended to stop the engine after deplaning passengers and reposition by attaching ground-handling wheels. According to the pilot, the engine was idling with throttle at idle stop when it accelerated un-commanded, the helicopter rotated, and rotation could only be stopped by pulling the mixture control. In another account, he reported that after deplaning, he needed to accelerate the engine to 70 percent for cooldown, and when he increased the throttle, the engine accelerated uncontrolled, the helicopter rotated, struck a parked car, and came to rest only after he pulled the mixture control.
The operator reported hearing something "heighten in pitch" as the helicopter departed, and that loud whining occurred again when the helicopter began to spin on the ground after landing and deplaning passengers.
Pilot Information
The pilot held commercial pilot and flight instructor certificates with ratings for rotorcraft helicopter, and a private pilot certificate for airplane single engine land. He did not possess an instrument rating. His most recent FAA second-class medical certificate was issued on May 7, 2018. He estimated 700 total flight hours, with 400 in rotorcraft and 200 in the accident helicopter make and model.
Aircraft Information
The helicopter was manufactured in 2005 and had accrued 2,216.8 total aircraft hours. The most recent annual inspection was completed December 1, 2017, concurrent with a complete airframe and engine overhaul. The engine and helicopter had accrued 70 hours since that date. On August 24, 2018, at 2192.1 total aircraft hours, the right magneto was removed and replaced due to "engine rpm fluctuating."
Weather and Wreckage Examination
The 1750 weather observation at Frederick Municipal Airport, 20 miles west, included clear skies, calm winds, 10 miles visibility, temperature 24°C, dew point 15°C, altimeter 30.30 inches of mercury.
Wreckage examination on October 1, 2018, showed all major components attached. The tailrotor blades were substantially damaged but attached. The bottom of the vertical stabilizer displayed substantial damage, and the tailboom had a small dent. The main and tail rotors rotated smoothly by hand. Control continuity was established. Overlapping rotational skid marks matching the R44 landing gear were observed on the parking deck. The down-sloping ramp was 190 ft long with a 10 ft 6 inch elevation change at a slope of 5.5 percent.
Detailed Examination and Test Run
A detailed examination and test run on October 9, 2018, found the engine started immediately and idled smoothly at 68%. The rpm governor was turned on, and the engine accelerated until the governor captured control at 80%. Engine rpm then increased, paused twice at intermediate thresholds, then accelerated through normal operating range past 105%, slowed slightly, and surged between 96% and 104% un-commanded. The governor was turned off, and the engine operated smoothly at 100%. When the governor was turned back on, the engine rpm surged again. The governor operated as designed below 80%.
The governor was controlled by a governor controller module receiving a signal from the right-side engine magneto. Inspection of the magneto revealed tachometer leads in close proximity to the points cam and its attachment screw, with damaged wire insulation and exposed strands.
A video and photos of the magneto disassembly were reviewed by a Technical Investigator from Robinson Helicopter Company. According to the investigator and the magneto service manual, the tachometer leads were not properly routed and were in close proximity to the rotating cam screw head. The tachometer points also displayed contamination and misalignment. The report stated, "The damage to the wire insulation will allow contact between the wire and rotating screw head creating an intermittent short to ground. This will send an errant signal to the governor control unit which in turn will manipulate the throttle accordingly."