SOMERSET, PA, USA
N162AK
Elves ROTORWAY EXEC 90
The homebuilt, experimental helicopter was on approach to an off airport landing area, when the pilot realized that he could not change the throttle setting. The helicopter touched down hard, and one skid collapsed. The collective/throttle assembly was removed. When heated, the throttle became difficult to move. Testing by the kit manufacturer obtained similar results. The bushings that restricted the throttle movement were supplied by the kit manufacturer.
On May 5, 1996, about 1700 eastern daylight time, a homebuilt Rotorway, Exec 90, helicopter, N162AK, was substantially damaged while landing in Somerset, Pennsylvania. The Airline Transport rated pilot was not injured. Visual meteorological conditions prevailed, and no flight plan had been filed for the local, personal transportation flight which originated at Blairstown, Pennsylvania, about 1620, and was operated under 14 CFR Part 91. In the NTSB Accident Report, the pilot stated: "...Throttle stuck on approach to landing at Horizon Outlet Mall...Inadequate power in stuck position resulted in hard landing and roll over." An FAA Airworthiness Inspector stated: "...The pilot...stated he thought the heat build-up aft of the cabin caused the nylon bushings in the collective throttle system to stick. The collective and throttle system were removed from the aircraft for test...placed the assembly in an oven and heated it to 150 degrees. The temperature would be approximate to the heat in the engine compartment area. It required both hands to move the twist grip a fraction of an inch after heated...The bushings in question will require additional clearance for the throttle rod...." Additional testing was conducted by the manufacturer using bushings with 0.002 and 0.005 clearance. The testing revealed that with the 0.002 inch clearance bushing and a temperature of 200 degrees F, "...was very hard to turn and would be very difficult to change throttle settings...." Additionally, they noted: "...For production the throttle shaft bushing tolerance are made to have a minimum of .005 inch and a maximum of .009 inch based on the throttle shaft being .375 inch diameter...." In a telephone interview, FAA Airworthiness Inspector, Patrick Shippert, reported that the bushings were supplied by the kit manufacturer.
the kit manufacturer's inadequate design of a throttle bushing, which resulted in insufficient clearance after the bushing became heated, restricted throttle movement, lack of engine response, hard landing, gear (skid) collapse, and rollover.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
