FAIRBANKS, AK, USA
N700WA
Beech 18
During landing on the gravel airstrip, as the pilot placed the propellers into reverse, the airplane began to veer left. He applied right brake and continued to apply more reverse on the right engine. He was unable to control the airplane, and the airplane departed the left side of the airstrip and encountered brush and rough terrain. Examination of the engines revealed that a pin in the right engine propeller control unit, on which the propeller control cam slides, separated. The cockpit propeller control operates the control cam directly. Examination of the fracture surface of the pin disclosed that the pin failed in overload.
On July 6, 1996, at 1000 Alaska daylight time, a retractable gear, wheel equipped Beech 18 Volpar airplane, N700WA, registered to Kalitta flying Service of Lakeview, Oregon, and operated by F.S. Air Service of Anchorage, Alaska, ran off the left side of the runway during the landing roll at Van Curler's mining airstrip, located 60 miles from the Fairbanks VOR on the 050 degree radial. The air taxi flight, operating under 14 CFR Part 135, departed Anchorage and the destination was the mining airstrip. A company visual rules flight plan was in effect and visual meteorological conditions prevailed. The certificated airline transport pilot and the four passengers were not injured. The airplane received substantial damage. During a telephone conversation with the pilot on July 9, 1996, he stated he landed on the runway using an airspeed of 90 to 100 knots. As soon as the main wheels touched down he applied reverse thrust. The airplane began to veer left and he applied more reverse thrust on the right engine and applied more right brake. The airplane continued to veer left and departed the left side of the runway approximately 1,200 feet beyond the touchdown point. As the airplane departed the left side of the runway, the pilot stated he applied power to the left engine but could not tell if the engine responded because the airplane entered the brush and rough terrain. The airplane's main and nose landing gear collapsed rearward after striking the brush and rough terrain. The engines were removed and shipped to Dominion Propeller in Anchorage, Alaska. The right engine's propeller was disassembled and no mechanical problems were found. The propeller control linkages on the left and right engine were exercised. The left engine's propeller control would move into the feather detent. The right engine's propeller control would stop moving prior to going into the feather detent. The "Beta" tube, the tube that the propeller control collar slides along to port and unport oil to the propeller hub, was removed from the front of the engine and a small piece of metal was seen protruding from one of the oil ports. The piece of metal could not be retrieved from the "Beta" tube. The right engine's propeller control unit was removed and disassembled at F.S. Air Service's maintenance facility in Anchorage, Alaska. Inside the control unit, the propeller pitch control pin was found separated from the pitch control arm/collar. The separated pin was not found inside the propeller control unit. The propeller control unit has only one exit point for the oil circulating through the unit. The opening was large enough to allow the separated pin to pass through. The exit point opens into the engine's nose gear case. The separated pin was not located. The function of the pin was to allow a cam to slide along the pin and position the propeller pitch control collar at various points along the "Beta" tube, thereby controlling the propeller's pitch. With the pin separated, the cam would not be able to move the pitch control collar as designed to control the propeller's pitch. The propeller pitch control unit was submitted by F.S. Air Service to Allied Signal Aerospace, the manufacturer of the airplane's engines, for metallurgical examination. The fracture surface was found to be consistent with bending overload fracture. The material was examined and found to be manufactured with the proper alloy.
The malfunction of the propeller control unit on the right engine.
Source: NTSB Aviation Accident Database
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