WPR19LA128 · Beech 35 S35

About 1 week before the accident, the previous owner had flown the fuel-injected single-engine airplane about 70 miles for inspection before selling to the accident pilot. That flight was uneventful as was the pre-buy inspection. The sale was accomplished, and the airplane remained at the accident pilot’s airport, which was at an elevation of about 4,800 ft. The accident pilot arranged to begin an airplane checkout process with a certificated flight instructor (CFI), and their flight was to be the first flight since the pre-buy inspection. The CFI and the pilot both reported that the preflight inspection, engine start, taxi out, and engine runup for the planned local flight were all normal. Based on the airport’s high elevation, they leaned the fuel mixture for takeoff.

The takeoff roll and liftoff were normal, but just after the airplane lifted off, both pilots sensed a significant loss of engine power, the stall warning sounded, and the airplane began to roll right-wing down. The airplane drifted to the right and impacted the unpaved surfaces adjacent to the right side of the runway. The airplane traversed some rough terrain, the landing gear collapsed, and the airplane slid to a stop. The left wing sustained substantial damage.

Initial postaccident examination of the airplane did not reveal any pre-impact mechanical deficiencies or failures that would have precluded normal operation. The engine started and operated normally during a test run while it remained on the airframe. However, fuel was observed leaking from the throttle and metering assembly (T/MA), so testing was terminated. Visual inspection of the T/MA and nearby components revealed grime around the shaft-case penetrations and blue staining on the airframe structure below the T/MA. Both were evidence of pre-existing fuel leaks. Although the leak origination date could not be determined, the appearances of both signatures were consistent with their existence while the airplane was in service rather than as a result of the accident impact. The investigation could not determine how long the leak had been occurring or if it was present at the time of the last annual inspection, about 8 months before the accident. The visual evidence of the existing leak was likely not significant enough to have been identified during the pre-buy inspection.

Disassembly of the T/MA revealed that the fuel leaks were a result of O-rings that lacked normal flexibility and were non-resilient. At the time of the accident, the T/MA was 2 years beyond the manufacturer's overhaul schedule of 12 years, which resulted in age-related deterioration of the O-rings, and the consequent fuel leaks.

The fuel leaks in the T/MA had the potential to reduce fuel flow to the fuel manifold valve, resulting in uncommanded and imprecisely controlled leaning of the mixture. The airplane's previous owner reported that he rarely leaned the mixture for takeoff from high-elevation airports whereas the mixture was leaned for the accident takeoff. Thus, the mixture for the previous owner's takeoffs might have actually been unknowingly leaned due to the faulty T/MA but not so much that it prevented takeoff. In contrast, when the accident pilot and CFI leaned the mixture while the engine was at less than full power, the fuel leaks in the T/MA could have caused an overly lean mixture for full throttle operation, resulting in a significant power decrease.

Verbatim NTSB analysis and probable cause from the NTSB dataset