History of Flight
On May 1, 2019, about 0935 mountain standard time, a Beech S35 airplane, N6864Q, was substantially damaged during an accident at Sedona Airport (SEZ), Sedona, Arizona. The pilot and flight instructor were not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as an instructional flight.
The pilot had recently purchased the airplane, which had been flown from Deer Valley Airport (DVT) to SEZ for a pre-buy inspection about one week prior. That flight was uneventful, and the inspection revealed no anomalies. The accident flight was the first since the purchase, intended to familiarize and qualify the pilot under insurance and FAA experience requirements.
Both pilots reported that the preflight, engine start, taxi, and runup were normal. They planned to depart from runway 21 for airwork and return. The engine was leaned for takeoff. After liftoff, both pilots sensed a significant loss of engine power, the stall warning sounded, and the airplane began to roll right wing down. They pushed the nose down. Due to the right roll and a left crosswind, the airplane drifted right, impacting the unpaved surface alongside the runway. It traversed rough terrain and slid to a stop on its belly near the intersection of runway 21 and taxiway A8. The landing gear collapsed, and the left wing sustained substantial damage.
Aircraft Information
The airplane had a total time in service of about 5,906 hours. The engine had about 877 hours since major overhaul, and the most recent annual inspection was completed in August 2018.
Wreckage and Impact Information
Primary damage included the outboard left wing, lower nose area, and all three landing gear with their supporting structure. Two of three propeller blades were damaged; one was loose in the hub, the other intact. The engine appeared undamaged aside from minor intake damage. Initial examination at the recovery facility revealed no pre-impact mechanical deficiencies that would have precluded continued operation.
Engine test runs were conducted after replacing the damaged propeller and plumbing a fuel supply. Fuel was observed leaking from both sides of the fuel control unit (FCU) where throttle and mixture control shafts exited. The engine ran normally but was shut down due to fuel leaks. Three components were sent to the engine manufacturer (Continental) for testing: the throttle and metering assembly (T/MA), fuel manifold valve assembly, and engine-driven fuel pump.
The T/MA, original to the engine and 14 years old, had not been overhauled despite a recommended 12-year/1,700-hour overhaul interval. It showed accumulated grime around shaft exits, consistent with long-term fuel leakage, and evidence of prior fuel staining on the airframe. Manual rotation of the mixture control shaft revealed a variation in resistance, like a partial dead band. Bench testing confirmed leakage like that observed in the field; the T/MA failed 4 of 7 test points. Disassembly revealed shaft-sealing O-rings that were non-resilient due to aging. The fuel manifold valve assembly and engine-driven fuel pump tested normally.
Additional Information
The previous owner stated he typically flew from high-elevation airports in the morning and did not recall ever leaning for takeoff, though on high-temperature days he would lean after reaching full rich power on the runway. The CFI on the accident flight reported adjusting the mixture for best operation considering density altitude. The pilot recalled leaning to roughness then enriching, but did not recall how far the mixture was backed out.