History of Flight
On May 30, 2018, at 1108 Pacific daylight time, a Beech A36 airplane, N191HL, made a hard landing on a highway near Tonopah, Nevada, following a loss of engine power during the enroute climb to cruise. The private pilot and passenger sustained minor injuries, and the airplane sustained substantial damage. The airplane was registered to and operated by the pilot as a personal flight under Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight departed Tonopah Airport at 1048, destined for Dodge City Regional Airport, Kansas.
According to the pilot, during preflight he checked the engine oil, which indicated 12 quarts. The departure was uneventful. After reaching about 8,000 ft mean sea level, he smelled smoke and heard a popping sound. The engine began losing power, and he initiated a return to the airport. During descent, the engine lost all power, and the pilot maneuvered to land on a highway. The landing approach was obscured by obstacles including power distribution cables, and the airplane landed hard on the highway median. Substantial damage occurred to the lower fuselage and both wings.
Personnel Information
The pilot held a private pilot certificate with a single-engine land rating, issued in October 2015. He reported 225 total flight hours, with 99 hours in the accident make and model. According to FAA records, he purchased the airplane about 10 months before the accident.
Aircraft Information
The airplane was equipped with a six-cylinder Continental IO-520-BB engine. In December 2013, it was fitted with a Western Skyways turbo-normalizing system per Supplemental Type Certificate SA8676SW. The FAA-approved flight manual supplement required the fuel mixture to be set to "FULL RICH" from engine start to cruise climb; adjustments were permitted only after leveling off in cruise. The supplement specified cruise climb fuel flow between 26.5 and 28.5 gph up to the critical altitude (approximately 18,000 ft pressure altitude).
Engine Examination
Post-accident examination revealed all fuel and oil lines intact. Five holes were found in the crankcase, and the airplane belly was covered in oil. In the cabin, throttle and propeller controls were full forward, mixture about 1 inch aft of full rich, cowl flaps open, and auxiliary fuel pump OFF (the supplement required LO above 10,000 ft and HIGH for priming). The engine was shipped to Continental Motors for examination. The fuel pump, metering unit, and manifold valve were tested; though none met production standards, they pumped, metered, and flowed fuel appropriately, with fuel pressure and flows above nominal. Fuel flowed equally from each injection line, and injectors were clear.
Disassembly revealed oil starvation and catastrophic failure. Piston rods for cylinders 3, 4, 5, and 6 had broken from the crankshaft; all tappets seized in their sleeves; camshaft showed thermal discoloration. The number 4 piston crown had melted down to the compression ring land with a blackened, frosted appearance, and a channel from the crown to the piston pin exposed and damaged the oil scraper ring. Other piston crowns and cylinder head combustion surfaces had a sand-blasted, peened appearance with minimal deposits. Continental Motors representatives stated this damage was consistent with pre-ignition and detonation.
Engine Monitor Data
The airplane was equipped with a G3 Graphic Engine Monitor. Data from an earlier flight showed fuel flow about 5 gph after start, manifold pressure 13 inHg, CHT averaging 250°F. During takeoff and climb, fuel flow increased to about 33 gph, manifold pressure 29 inHg, RPM 2,730, CHT ~340°F, TIT ~1,200°F. Fuel flow then dropped, and during cruise it was about 14 gph with CHT ~400°F. Oil temperatures varied between 127°F and 166°F.
For the accident flight, similar initial values were observed. During takeoff and climb, manifold pressure reached 30.1 inHg, RPM 2,700, but fuel flow never exceeded 19.4 gph. CHT and TIT climbed, averaging about 530°F and 1,500°F about 4 minutes after takeoff. Three minutes later, CHT for cylinders 4, 5, and 6 began rising; cylinder 4 reached 771°F after another 3 minutes. Over the last 8 minutes, all CHT dropped to about 200°F as data ended. Oil temperatures climbed to 204°F during climb and peaked at 217°F coincident with cylinder 4's highest CHT.
The pilot could not recall the mixture setting during takeoff and climb for the accident flight, but presumed it was likely full rich. He reported the airplane was serviced with 100-low lead aviation gasoline in Tonopah, and they had landed there because his wife (the passenger) was nauseous; she had recovered before departure.