N191HLBeech A36 · 1979

On May 30, 2018, at 1108 Pacific daylight time a Beech A36 airplane, N191HL, landed hard 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 Title 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed, and no flight plan had been filed for the cross-country flight. The flight departed Tonopah Airport at 1048, and was destined for Dodge City Regional Airport, Dodge City, Kansas.

The pilot reported that during the preflight inspection he checked the engine oil, and the dipstick indicated an oil level of 12 quarts. The departure was uneventful, and after reaching an altitude of about 8,000 ft mean sea level, he began to smell smoke, and then heard a popping sound. The engine then began to lose power, and he initiated a return to the airport. During the descent the engine lost all power, and the pilot maneuvered the airplane to land on a highway. The pilot stated that the landing approach was obscured by obstacles including a set of power distribution cables, and the airplane landed hard on the highway median.

The airplane sustained substantial damage to the lower fuselage and both wings.

The pilot held a private pilot's certificate with a rating for airplane single-engine land, that was issued in October 2015. He reported a total flight time of 225 hours, with 99 hours in the accident make and model. According to Federal Aviation Administration (FAA) records, he purchased the airplane about 10 months before the accident.

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 in accordance with Supplemental Type Certificate (STC) SA8676SW.

The normal procedures section of the FAA approved flight manual supplement that was included with the STC stated that the fuel mixture should have been set to "FULL RICH" during all operational phases from engine start to cruise climb. Mixture adjustments were then permitted once the airplane had leveled off in cruise flight.

The supplement stated that during cruise climb fuel flow up to the critical altitude (approximately 18,000 ft pressure altitude) should be between 26.5 and 28.5 gph.

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 in accordance with Supplemental Type Certificate (STC) SA8676SW.

The normal procedures section of the FAA approved flight manual supplement that was included with the STC stated that the fuel mixture should have been set to "FULL RICH" during all operational phases from engine start to cruise climb. Mixture adjustments were then permitted once the airplane had leveled off in cruise flight.

The supplement stated that during cruise climb fuel flow up to the critical altitude (approximately 18,000 ft pressure altitude) should be between 26.5 and 28.5 gph.

Engine Examination

Post-accident examination revealed that all fuel lines, oil lines, and ancillary components were intact. Five holes were observed in the engine crankcase, and the entire belly of the airplane was covered in oil. Within the cabin, the throttle and propeller controls were in the full forward position, and the mixture was about 1 inch aft of the full forward (rich) position. Both the cowl flaps, and the cowl flap controls were in the open position, and the auxiliary fuel pump switch was in the "OFF" position (the flight supplement required that it be set to LO at all altitudes above 10,000 and HIGH for engine priming).

The engine was removed and shipped to the facilities of Continental Motors, Inc. for examination under the supervision of an NTSB investigator. A complete engine examination report is contained in the public docket, the following is a summary of findings.

The fuel pump, fuel metering unit, and fuel manifold valve were tested on production test stands in the as-received, field-adjusted conditions. Though none of the units met production test standards, the units were able to pump, meter, and flow fuel appropriately. The fuel pressure and flows on the pump and metering unit were above nominal values throughout all tested ranges. Fuel flowed in equal quantities from each fuel injection line, and the fuel injectors were free of blockage.

Disassembly of the engine case revealed evidence of oil starvation and catastrophic engine failure. The piston rods for cylinders 3, 4, 5, and 6 had all broken away from the crankshaft, and all tappets had seized within their sleeves. The camshaft had evidence of thermal discoloration.

The corners of the number 4 piston crown had melted down to the compression ring land, and the entire crown surface had a blackened and frosted appearance. On one side of the piston, a channel was present from the crown down to the piston pin, exposing and damaging the oil scraper ring.

The crowns of the remaining pistons, along with the cylinder head combustion surfaces had a sand-blasted and peened appearance, with almost no deposit buildups. According to technical representatives from Continental Motors, this damage, along with the damage to the crown of piston number 4, was consistent with the effects of pre-ignition and detonation.

Engine Monitor

The airplane was equipped with a G3 Graphic Engine Monitor, manufactured by Insight Instrument Corporation. The unit was configured to record parameters including fuel flow, manifold pressure, engine RPM, turbine inlet temperature, and both cylinder head and exhaust gas temperatures.

According to the pilot, the flight originated earlier in the day from Haigh Field Airport (O37), Orland, California. Data recovered from the G3 unit revealed that for the first 12 minutes of that flight following engine start, the fuel flow remained at about 5 gallons per hour (gph), the manifold pressure held steady at about 13 inches of mercury (inHg), while the cylinder head temperatures (CHT) climbed to an average of about 250°F. In a manner consistent with takeoff and climb, the fuel pressure, manifold pressure, and engine speed then increased to about 33 gph, 29 inHg, and 2,730 RPM respectively as the CHT's climbed to about 340°F, and the turbine inlet temperature (TIT) reached about 1,200°F. About 8 minutes later, the fuel flow dropped to about 31 gph, and another 7 minutes later, presumably as the airplane entered the enroute cruise phase, the fuel flow dropped to about 14 gph, while the CHT's all equalized at an average of about 400°F. Oil temperatures during the flight varied between 127°F and 166°F.

For the accident flight, similar values were observed during the 8 minutes after engine start. For the takeoff and climb portion, the manifold pressure reached 30.1 inHg, and the engine speed climbed to 2,700 RPM, however the fuel flow never exceeded 19.4 gph. As the flight progressed, the CHT's and TIT began to climb, reaching an average of about 530°F and 1,500°F respectively, about 4 minutes after takeoff. Three minutes later, the CHT for cylinders 4, 5, and 6 began to rise until cylinder 4 reached the highest recorded temperature of 771°F, 3 minutes later. For the last 8 minutes, all CHT's began to drop, reaching about 200°F as the data ended. Oil temperatures climbed to 204°F during the climb phase, and peaked at 217°F coincident with the highest recorded CHT temperature for cylinder 4.

The pilot stated that he could not specifically recall the mixture setting during the takeoff and climb phase of the accident flight, but presumed that because the engine failure occurred during climb, it was likely to have been in the full rich position. He reported that the airplane had been serviced with 100-low lead aviation gasoline while in Tonopah, and that he landed their because his wife, who was the passenger, was becoming nauseous. He stated that she had recovered prior to departing on the accident flight.

The "Transition to Complex" section of the FAA Airplane Flying Handbook (FAA-H-8083-3A) states the following regarding heat management of turbocharged engines:

"High heat is detrimental to piston engine operation. Its cumulative effects can lead to piston, ring, and cylinder head failure, and place thermal stress on other operating components. Excessive cylinder head temperature can lead to detonation, which in turn can cause catastrophic engine failure. Turbocharged engines are especially heat sensitive. The key to turbocharger operation, therefore, is effective heat management.

The pilot monitors the condition of a turbocharged engine with manifold pressure gauge, tachometer, exhaust gas temperature/turbine inlet temperature gauge, and cylinder head temperature. The pilot manages the "heat system" with the throttle, propeller r.p.m., mixture, and cowl flaps. At any given cruise power, the mixture is the most influential control over the exhaust gas/turbine inlet temperature. The throttle regulates total fuel flow, but the mixture governs the fuel to air ratio. The mixture, therefore, controls temperature."