WPR16FA126

The failure of the left engine due to water contamination and the pilot's subsequent failure to maintain single-engine minimum control airspeed, which resulted in an uncontrolled descent. Contributing to the accident was the pilot's lack of total and recent flight experience in the accident airplane make and model, which reduced his capacity to manage an inflight loss of power.

After multiple taxi tests of the twin-engine airplane, the airline transport pilot departed on a local personal flight. About 70 minutes later, the airplane was about 10.5 nautical miles southeast of the airport, and the pilot requested a landing clearance. Witnesses heard one of the airplane's engines "backfiring" as the airplane proceeded northwest towards the airport, and the pilot reported to an air traffic controller that he was having trouble with his left engine and could not maintain altitude. The pilot told the controller that he was going to land in a field next to a railroad track, and the airplane then turned about 45° to the left. A witness about 1/2 mile from the accident site saw the airplane in a wings-level descent for a few seconds before it suddenly rolled into a steep left bank. Security cameras showed the airplane descending with a rapidly increasing left bank angle until it impacted a building, and a postcrash fire erupted. Postaccident examination of the airplane revealed that the left engine's propeller was feathered, and the left engine-driven fuel pump and carburetor contained trace amounts of water and displayed a white powdery residue, consistent with long term exposure to water contamination. The left wing's inboard and outboard fuel tank caps displayed rust around their circumferences, and the caps did not form a seal when inserted into the fueling portholes, which indicated that both fuel tanks were susceptible to contamination from rain water. Examination of the right engine showed that all four intake camlobes were worn nearly concentric in shape, and the corresponding tappet faces displayed spalling. Worn camlobes can lead to a degradation in engine performance. The failure of the left wing's fuel cap seals, evidence of water contamination in the fuel system, and the feathered left engine indicate that it is likely the pilot feathered the left engine in response to a power loss resulting from water contamination. Although a witness reported heavy rainfall in the winter that preceded the accident at the airport where the airplane was based, the investigation could not determine when or how water was introduced into the fuel system. The high speed taxi tests conducted by the pilot before the accident flight suggest he may have been aware of a problem with the airplane before departure, but the reason he conducted the taxi tests is unknown. According to the pilot's logbook, since purchasing the airplane about 10 months before the accident, he had accumulated about 19 hours of flight time in the airplane of which 1.4 hours were in the 90 days preceding the accident. Additionally, the majority of his recent flight experience involved single-engine airplanes, thus the pilot's lack of total and recent experience in the airplane make and model suggest that he may not have been prepared to manage an inflight loss of power in a twin-engine airplane. Factoring in the reported 11-knot surface wind, radar data indicated that the airplane's airspeed dropped below the airplane's minimum control airspeed with an engine inoperative (Vmc) after it turned into the inoperative engine near the end of the flight and remained there for the remainder of the descent. Therefore, it is likely that the airspeed decayed to the point where the pilot was unable to counteract the asymmetrical thrust produced by the right engine, which led to the rapid left roll seen in the security camera images, further loss of altitude, and impact with the building.

The pilot held an airline transport certificate with ratings for airplane multi-engine land and a flight instructor certificate for airplane single-engine land. He held a first-class medical certificate issued on January 13, 2016, at which time he reported 2,161 total flight hours. The medical certificate included one restriction: "must have available glasses for near vision." According to the pilot's logbook, he had accumulated about 19 hours of total flight time in the accident airplane of which 1.4 hours were in the 90 days preceding the accident. His first flight in the accident airplane took place in August 2015 when he ferried the airplane to California. After the ferry flight, the pilot accrued a total of about 27 additional flight hours in other airplanes and performing flight instruction. The flight instructor who administered the pilot's most recent flight review reported that the flight review was conducted in March 2015 in the pilot's BE60 airplane and included two simulated left engine failures. The first simulated engine failure took place during an instrument landing system approach, and the pilot completed the engine out procedure and continued the approach successfully. The instructor noted that, during the simulated engine failure, the pilot's yaw control was "good" and that the airplane's descent was "smooth and right on." A subsequent simulated engine failure took place at 5,000 ft when the flight instructor reduced the left engine manifold pressure to 13 inches. He then asked the pilot to complete a 45° turn and hold his altitude, but the airplane was unable to maintain altitude due to the combination of a low power setting and a higher-than-standard rate turn. During both simulated engine failures, the pilot successfully kept the airspeed above the airplane's minimum controllable airspeed (Vmc). According to FAA records, the airplane was manufactured in 1955 and registered to the pilot on September 2, 2015. The airplane was powered by two Lycoming O-320-A, normally-aspirated, direct-drive, air-cooled, 150-horsepower engines. The pilot's family furnished the original aircraft logbooks, which included service information from May 1986 to July 2015. A review of the logbooks revealed that the airplane's most recent 100-hour inspection was completed on July 15, 2015, at which time the left engine tachometer read 4,051 flight hours, and the right engine tachometer read 4,059 flight hours. According to the logbooks, at the time of the most recent 100-hour inspection, the left and right engines had accumulated about 1,955 hours and 1,957 hours, respectively, since their most recent major overhauls. Records of the left and right engine overhauls could not be located in the available aircraft records, and the dates of the overhauls could not be determined. The airplane total time at the time of the accident was estimated using the right engine tachometer time as the airplane's recording hour meter was not recovered. Based on the pilot's approximate 19 hours of accumulated time in the airplane make and model, the airplane's total time at the time of the accident was estimated to be about 4,077 hours. Records furnished by a fixed base operator at HWD indicated that the pilot had purchased fuel from their self-service facility 11 times in the previous 10 months. The records showed that the pilot did not purchase fuel at HWD on the day of the accident; they showed that he last purchased fuel for the airplane at HWD in September 2015. The pilot's logbook showed that he flew the airplane to Nut Tree Airport (VCB), Vacaville, California on May 1, 2016. VCB refueling records indicated that the pilot purchased about 15 gallons of 100LL gasoline that day. Before that, the pilot had purchased about 28 gallons of 100LL gasoline at VCB on September 27, 2015. A procedure to feather the propeller of an inoperative engine was included in the airplane's aeronautical flight manual (AFM). According to the AFM, the procedure included the following steps: Throttle "CLOSED". Prop Control "FEATHERED". PROP CANNOT BE FEATHERED UNDER 700 RPM. Mixture control "IDLE CUT-OFF". Ignition switches "OFF". Electric fuel pump (if in use) "OFF". Main valve "OFF". The manufacturer's published Vmc for the airplane is 85 mph. METEOROLOGICAL INFORMATION The 1152 recorded weather observation at HWD included wind 280° true at 11 knots, visibility 10 statute miles, clear skies, temperature 27°C, dew point 8°C, and an altimeter setting of 30.06 inches of mercury. According to an employee of a fixed base operator at HWD, the airport received significant levels of rain during the winter of 2016 that resulted in an overflow of the airport's drainage ditch. However, the investigation was unable to determine whether the airplane was parked outside during the winter of 2016. WRECKAGE AND IMPACT INFORMATION Initial examination of the accident site by the National Transportation Safety Board investigator-in-charge revealed that the airplane came to rest at the base of a fiberglass railroad car wash building, about 5 nm southeast of HWD. All major structural components of the airplane were accounted for at the accident site, which was contained within an area about 35 ft long and 25 ft wide. The fuselage came to rest inverted on a heading of 095° magnetic and was destroyed by fire. With the exception of some thermal damage, the empennage was intact and remained connected to the fuselage by the airplane's rudder control cables. The right wing was destroyed by fire, and its corresponding engine was inverted and covered in soot. The left wing was co-located with the main wreckage in a near vertical position, at rest against the southeastern end of the building, and exhibited an odor of fuel near the left wingtip. Both sets of propeller blades remained attached to their respective hubs; the left engine propeller blades were in the feathered position and did not display any damage. The right engine propeller blades were in a low pitch position and displayed nicks, gouges, and tip curling. Left aileron control continuity was confirmed from the left aileron bell crank to the wing root where the cables had been cut by recovery personnel. The rubber seal to the inboard left tank fuel cap was rusted, and the cap did not form a seal inside the fuel tank ring when installed. The fuel cap rubber seal to the left outboard tank displayed some corrosion and did not form a seal when installed in the fuel tank ring. The left fuel selector valve displayed 3/4 inches of space between the lever and the valve. According to the manufacturer, this position was consistent with an auxiliary tank setting. A trace amount of fuel was drained from the left engine gascolator into a plastic container that had been cleaned and dried. The fuel odor and appearance resembled 100LL aviation grade gasoline; however, a SAR-GEL fuel purity test indicated that the fuel was contaminated with water. The left electric fuel boost pump was not recovered. The right wing aileron bell crank was damaged by fire but remained intact and attached to the primary aileron and balance cables. The right aileron cable was continuous from the bell crank to the chain, which had fracture signatures consistent with overload separation. The right electric fuel boost pump was disassembled, and the gasket and internal components displayed carbon coloring consistent with exposure to fire. The pump was void of fuel, and the fuel screen was found free of debris. One arm from the control T-bar assembly separated at the T-section, and the assembly was damaged by fire; however, the remaining three sprockets were intact. A portion of elevator control tube remained attached to the tube stem. Continuity of the rudder assembly was traced from the rudder torque tube through