N420M

HISTORY OF FLIGHTOn August 3, 2017, at 1503 Pacific daylight time, an experimental, amateur-built Lancair IV-TP, N420M, was substantially damaged when it was involved in an accident near Rio Linda, California. The commercial pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

An onboard GPS and avionics unit captured data from the accident flight; the airplane departed Auburn Municipal Airport (AUN), Auburn, California, about 1455. The pilot established the airplane on a heading of about 195° toward the destination of San Carlos, California and began to climb. The pilot contacted air traffic control and requested visual flight rules flight following to the destination, and when the controller advised the pilot that the airplane had been identified on radar, the pilot did not respond. The controller then saw the airplane turn and descend toward McClellan Airfield (MCC), Sacramento, California; no further communications were received from the accident pilot. (See Figure 1).

Figure 1: Flight Track Showing Diversion

Data showed that, at 1459:17, the fuel pressure began to rise from about 40 pounds per square inch (psi) to 43 psi. A few seconds later, after reaching 6,492 ft mean sea level (msl), the airplane pitched down and banked to the left, reaching 25° nose down and 36° left wing down. At 1459:24, torque and N1 (gas generator speed) were at 64% and 95%, respectively, and 15 seconds later, began to decrease consistent with the engine producing idle power. During that time, the oil pressure dropped from about 31 to 15 psi and fuel flow was reduced from 46 to 16 gallons per hour; the interstage turbine temperature decreased from 1,118°F to 786°F.

At 1459:53, the oil pressure increased to 28 psi and the voltage began to slowly decrease from 28 volts, consistent with the generator turning off and the airplane being powered by the standby alternator. The N1 stabilized about 65%, and the engine torque dropped to about 8%. At 1501:41, N1 began to decrease again and reached 0 about 15 seconds later, with a simultaneous decrease in oil pressure and ITT. At 1502:00, the aircraft banked about 40° to the left, aligning with runway 16 at MCC.

During the last 38 seconds of the flight, the airplane lost about 425 ft of altitude while slowing from 125 knots (kts) to 89 kts. During this time, the engine torque and N1 were 0, while the propeller rpm consistently slowed from 1,746 to 948. The next data point, 1 second later, depicted the airspeed as 0, and several parameters showed discontinuities consistent with impact.

Witnesses saw the airplane flying south along 28th Street toward MCC at low altitude. The airplane then made a sharp turn to the right and disappeared into the trees.

After the accident, the pilot's family listened to the radio transmissions for the final portion of the flight and they stated that they heard the pilot make three radio transmissions, the second of which was not discernable aside from the airplane's registration number. The third transmission was (presumably) the pilot acknowledging a controller's directions to squawk a discrete code by pressing the microphone; the pilot did not report an emergency or convey that he was in distress. PERSONNEL INFORMATIONThe pilot's personal flight records were not recovered. On his last application for a medical certificate, the pilot reported 7,000 total hours of flight experience. AIRCRAFT INFORMATIONThe Lancair IV-TP was an experimental, amateur-built airplane constructed mainly of composite materials The pilot purchased the kit directly from Lancair International Inc., in November 1995. The airplane received a special airworthiness certificate in the experimental category in September 2004. The logbook entry on August 4, 2016, stated that "a list of discrepancies and unairworthy items" were provided to the airplane's owner. This list, and the mechanic who performed the inspection, could not be located after the accident. The pilot recorded that he replaced the starter/generator in July 2016 at a total time of 868.0 hours.

Engine and Propeller

The Diemech M601D engine is a two-spool engine comprising a gas generator that drives a power turbine, which drives a reduction gearbox. The gas generator compressor consists of two axial flow stages and one centrifugal stage. Inlet air enters the compressor section radially just forward of the accessory section and travels forward through the compressor. The exiting compressor air enters an annular combustor to mix with fuel for the combustion process. The gas generator turbine nozzles then direct the expanded flowpath gases to the gas generator turbine, which directs the exiting gases to the power turbine for the final power extraction before exiting the engine forward of the compressor inlet.

The power turbine drives the propeller system by means of the reduction gearbox. The accessory gearbox, which is located on the aft end of the engine drives all engine accessories by a direct shaft coming from the compressor spool. Typical engine accessories are the main fuel pump, fuel control unit, starter/generator, hydraulic pump, and the propeller governor, which is driven by the reduction gearbox located at the front of the engine.

The oil system is a circulatory pressure system with an integral oil tank incorporated into the accessory gearbox. This system provides lubrication for all areas of the engine and oil pressure for the torque meter and propeller pitch control.

The powerplant was controlled by three sets of levers. The power lever controlled the power output of the engine and the propeller blade angles in Beta and reverse. The propeller lever controlled the propeller speed via the primary propeller governor and emergency propeller feathering. The condition lever actuated the fuel shutoff valve and, if an emergency circuit was on, controlled engine power.

The propeller was equipped with an overspeed governor on the cylinder front face, which featured an internal spring-loaded weighted valve. Centrifugal forces of the propeller rpm act on the weighted valve, and once the spring pressure is overcome, the valve opens, allowing oil from the low pitch area in the hub to the drain until the rpm decreases to correspond with speed setting.

The airplane was not equipped with an emergency electric propeller feather pump; thus, emergency feathering could be activated by moving the propeller lever onto the feather stop. However, this required the gas generator portion of the engine to still be operating, since the gas generator drove the main oil pump and provided oil pressure to the propeller for pitch control and emergency feathering. However, when an engine loses power for any reason, the gas generator section quickly stops rotating and there is no engine oil pressure available to feather the propeller. With no engine power to turn the propeller, it will quickly stop rotating, making the counterweights and aerodynamic pressure on the rotating blades the only driving force available to feather the propeller. Unless the pilot immediately moves the propeller conditioning lever into the feather stop when the engine loses power, the propeller will effectively be locked at the blade pitch that was selected at the time of the engine failure.

Fuel System

The airplane was last fueled on July 29. According to the refueling technician, the pilot requested that the airplane be refueled to capacity, and the records indicated he purchased 103 gallons of Jet A. The technician recalled filling both of the wing tanks; he noted that the pilot rarely filled the belly tank. Onboard data indicated that the right and left fuel tanks each contained about 20 gallons of fuel before the flight, but the total amount of fuel onboard was unknown.

The fuel system comprised two 56-gallon wing tanks and a 36-gallon belly tank; all tanks fed into a 24-gallon header tank. From the header tank via an electric boost pump, the fuel passed through a filter and continued by the fuel pressure sensor and then the fuel flow sensor to the fuel control unit (FCU). The fuel pressure and flow rate displayed on the instrument panel were based on what the pressure header tank supplied to the FCU. The header tank was equipped with a vent line.

The airplane was equipped with a VR Avionics Fuel System Management (FSM), which was designed to automatically select the fuel tank with the lowest quantity as the feeder tank. In an effort to equalize the fuel level, the tank would be switched to the lowest when an imbalance of 3 gallons was reached. The system additionally monitored the fuel pumps and fuel pressure, providing the pilot with an annunciation if the levels were low. AIRPORT INFORMATIONThe Lancair IV-TP was an experimental, amateur-built airplane constructed mainly of composite materials The pilot purchased the kit directly from Lancair International Inc., in November 1995. The airplane received a special airworthiness certificate in the experimental category in September 2004. The logbook entry on August 4, 2016, stated that "a list of discrepancies and unairworthy items" were provided to the airplane's owner. This list, and the mechanic who performed the inspection, could not be located after the accident. The pilot recorded that he replaced the starter/generator in July 2016 at a total time of 868.0 hours.

Engine and Propeller

The Diemech M601D engine is a two-spool engine comprising a gas generator that drives a power turbine, which drives a reduction gearbox. The gas generator compressor consists of two axial flow stages and one centrifugal stage. Inlet air enters the compressor section radially just forward of the accessory section and travels forward through the compressor. The exiting compressor air enters an annular combustor to mix with fuel for the combustion process. The gas generator turbine nozzles then direct the expanded flowpath gases to the gas generator turb...