N994PT

On December 25, 2021, about 0825 central standard time, an experimental Lancair IV-TP, N994PT, was substantially damaged when it was involved in an accident near Iron Mountain, Michigan. The pilot and passenger sustained minor injuries. The airplane was operated under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight.

The pilot reported that he took off at a reduced winter takeoff power setting. Once airborne and established on a climb, he retracted the landing gear and flaps, added climb power in increments and input rate of climb (165 knots) on the autopilot and then noticed a generator control unit (GCU) annunciator display a failure. About the same time the pilot noticed the engine seemed quieter and the airspeed was decreasing. The pilot further increased the throttle lever, confirmed that the No. 1 fuel pump was switched on and the left fuel tank was selected, and then determined that the engine had shut down.

The pilot lined up with a clearing in the trees to his left; however, the airplane struck a small tree on approach to the clearing. The contact with the tree separated about half the outboard section of the right wing. The airplane touched down in rough, snow-covered terrain and came to rest with the engine and engine mount separated from the firewall. The pilot and passenger exited the wreckage from the entry door. The pilot stated that due to challenging terrain and poor options for a forced landing site he did not perform any other emergency procedures such as turning the fuel pump off, pulling the condition lever to idle cut-off, or feathering the propeller. Photographs taken by law enforcement following the accident show the condition lever in an unlatched position towards the idle cut off detent.

An onboard GPS and avionics unit captured data from the accident flight. Data showed that, at 0824:02 about 12 seconds after liftoff, torque and N1 (gas generator speed) reduced from 86.9% and 93.6% to 72.5% and 89%, respectively, with a simultaneous decrease in fuel flow (FF) from 62.2 gallons per hour (gph) to 53.7 gph and inter-turbine temperature (ITT) from 1114°F to 1011°F. About one second later indicated air speed (IAS) accelerated past 127 knots and the flap system indicated movement to a retracted position. At 0824:07 the autopilot was engaged and over the next 9 seconds heading (HDG) and IAS modes were selected, and IAS set to 165 knots.

During this time the torque decreased and stabilized at 41.5% for several seconds with a concurrent decrease in N1 to 84.8%, FF to 40.3 gph and ITT to 900°F. At 0824:21 all parameters are consistent with an engine shutdown. Six seconds later, the GCU FAIL light (governor control unit) illuminated. During the last 22 seconds of the flight, the airplane turned 54° to the left and lost about 490 ft of altitude while slowing from 117 knots (kts) to 96 kts. During this time, the engine torque and N1 were 0% with propeller speed slowing to 1270 rpm. 0824:49 marked the last datapoint with the autopilot engaged, with the fuel pressure at 35.6 PSI and voltage at 24.9 volts. The Garmin G3X data was recovered from records with a resolution of 1 time per second (1 Hz).

Based on Garmin data, the airplane had a recorded total fuel quantity of 118 gallons at the time of startup, consisting of 60 gallons in the left wing tank and 58 gals in the right wing tank. The last recorded data point indicated 57 gallons in the left tank and 60 gals in the right tank, totaling 117 gals. Fuel pressure was consistent from startup to the last record data point, varying from 30 to 35 psi. No data was able to be recovered from the turbine start limiting management system.

Figure 1 Accident Sequence

1. 8:24:02 - Engine starts to spool back.

2. 8:24:03 - Flaps retracted.

3. 8:24:07 - Autopilot engaged. Pilot starts data input in to autopilot (IAS).

4. 8:24:16 - Data entry complete, desired IAS set to 165kts.

5. 8:24:20 - Engine is flamed out.

6. 8:24:27 – GCU FAIL illuminates

7. 8:24:49 – End of recording

8. Accident location

Postaccident examination of the airframe fuel system did not reveal any anomalies that would have restricted fuel flow to the engine. The fuel filter located at the bottom of the header tank was impact damaged and the filter media was not recovered. Fuel lines were examined and found to be continuous with no anomalies or blockages noted. The fuel strainer was removed from the engine-driven fuel pump and examined; and some small particles of unknown origin were noted in the housing.

The engine-driven fuel pump and fuel control unit (FCU) were removed for functional testing at an overhaul facility. External damage was noted to both units consistent with the impact sequence. A solenoid, throttle linkage arm, and condition lever rod were replaced with serviceable parts on the FCU, and hardware was replaced on the fuel pump. Both units were installed onto a test engine, and leak tests were normal. The FCU was bled, and the engine started and ran at a lower power setting. It was then shutdown and bled again. The engine was started a second time and operated at rated power with the fuel pump both on and off with no anomalies noted. The engine power was manipulated from low to high several times with no anomalies noted. The engine was shut down and the units were sent to the manufacturer for disassembly. Although internal wear to the engine-driven fuel pump was noted, the FCU was unremarkable, and no anomalies were detected that could have resulted in a loss of engine power.