CEN23LA273 · Berkut 540

According to the pilot, the accident occurred during his first flight of the experimental airplane. About 8 minutes after takeoff, upon reaching an altitude of about 3,250 ft mean sea level (msl), the airplane entered a gradual descent, and the pilot realized that the engine had lost partial power. He decided to return to the airport. He recalled the fuel pressure, fuel flow, and manifold pressure were within normal limits at that time. However, when the pilot activated the fuel boost pump, the engine lost all power. The airplane did not have sufficient altitude to reach the airport, and the pilot executed a forced landing to a road.

The airplane impacted a sign and trees adjacent to the road before coming to rest in a residential driveway. The pilot noted that when the airplane came to rest, he heard a “fast humming” sound and immediately switched off the ignition. Both wings separated from the fuselage, and both canards were damaged. Each of the four propeller blades were separated at the blade roots and fragmented.

A postaccident engine examination revealed several anomalies. The ignition harness leads corresponding to the Nos. 3 and 4 cylinder upper spark plugs were disconnected from the ignition module. In addition, the Nos. 1, 2, and 6 upper, and the No. 2 lower spark plug leads were loose and not fully connected at the ignition module. The ignition modules were tested and operated normally. The Nos. 1 and 2 cylinder spark plugs exhibited normal operating signatures; however, the remaining spark plugs exhibited sooty deposits.

Engine data retained by the onboard avionics revealed the engine speed remained stable until about 6 minutes after takeoff when it decreased about 200 rpm consistent with a partial loss of engine power. At that time, the No. 1 cylinder head temperature (CHT) and exhaust gas temperature (EGT) decreased dramatically. The No. 2 CHT and EGT remained low for most of the flight.

About 14 minutes after takeoff, the engine speed decreased further from approximately 2,500 rpm to about 1,200 rpm with corresponding decreases in the other engine parameters. Approximately 15 seconds after the reduction in engine power, the fuel pressure increased consistent with the pilot activating the electric fuel boost pump. About one minute after the reduction in engine power, the pilot touched down on the road during the forced landing, and six seconds later the engine speed and fuel flow increased abruptly and momentarily and then abruptly dropped to zero.

The sudden increase in engine speed after impact suggested the engine had not lost power completely, and the engine speed increased when the propeller blades fractured during the accident sequence, which removed the resistive torque from the engine.

The partial loss of engine power was likely due to the ignition system anomalies observed during the postrecovery examination.

Verbatim NTSB analysis and probable cause from the NTSB dataset