Amateur-built LANCAIR 360 N68XA accident near Renton, Washington

Probable cause

A loss of electrical power due to low battery voltage, which resulted in an inflight shut down of the capacitor discharge ignition system and a loss of engine power. Contributing to the accident was the pilot’s failure to switch batteries after the electrical power loss.

NTSB analysis

The pilot was preparing to land when the accident occurred. Once the airplane was established on the downwind leg of the traffic pattern, he extended the landing gear and the engine immediately began to lose power and the instruments started to flicker. Shortly thereafter, engine returned to full power and then lost all power. The pilot immediately turned toward the airport to make a midfield landing. He attempted to maneuver the airplane to align it with a runway, but a wingtip contacted the runway and the airplane impacted the ground, which resulted in substantial damage to the empennage.

The airplane was equipped with an onboard capacitor discharge ignition (CDI) system instead of magnetos. The system operates on a 12-volt (v) battery. Postaccident examination revealed the main battery voltage was 3.67 volts and the auxiliary battery voltage was 12 volts. The pilot was operating the system off the main battery at the time of the power loss. The minimum supply voltage for starting the engine is 6.5 volts and the minimum operating voltage is 5.5 volts. There were no emergency procedures that would have required the pilot to switch batteries. However, as the functionality of the CDI was contingent on battery power, a logical and conscientious troubleshooting step would have been to verify battery voltage and switch batteries. The engine would have continued to run as the auxiliary battery voltage exceeded the minimum supply voltage for the CDI.

The examination did not reveal any additional preimpact mechanical anomalies of the engine or airplane that would have precluded normal operation. The airplane’s onboard engine monitor did not capture the loss of power, likely because the unit had shut down when the loss of electrical power occurred.

The CDI and airplane’s electronic systems were drawing power from the main battery, which was providing insufficient voltage at the time of the accident. The power loss likely occurred when the pilot extended the landing gear, which may have drawn enough power to place the battery beneath the minimum operating voltage of the CDI. This critically low voltage would have resulted in a loss of power to the electrical system and electronic magnetos, which would have resulted in a loss of power to the engine. The investigation also found that the battery terminal connections were likely in contact with their composite cover at the time of the accident, which resulted in their separation from the battery during the accident sequence due to overstress.

Text from the NTSB. Open the NTSB docket for WPR23LA295 for the full record.