N68XA

On July 31, 2023, about 0920 Pacific daylight time, an experimental amateur-built Lancair 360 airplane, N68XA, was substantially damaged when it was involved in an accident near Renton, Washington. The private pilot and passenger were seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

According to the pilot, the cross-country flight began in central California two days before the accident. His last fuel stop on the first day of flying was in Scappoose, Oregon, where he topped off the fuel tanks. He then departed with 43 gallons of fuel onboard and flew 1 hour to William R Fairchild International Airport (CLM), Port Angeles, Washington, where he stayed overnight. The following day he flew to Renton Municipal Airport (RNT), Renton, Washington, and then returned to CLM, for a total of about 50 minutes of flight time between the two flights that day.

On the day of the accident (the next day), he flew back to RNT, which took about 25 minutes. After an uneventful flight, he entered a 45° approach to the downwind leg of runway 34 to enter the traffic pattern. Once the airplane was established on the downwind leg the pilot began the pre-landing checklist; however, after he deployed the flaps and landing gear, “the engine turned slower” and the instruments flickered. The pilot then informed air traffic control (ATC) that he needed to land.

Almost immediately, the engine returned to full power, which the pilot reported to ATC as he figured the brief power loss was an isolated event. The pilot stated the engine then lost power, and the engine monitor turned off when the airplane was midfield during the downwind leg. Data retrieved from the engine monitor showed a portion of the accident flight; however, the unit did not capture the loss of power. The pilot selected a gap between two transport-category airplanes. He flew between and just above them. He then made a right turn to align the airplane with runway 34. Subsequently, the right wing dipped and the airplane stalled. According to the pilot he could not recount any further events.

The airplane sustained substantial damage to the empennage.

Postaccident examination of the airplane revealed no preimpact mechanical anomalies that could have precluded normal operation.

The engine was equipped with a plasma capacitor discharge ignition (CDI) system, manufactured by Light Speed Engineering, LLC. According to the operation manual, all plasma CDI systems can be used with 12-volt electrical systems. The minimum supply voltage for starting is 6.5 volts and the minimum operating voltage is 5.5 volts.

The CDI manual contains operating instructions for systems with main and auxiliary batteries. According to the manual,

“Dual Systems only: If you have installed an aux battery per the LSE supplied drawing, monitor your voltmeter and do not switch to the aux battery until the supply voltage of the main battery is below 6.5 Volts or the engine is not running smoothly. After switching to the aux battery, your voltmeter will read the voltage remaining in your aux battery.”

The manual did not include any emergency procedures that required the pilot to switch batteries inflight.

The electrical system was powered by a 12-volt main battery with an additional 12-volt auxiliary battery. Two solenoids drew power from the main and auxiliary batteries to deliver power to the starter motor. The pilot can toggle between both batteries using switches located on the instrument panel labeled “IGN A” and “IGN B.” The switches are used to select either the main or auxiliary batteries to run the electronic ignition system (“IGN A” runs 4 spark plugs and “IGN B” runs another 4 spark plugs).

The airplane was equipped with a voltage meter located within the display of the onboard engine monitor and a low voltage light. The pilot reported that he did not observe the light illuminate throughout most of the flight; however, he reported that he was not focused on it after the instrument panel went “dark.”

According to the onboard engine monitor, the voltage indicated 14vdc about one hour and 20 minutes prior to the accident.

Figure 1: Battery switches on instrument panel

Both batteries remained within their respective bays between the instrument panel and engine firewall. The negative terminal of the main battery was fractured and exhibited evidence of arcing. The positive leads were secured to the positive terminal of the battery and were unremarkable, as were both terminals on the auxiliary battery. The main battery voltage measured 3.67 volts and the auxiliary battery voltage was 12 volts when tested with a multimeter.

The examination also revealed two indentations on the lining of the composite battery compartment cover. The location of the indentations corresponded with the position of the negative and positive terminal connections (see Figure 2).

Figure 2: Composite battery compartment cover with aux and main battery positions

A metallurgical examination of the negative main battery terminal revealed that it fractured in overstress. There was also evidence of arcing on the nut of the negative terminal. The remelt spot in the arcing exhibited elevated copper relative to the surrounding areas.

Figure 3: Main battery, negative terminal

Postaccident examination of the engine revealed no additional preimpact mechanical anomalies or malfunctions that would have precluded normal operation. All four electronic ignition boxes remained securely attached to their mounts and each ignition harness was securely connected to both its respective ignition box and spark plug. The top spark plugs were all tightly secured and each plug exhibited coloration consistent with normal wear when compared to the Champion Check-A-Plug chart (AV-27).

Metallurgical examination of the positive terminal fracture signatures revealed they were consistent with ductile overstress from torsional loads. The fracture surfaces of the negative terminal were mostly smeared consistent with sliding contact between the mating fracture faces under mostly shear loading with limited tensile stresses in the fracture plane.

Arc damage was found on the negative terminal that had peaks associated with copper.