Cessna P210N N36RW

The pilot departed the airport, after estimating with a calibrated stick that the airplane had 20 gallons of fuel in the left tank and 1/2 gallon of usable fuel in the right tank, for a 13-minute flight to the airplane’s home airport. The pilot selected the left fuel tank for the flight. About 3 minutes into the flight, or about 6.5 miles from the airport, he received indications of an insufficient rate of electrical charge; he did not attempt to reactivate the alternator as outlined in the Pilot’s Operating Handbook but elected to return to the airport. ADS-B showed that the airplane, which was about 6.5 miles southwest of the airport, then turned left 180° followed by a shallow continuous left turn for the next 5 miles while maintaining an altitude of about 6,400 ft msl. The airplane then turned right and began to descend toward the airport, entering the base leg for runway 26. The pilot then prepared to lower the gear manually due to the low voltage indication when, “seconds later,” the engine lost power. Once the landing was assured, the pilot lowered the landing gear handle, which activated the battery-driven hydraulic pump that controlled the landing gear system. The pilot reported that, after touchdown and despite his control inputs, the airplane veered sharply left, then sharply right, before exiting the runway into gravel. The impact with terrain substantially damaged the left horizontal stabilizer and elevator. Postaccident examination of the airplane’s fuel system revealed that about 6 gallons of fuel remained in the left wing tank and no usable fuel remained in the right wing fuel tank following the six-minute flight. The pilot reported that fuel was leaking from the left wing and front cowl after the accident, until the airplane was moved. According to the manufacturer, the last 0.5 gallon of fuel in the tanks are unusable. A test run of the engine revealed that it operated normally. The examinations revealed no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation. The pilot reported that the airplane had an electrical issue before the annual inspection and suspected the alternator, which was replaced in 2020. Engine data monitor (EDM) data confirmed that after takeoff there was a continuous loss of battery voltage while the flight progressed. During the postaccident examination, one wire and a grounding strap were movable with hand force; however, the alternator and voltage regulator tested normally, and the alternator field circuit breaker was secured in place. No reason for the loss of voltage could be determined. The low battery voltage was insufficient to power the hydraulic pump to fully extend and lock the landing gear, which resulted in its collapse upon touchdown. The EDM data also revealed that, while the airplane was on the base leg to land and immediately before the loss of engine power, a reduction in fuel flow was followed immediately by an increase in engine exhaust gas temperatures. Such an increase is consistent with a lean fuel-to-air mixture, as often occurs during the initial phases of a fuel exhaustion or starvation event. ADS-B data showed the airplane maneuvered continuously during the return portion of the flight; the airplane likely entered sufficient uncoordinated flight while maneuvering to uncover the left wing fuel tank’s supply outlet, starving the engine of fuel and resulting in the total loss of engine power.

Quoted verbatim from the NTSB record.