ERA24LA331 · Aero Commander 200 D

After filling the fuel tanks, the flight instructor flew the airplane on multiple flights with different fuel tanks selected, including the right main fuel tank, with no discrepancies. The instructor and a pilot who was receiving familiarization training in the airplane then departed with the fuel selector on the right main fuel tank. They performed airwork with the fuel selector on a different tank before switching back to the right main fuel tank for an approach and landing. Before departing again, the pilot and instructor reviewed the fuel quantity indications and decided to keep the fuel selector on the right main tank position because the indicated quantity appeared sufficient to sustain engine operation. After departure, the flight remained in the airport traffic pattern. After turning onto the downwind leg, the engine lost power, regained it momentarily, then lost power completely. Turning on the auxiliary fuel pump did not restore engine power. The flight instructor took control of the airplane and elected to land in a field after determining the airplane could not reach a closed runway at the airport. After touchdown, the airplane bounced then came to an abrupt stop with substantial damage to both wings and the fuselage.

Postaccident examination of the airplane determined that the right main fuel tank had collapsed inward despite no corresponding damage to the surrounding wing structure and wing skin. Further examination of the right main fuel tank’s fuel vent line utilizing compressed air found that an insect nest had extensively blocked it. This blockage would have prevented air from entering the tank as fuel was consumed and allowed a partial vacuum to develop inside the tank. The inward collapse also trapped the fuel quantity transmitter arm, and resulted in the fuel quantity gauge indicating more fuel than was actually present. As fuel continued to be consumed from the unvented tank, the erroneous fuel quantity indication prevented the flight crew from accurately assessing the remaining usable fuel. Before the takeoff that preceded the loss of engine power, the pilots selected the right main fuel tank based on the indicated fuel quantity, although the tank actually contained insufficient usable fuel. After departure, the engine lost total power due to fuel starvation when the fuel remaining in the selected tank was exhausted. Although the pilots activated the auxiliary fuel pump and the instructor directed the left-seat pilot to select another fuel tank, selection of the right fuel tank did not occur before the pilots’ attention became solely focused on executing the forced landing.

Verbatim NTSB analysis and probable cause from the NTSB dataset