ERA12FA023 · SOCATA TBM 700

In anticipation of the maintenance test flight, a about 72 gallons of fuel was added to the left fuel tank to balance the fuel load. During the preflight, the pilot noted that the left tank had 105 gallons and that the right tank had 108 gallons. Because of the fuel level indications, the pilot did not visually inspect the tanks; even if he had done so the wing dihedral would have prevented him from seeing the fuel level.

About 20 minutes after takeoff, the pilot received the first annunciation of "Fuel Low R," which lasted for about 10 seconds then went out. This indicates the fuel quantity is less than or equal to 9 gallons of usable fuel in the right tank. The pilot attributed this to a malfunction of the low fuel level sensor, since the fuel gauge showed about 98 gallons of fuel. He instructed the right front seat occupant (the mechanic) to make a note so the sensor would be replaced after the flight. Shortly thereafter, the amber "Fuel Unbalance" illuminated, and indicated that the right fuel quantity was greater than the left; as a result the pilot switched the fuel selector to the right tank.

He then initiated a descent to 10,000 feet to perform system checks, and after levelling off at that altitude for about 15 minutes, received a second "Fuel Low R" annunciation; he verified that the fuel selector automatically switched to the left tank and noted that the message went out after about 10 seconds. Either before or during a descent to 4,000 feet, the second "Fuel Unbalance" annunciation occurred. The right tank again depicted a greater quantity of fuel, so the pilot again switched the fuel selector to the right tank. The flight continued to a nearby airport, where the pilot terminated an instrument approach with a low approach. The flight then proceeded to the destination airport and entered the traffic pattern on a left downwind leg..

While on the downwind leg, the pilot received the third "Fuel Unbalance" annunciation and at this time the left fuel gauge indicated 55 gallons while the right fuel gauge indicated 74 gallons. Because he intended to land within a few minutes, the pilot manually selected the fullest (right) tank, then turned to base then final. While at 800 feet on final approach, the red warning message "Fuel Press" illuminated and the engine lost all power. Attempts to restore engine power were unsuccessful. Unable to reach the airport, the pilot landed on a nearby turnpike. Both fuel tanks were breached, and fuel leakage, likely from the left fuel tank, was noted at the site. Inspection of the fuel outlet filter on the engine and the fuel sequencer reservoir considered an airframe item revealed both contained minimal fuel consistent with fuel starvation from the right fuel tank that actually did not contain an adequate supply of fuel.

Postaccident operational testing of the engine revealed no evidence of preimpact failure or malfunction that would have resulted in the loss of power. Examination and testing of the right fuel gauge harness revealed that a high impedance shielded cable was not correctly soldered to the shielding braid when the airplane was manufactured, which resulted in erroneous high readings of the fuel quantity in the right tank.

Several opportunities existed to detect the fuel quantity errors in the right tank during the airplane's 600-hour and annual inspection, which was signed off the day before. Several times during the inspection, electrical power was applied and different fuel quantities for the right tank were displayed, yet nothing was done to determine the reason for the different fuel indications. For example, 41 gallons was displayed, yet 70 gallons was drained; the fuel was returned to the tank after maintenance, yet the gauge showed 51 gallons, and after a post-maintenance run was performed, the gauge showed over 140 gallons even though it hadn't been fueled. Maintenance personnel incorrectly attributed the difference to fuel migration. Further, the pilot had the opportunity to terminate the test flight after multiple conflicting indications from the right tank, yet he continued the test flight, which resulted in fuel starvation.

Verbatim NTSB analysis and probable cause from the NTSB dataset