Ercoupe 415-C N94694 accident near Butterfield, Texas

Probable cause

A malfunction of the fuel transfer system for reasons that could not be determined based on the available information, a stuck float in the header tank sight gauge that resulted in an inaccurate fuel quantity indication, and the pilot’s inadequate monitoring of the wing tank fuel quantity during the flight, which resulted in a loss of engine power due to fuel starvation when the header tank became depleted of fuel.

NTSB analysis

The pilot was on a cross-country flight when the airplane's engine lost power during cruise flight about 1 hour 13 minutes after takeoff. The pilot stated that the wing fuel tank gauge indicated above 3/4 full and that the header tank sight gauge appeared "unchanged" from where it had been at departure. The pilot's corrective actions were unsuccessful in restoring engine power, and he conducted a forced landing to a dirt road. The airplane's left wing struck a small tree during the landing roll, which resulted in substantial damage to the left wing and twin vertical stabilizers. The pilot reported that the header fuel tank was empty after the accident, and each wing fuel tank contained about 7-8 gallons of fuel.

During normal operation, the engine-driven fuel pump transfers fuel from the wing tanks to the header tank, where it is gravity fed to the engine. A postaccident functional test of the header tank float-equipped sight gauge, which indicates the amount of fuel in the header tank, revealed the float would stick in the full up position and would remain stuck in that position despite vigorous shaking of the assembly by hand. There were no anomalies observed during multiple engine test runs, during which the engine-driven fuel pump functioned normally. Examination of the wing fuel tanks revealed significant pitting of the aluminum skins and peeling tank sealant. However, there was no evidence of an obstruction of the fuel lines when compressed air was blown through the fuel lines. The wing tank fuel shutoff valve was found in the on position and was secured by a rubber hose. The airplane was not equipped with an electric fuel pump. In the event of an engine-driven fuel pump failure or an obstructed fuel transfer line, the only fuel accessible to the engine was from the header tank. The reason why the engine-driven fuel pump did not continue to transfer fuel from the wing tanks to the header tank during the flight could not be determined with the available information.

Because the header tank sight gauge float was stuck in the full up position, the pilot did not have the normal visual indication that the header tank was being depleted of fuel during the flight. However, the pilot could have identified that fuel was not being transferred from the wing tanks to the header tank had he adequately monitored the wing fuel tank quantity gauge for a continual decrease throughout the flight. Had the pilot identified the fuel transfer issue before the header tank was depleted of fuel, he could have potentially landed before the engine was starved of fuel.

Text from the NTSB. Open the NTSB docket for CEN17LA089 for the full record.