Incident Overview
An aircraft experienced fuel exhaustion after 3 hours and 41 minutes of flight, significantly short of the planned endurance. The pilot reported being confident that the fuel tanks were full at takeoff.
Flight Planning Data
Preflight planning and a documented conservative fuel burn rate indicated the aircraft should have been able to remain airborne for at least 4 hours and 37 minutes. This calculation was based on a fuel burn rate of 13 gallons per hour and a total fuel capacity of 60 gallons.
Post-Accident Examination
An examination of the fuel bladder cells revealed several loose retaining clips and general collapsing and distortion of both cells. These conditions could reduce usable fuel capacity, potentially explaining the discrepancy between planned and actual endurance.
Maintenance History
According to the aircraft logbook, the airworthiness directive (AD) intended to remedy the bladder cell issue was complied with 41 flight hours prior to the accident. Despite this compliance, the cells were found to be collapsing and distorted.
Conclusion
The aircraft ran out of fuel after 3 hours 41 minutes of flight. The exact cause of the reduced endurance was not determined, but the distorted fuel bladder cells with loose retaining clips were noted as potential contributing factors to fuel unavailability. The source does not state a probable cause.