Amateur-built II N169BF accident near Fishers, Indiana

Probable cause

The airplane’s total loss of engine power due to fuel exhaustion as a result of leaking fuel from a loose fuel inlet fitting to the fuel control unit.

NTSB analysis

The pilot was conducting a post-maintenance flight in the experimental airplane to “break-in” two engine cylinders that were replaced on the day before the accident. The engine was operated at maximum speed with a full rich mixture setting throughout the flight. The pilot stated that the airplane lost total engine power about 1 hour after takeoff. During the forced landing, the airplane impacted a street signpost, resulting in substantial damage to a structural fuselage tube.

The pilot reported that the fuel tank contained 23 gallons of fuel at the start of the flight. Postaccident examination found that the airplane’s fuel tank was empty and that only 2 to 3 fluid ounces of fuel were recovered from the fuel system. Evidence of a fuel leak was found within the engine compartment and on the exterior lower fuselage skins aft of the firewall. Examination of the fuel system revealed that the fuel inlet fitting to the fuel control unit was finger tight.

In preparation for a postaccident engine test, the loose fuel inlet fitting was tightened, and the fuel system was pressurized to confirm that no other leak sources existed. The engine started and ran normally without any hesitation, stumbling, or interruption in power. There was no evidence of a fuel system leak following the engine run.

Based on data collected during the engine test, the fuel consumption rate at maximum engine power on the ground (static power) was about 13.69 gallons per hour (gph) at an engine speed of 2,260 rpm. The estimated fuel consumption rate while in flight at maximum engine power (2,800 rpm) was about 16.96 gph. With a full fuel tank (23 gallons) at departure, the airplane’s fuel endurance was about 1 hour 21 minutes if the engine was operated at maximum power with a full rich mixture setting.

Other than the loose fuel inlet fitting, the engine examination and test run revealed no mechanical malfunctions that would have prevented normal engine operation during the flight. Air traffic control radar data showed that the airplane was airborne for about 1 hour 15 minutes during the accident flight. Thus, it is likely that the loose fuel inlet fitting leaked fuel during the flight, which resulted in fuel exhaustion and the subsequent total loss of engine power.

Text from the NTSB. Open the NTSB docket for CEN21LA386 for the full record.