Overview
On February 9, 2021, at 1453 eastern standard time, an experimental, amateur-built Vans RV7, registration N611E, was substantially damaged when it impacted terrain during a forced landing near Thonotosassa, Florida. The private pilot, who was also the builder of the aircraft, sustained minor injuries. The airplane was operating under Title 14 Code of Federal Regulations Part 91 as a test flight during Phase 1 flight testing.
Accident Details
The pilot reported that two days before the accident flight, the airplane experienced a loss of fuel pressure and a total loss of engine power. He executed a successful forced landing without injury, and subsequent inspection revealed no damage to the aircraft. Examination of the engine found that the fuel pressure adapter “T”-fitting, used to attach the fuel pressure line, had disconnected from the fuel pump elbow fitting.
The adapter fitting had been adopted during the aircraft’s construction for fitment in a confined space. Reattachment of the fitting was accomplished using a modified and shortened 5/8-inch spanner wrench for the 11/16-inch B-nut. After reattachment, the pilot departed the forced landing site and landed successfully at his destination.
On the accident flight, minutes after departure, the airplane again experienced a loss of fuel pressure and a total loss of engine power. During the ensuing forced landing, the pilot sustained minor injuries and the airplane was substantially damaged. Post-accident examination revealed that the same fuel pump elbow fitting was disconnected from the adapter fitting.
Aircraft and Flight History
The airplane’s airworthiness certificate was issued on January 21, 2021. According to the pilot, the first loss of engine power occurred at about 3.5 total aircraft hours, and the second total power loss occurred at about 4.1 total aircraft hours.
Post-Accident Examination
A Federal Aviation Administration aviation safety inspector recovered the adapter fitting and performed rudimentary, comparative hand-tightened torque applications using both the shortened, modified wrench and a standard 11/16-inch spanner. The results of these tests were recorded.
The pilot stated that the aluminum adapter fitting, which attached to the steel fuel pump elbow fitting, was purchased at an automotive speed shop.
Laboratory Analysis
The fitting and associated parts were examined at the NTSB Materials Laboratory. Examination and research revealed that the material hardness of the aluminum adapter fitting was below an Air Force Navy (AN) military specification. The manufacturer of this automotive fitting stated that there was no specified torque value but that the fitting should be tightened to a “snug” condition. Multiple sources cited a torque value of 150 to 195 inch-pounds or the “flats” method (1 to 1.5 flats past finger tight).
When the flats method was attempted in the laboratory, two to three times the specified torque value was required to rotate one flat. Once the nut was removed, the shoulder of the adapter body displayed damage. Additionally, the body of the adapter fitting rotated when torque was applied to the nut. The movement of the adapter fitting created the potential for stresses in the fuel lines to apply force in the loosening direction.
Pilot Statement
In the pilot’s NTSB Form 6120.1 Pilot/Operator Accident Report Form, he stated, “Fuel line 'T' fitting disconnected from engine fuel pump fitting elbow most likely due to improper torquing.”