CEN24FA218 · Cessna 172 R

The flight instructor and student pilot departed the airport, performed several flight maneuvers, and then flew to another airport to practice takeoffs and landings. On the third takeoff, the flight instructor informed the student pilot that they were low and no longer climbing. The flight instructor attempted to add more power, but the engine quit, and the propeller windmilled. The flight instructor glided the airplane to a field, hit the ground hard, bounced, and came down harder. ADS-B data revealed they had been flying for about 1 hour before the engine lost power. The airplane was serviced with 32.4 gallons of fuel before the flight. Aviation fuel could be smelled at the accident site and fuel blight was present on the ground underneath the airplane. Additionally, the fuel strainer bowl contained fuel. Postaccident examination of the engine revealed that the engine-driven fuel pump was tightly installed to the accessory section of the engine. The hose from the fuel pump to the fuel servo had about 1 ounce of fuel in it, the line from the outlet of the fuel servo to the fuel manifold had trace amounts of fuel, and a trace amount of fuel was found within the fuel manifold. There was no fuel in any of the 4 injector fuel lines. The top 5 screws on the engine-driven fuel pump were loose. The manufacturer stated that before the fuel pumps are stocked or shipped from their facility, they are visually inspected, at which time torque striping is applied to at least 2 of the screws. The fuel pump on the accident airplane had a torque stripe on one of the top screws and 2 of the bottom screws. All 3 torque stripes were aligned and unbroken. The airplane’s engine was overhauled and a new engine-driven fuel pump was installed about 5 years before the accident. The fuel pump was not a field-serviceable unit, and a review of maintenance logbooks revealed no evidence that the fuel pump was removed or serviced once it was installed. Because the 3 torque stripes on the screws on the fuel pump were aligned and unbroken at the time of the accident, and the fuel pump was not serviced or removed after it was installed on the overhauled engine, the top 5 screws on fuel pump likely were loose because they were improperly torqued before leaving the fuel pump manufacturing facility. According to the fuel pump manufacturer, if the screws are not properly torqued, the clamping force on the top 2 diaphragms could be compromised, which could lead to the fuel pump ingesting air and not operating properly. During postaccident testing of the fuel pump, air bubbles and oil were observed along the split line of the top cap. All diaphragms were intact with no damage or debris. The lack of a tight seal on the engine-driven fuel pump likely introduced air into the line that led to the fuel servo, which interfered with proper fuel metering within the fuel servo. The air intrusion would have disrupted the servo’s ability to meter fuel accurately because the servo relies on consistent fuel pressure and density to regulate flow. When air was present in the line, the associated pressure drop likely resulted in insufficient fuel delivery to the fuel manifold. The toxicological results for the flight instructor indicated use of the medication diphenhydramine which has a potential to cause sedation and cognitive psychomotor slowing. Although the pilot may have experienced impairing effects of this medication at the time of the accident, no more specific conclusion of this impairment was drawn.

Verbatim NTSB analysis and probable cause from the NTSB dataset