Accident Overview
On October 21, 2023, at approximately 1340 Eastern Daylight Time, a Cessna 172L, registration N7716G, was substantially damaged during an accident near Richmond, Virginia. The flight instructor, student pilot, and one passenger were not injured. The aircraft was operating under Title 14 Code of Federal Regulations Part 91 as an instructional flight.
Flight and Engine Failure
The flight instructor reported that the purpose of the flight was to conduct a review of flight maneuvers in a designated practice area. While returning to the airport (OFP), the engine began to lose power. The power loss progressed until the airplane could no longer maintain level flight. The flight instructor initiated an emergency landing in an open field short of the runway. During the landing rollout, the right wing struck a tree, resulting in substantial damage.
Post-Accident Examination
A Federal Aviation Administration inspector examined the aircraft on site. The right wing exhibited damage consistent with impact with a small tree at the accident site. The cabin section showed damage at the right-wing root attachment area, and the left wing displayed upward bending from the wingtip about 2 feet inboard.
An engine examination established valvetrain continuity with crankshaft rotation through 720 degrees. Ignition continuity was confirmed during inspection of the magnetos, ignition wires, and spark plugs. An undetermined amount of fuel sufficient for flight was found in both fuel tanks.
Carburetor Analysis
The carburetor was partially disassembled. The float bracket had fractured into two pieces. The float remained attached to the bracket by the float lever shaft, and the float valve was coupled to the float by a clip mounted on the float lever shaft. The float’s movement along the shaft allowed axial motion of the float valve within the float valve seat, restricting fuel flow into the bowl when the valve sealed against the seat.
Carburetor components were submitted to the National Transportation Safety Board (NTSB) Materials Laboratory for further examination. Analysis revealed that one arm of the float bracket had fractured due to cyclic fatigue. The fracture surface was flat with radiating lines and curved crack growth features consistent with fatigue failure. The origin of the fracture was along the interior edge where the bracket arm intersected the base of the bracket. No anomalies were observed at the fracture origin.
Maintenance History
A review of logbook excerpts noted that in 2005 an IRAN (Inspect & Repair As Necessary) was performed, which included replacement of various original accessories, including the carburetor. No other maintenance on the carburetor was recorded since 2005.