On September 17, 2020, about 1810 central daylight time, a Cessna 177RG airplane, N2699V, was substantially damaged when it was involved in an accident near Wheeling, Illinois. The pilot was not injured. The airplane was operated under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. According to the pilot’s statement, the accident occurred on the third flight of the day. At the start of the flight, the fuel flow/pressure gauge displayed 9.5 gallons (he initially reported 6.5 gallons to a National Transportation Safety Board investigator). About 3 minutes after takeoff, the engine lost partial power. The pilot was unsuccessful in restoring engine power, so he elected to perform a forced landing to a road. During the landing roll, the right wing collided with a utility pole. Substantial damage was sustained to the airplane’s right wing and empennage. The fuel flow/pressure gauge displayed a fuel quantity of 5.5 gallons at the accident site. A postaccident engine run was conducted using the fuel that remained on the airplane. The engine ran without any anomalies. There was no contamination observed in the fuel lines from the fuel filter assembly to the fuel pump, fuel pump to the fuel controller, and from the fuel controller to the flow divider. The fuel flow transducer was examined, and no anomalies were observed. After the run was completed, 1 gallon of fuel was drained from the airplane, which appeared uncontaminated. A review of the airplane’s type certificate data sheet revealed the unusable fuel quantity for a Cessna 177RG was 1 gallon. Documentation for the Electronics International Inc. FP-5 fuel flow/pressure gauge states: The fuel remaining displayed by the FP-5 is not a measurement of the fuel in the tanks. It is an amount calculated from the starting fuel level you programmed into the FP-5, minus the fuel used while the engine was running. Even after verifying the calibration of the FP-5 it should never be used as the primary indicator of fuel quantity in the tanks. It is important the pilot visually check/measure the fuel quantity for each tank before takeoff and cross-check these readings against the Fuel Level Gauges and the FP-5. It is possible for any instrument to fail thereby displaying inaccurate high, low, or jumpy readings. Therefore, you must be able to recognize an instrument failure and you must be proficient in operating your aircraft safely in spite of an instrument failure.