Cessna 172 N80457 accident near Key Biscayne, Florida

Probable cause

The nearly complete blockage of the right fuel tank strainer with organic material, which resulted in fuel starvation and the subsequent total loss of engine power. Contributing to the fuel starvation was the pilot receiving instruction’s and the flight instructor’s failure to identify that the fuel was burning unevenly during the flight.

NTSB analysis

The flight instructor stated that, during the preflight inspection, he visually inspected both fuel tanks and checked the fuel level using a dipstick and that each tank contained about 15 gallons. Subsequently, the flight instructor and private pilot receiving instruction departed for an instrument training flight with the fuel selector positioned to the "both" position. The pilots flew to two different airports to practice instrument approaches and holding. About 2 hours 25 minutes after the airplane originally departed, the flight instructor chose to return to the departure airport. The instructor stated that, while east of the airport, the engine "sputtered" for about 2 to 3 seconds and then lost all power; the engine rpm then increased briefly to 1,500, followed by the loss of all engine power again. The pilot reported that, at that time, the left and right fuel gauges were in the lower red arc between 1/4 and 1/2 capacity, respectively. The pilots attempted to restore engine power by moving the fuel selector to each fuel tank position and checking the magnetos in each respective position to no avail. The instructor maneuvered the airplane for a forced landing on a road, during which it collided with trees and a light pole before landing hard.

During postaccident examination of the airplane, less than 1 gallon of fuel was drained from the left fuel tank, and about 10 gallons of fuel were drained from the right fuel tank; the tanks were not breached, and no evidence of leakage was found. Further examination of the right fuel tank supply system revealed that the strainer was nearly completely blocked by organic material, which prevented the remaining fuel in the right fuel tank from feeding to the engine and likely resulted in the loss of all engine power due to fuel starvation. If either the flight instructor or the pilot had scanned the fuel quantity gauges periodically throughout the flight, they could have noticed the uneven fuel burn and performed a precautionary landing before the engine lost power.

Text from the NTSB. Open the NTSB docket for ERA17LA242 for the full record.