What happened
On 21 January 2017, a Cessna 177A, registration N707XJ, was performing a general aviation flight from Shannon Airport to Navan Airfield via Weston Airport. While cruising at approximately 1,500 feet near Clarkestown Mast in Co. Meath, the aircraft experienced a sudden loss of engine power, causing the propeller to begin windmilling.
The pilot issued a MAYDAY call and identified a suitable grass field for an emergency landing. To ensure the aircraft reached the field despite the loss of altitude, the pilot opted to land with a tailwind component on a downhill slope. The landing involved several bounces due to the terrain, but the aircraft came to a stop without any damage or injuries to the three occupants.
The investigation
Investigators examined the fuel management procedures used prior to departure. Before leaving Shannon, the pilot had used a dipstick to check the fuel levels. Because the aircraft's left fuel gauge was inoperable and the right gauge was considered unreliable, the pilot relied on this manual measurement. The pilot believed the aircraft contained 26 USG of fuel, which was deemed sufficient for the planned route.
Upon inspection, the AAIU determined that the dipstick used was actually intended for a Cessna 172, not the Cessna 177A. Because the fuel tank geometry in the 177A is non-linear, the 172 dipstick provided a significantly inflated reading. While the pilot believed there were 26 USG on board, the actual total fuel load was only approximately 12.2 USG.
Findings
- The engine power loss was caused by fuel starvation.
- The pilot used an incorrect dipstick, which was designed for a different aircraft type (Cessna 172).
- The use of the incorrect tool resulted in an erroneous estimate of the fuel load, which was less than half of the expected amount.
- The pilot's reliance on manual measurements was necessitated by inoperable or unreliable cockpit fuel gauges.