What happened
On March 18, 2011, at approximately 17:30 UTC, a Piper PA-28-180, registration I-ONIL, was conducting a training flight departing from Grosseto airport. The aircraft was occupied by an instructor pilot, a student pilot, and one passenger. Approximately 20 minutes into the flight, the engine ceased operation. After several unsuccessful attempts to restart the engine, the pilot performed a forced landing in a flat, soft agricultural field near Albinia, Orbetello.
During the landing sequence, the soft nature of the terrain caused the nose and main landing gear struts to collapse. The aircraft slid approximately 15 meters on its fuselage belly. While there were no fatalities, the two occupants in the front seats sustained minor abrasions from impacting the dashboard. The aircraft sustained significant damage, including a deformed propeller blade, separation of the landing gear struts, and damage to the wing surfaces and fuselage.
The investigation
The ANSV investigation focused on the cause of the engine failure and the condition of the fuel system. Post-accident inspections revealed that a significant amount of water—exceeds one liter—was present in the right wing tank, the gas-cooler filter, and the carburetor bowl.
Investigators examined the fixed underground refueling station managed by the Aero Club used to refuel the aircraft prior to the flight. The inspection of the fueling system revealed that the entire delivery circuit, including the electric pump, the flexible hose, and the terminal filter, contained a mixture of water and fuel. The electric pump was found to be seized.
Further examination of the underground storage tank revealed a layer of water approximately one centimeter thick at the bottom of the tank. The inspection of the tank's access manhole showed advanced corrosion on the cover and connected metal piping. Crucially, the vent pipe was found to have completely corroded and detached from the manhole cover.
Findings
- The primary cause of the engine failure was water contamination in the fuel supply.
- The detachment of the vent pipe from the storage tank manhole likely allowed water to flow into the fuel cistern during the most recent refueling operation.
- The presence of water in the fuel system was confirmed by the discovery of liquid in the right wing tank, the gas-cooler, and the carburetor.
- The refueling infrastructure was compromised by significant corrosion and a failure in the ventilation system, which allowed water to enter the fuel stock.