What happened
On July 13, 2008, a Cessna 172, registration CS-AHX, was conducting an aerial advertising banner tow along the Algarve coast near Vilamoura, Portugal. During the cruise phase of the flight, the pilot noticed a significant loss of engine power. Although cockpit instruments indicated that engine parameters were within normal ranges, the engine could not maintain the required flight path, forcing the pilot to descend to maintain airspeed.
In response to the power loss, the pilot released the advertising banner and searched for a suitable location for an emergency landing. The pilot successfully landed the aircraft in an uncultivated agricultural field near the Vilam/Loulé wastewater treatment plant. The landing was performed without damage to the aircraft, and the pilot remained uninjured.
The investigation
Following the incident, investigators examined the engine and identified a fracture in the metal fuel supply line serving cylinder number three. The failure occurred at the weld point where the line connects to the retainer head near the injector. The investigation established that while the line remained attached to the fuel control unit, fuel was leaking externally, which caused a drop in fuel pressure throughout the line. This leak resulted in a dead cylinder and insufficient pressure to the remaining cylinders to produce necessary power.
Findings
- The primary cause of the power loss was a fracture in the fuel supply line for cylinder number three.
- Although the fuel lines were equipped with soft clamps for potential attachment points, the lines were not actually secured or tied down along their length.
- Because the lines were only fixed at their ends, engine vibrations propagated through the tubes, leading to material fatigue and eventual failure at the weld point.
- The failure occurred in a high-temperature zone of the engine, creating a potential fire hazard due to fuel spraying onto hot cylinders.