What happened
On September 18, 2010, at 19:50 local time, a SLEPCEV STORCH SS-4, registration EC-JUH, was performing a local flight near the Casarrubios del Monte aerodrome in Toledo, Spain. The flight was intended as a general check of the aircraft following its annual engine and airframe maintenance review. The crew consisted of two pilots, both holding private pilot licenses.
After completing engine warm-up and refueling the aircraft to three-quarters capacity, the crew departed from runway 26. The weather conditions were favorable, with good visibility, no wind, and a temperature of 25 °C. The engine operated normally during the takeoff roll and the initial phase of the climb. However, upon reaching approximately 300 feet above the ground and retracting the flaps according to procedure, the pilot experienced engine sputtering and a rapid loss of power.
In an attempt to return to the airfield, the pilot initiated a 180-degree right turn. During this maneuver, the aircraft lost significant altitude. The pilot attempted to stabilize the aircraft for an immediate landing outside the runway. The aircraft impacted the ground 200 meters from the centerline of runway 08 with a nose-down attitude and a left bank. The impact caused significant damage to the landing gear, the nose, the forward fuselage, and the wooden propeller, which suffered breakage of both blades. The two crew members sustained serious and minor injuries but were able to evacuate the aircraft independently.
The investigation
The CIAIAC examined the engine, the fuel system, and the aircraft's weight and balance. The investigation confirmed that the aircraft's estimated takeoff weight was approximately 545 kg, very close to its maximum authorized takeoff weight of 550 kg.
Detailed inspections of the ROTAX 912S engine revealed that the spark plugs, magnetos, and carburetors were in good condition. Bench tests performed on the engine showed it was capable of supplying power without anomalies. However, investigators discovered that the fuel drainage system was configured incorrectly. Instead of draining excess fuel back into the tank as specified by the manufacturer, the drainage line from the fuel manifold to the carburetors was connected to the inlet of the mechanical fuel pump. This configuration created a risk of a vapour lock.
Findings
- The aircraft was operating at a weight near its maximum allowable limit, which may have reduced acceleration capabilities during the climb.
- Retracting the flaps increased the stall speed, and the aircraft's airspeed likely approached this critical threshold during the power loss.
- The improper configuration of the fuel drainage line allowed for the potential formation of a vapor lock in the fuel pump suction area.
- The introduction of warmer fuel into the system during the recent refueling process may have contributed to the formation of fuel vapors, causing the temporary engine sputtering.