Accident Overview
On the morning of 17 October 2007, a Britten Norman "Islander" aircraft, registration G-CHES, flew over parts of the Sierra Morena and northern Seville province. Its mission was to scout flight fields for future operations. The day's flight aimed to land at a temporary runway near Guadalcanal, a town in Seville province on the border with Badajoz province. This runway, used by agricultural aircraft, lay about five kilometers southwest of the town. However, the pilot mistakenly landed at another temporary field, Los Tomillares, located on a ranch halfway between the town and the intended runway. The strip at Los Tomillares was considerably shorter, measuring only 400 m in length. The pilot landed normally but needed assistance to depart from the short strip.
Post-Landing Actions and Refueling
To enable departure, the pilot telephoned for help. A pilot experienced with the Islander type arrived early in the afternoon and joined as a crew advisor. Two other persons on the ground assisted with refueling, bringing 250 liters of AV100LL fuel in 50-liter plastic drums. The empty drums were placed inside the aircraft, as there was no refueling service at the strip. Both pilots walked the length of the field to check its condition and dimensions, determining length by counting steps and assessing the gradient. The surface was uncompacted dirt, but they calculated it sufficient for takeoff. They decided to depart toward the southeast to use a favorable negative slope. Their plan was to take off on a SE heading, turn 90° right, fly south until aligned with the Guadalcanal runway, then land on a NW course. They postponed the operation until late in the afternoon, before sunset, to avoid glare from the setting sun while landing at Guadalcanal.
Takeoff and Engine Incident
At approximately 19:30, half an hour prior to sunset, the pilot in command performed the pre-flight check and dismissed the ground assistants, who left before takeoff. The aircraft headed to the runway threshold and began its takeoff. It gained speed and became airborne before reaching the opposite threshold. Shortly after becoming airborne, the right engine started to fail partially, causing the aircraft to yaw hard to the right. The pilot in command, seated in the left seat, was flying. According to the accompanying pilot in the right-hand seat, when the engine failed, the pilot asked him to take the flight controls while he attempted to restore power to the right engine. After lowering the nose, they started to descend slightly and corrected the right yaw by applying left rudder. They had nearly regained directional control when the right engine suddenly ran at full power again. This caused the aircraft to veer left toward higher ground. They were unable to avoid impact.
Impact and Damage
The aircraft's left wingtip impacted first, hitting bushes on the hillside. A few meters later, the left gear wheel made contact. After crossing a small river bed, the left wing and forward fuselage impacted. The airplane came to a stop after traveling along the ground for a few meters. The impact site was on the runway centerline extension, approximately 400 m from the southeast threshold they had overflown seconds earlier during takeoff. The aircraft was seriously damaged and essentially destroyed. There was no fire after the impact.
Official Findings
The official investigation determined that the fault and abnormal operation of the right engine was probably caused by water in the fuel. This water could have come from condensation inside the tanks that was not properly drained during servicing, or from the jugs used to transport fuel prior to refueling at the field. The subsequent loss of lateral control and ability to climb was probably the result of an oscillating condition: the high asymmetric drag from the stationary propeller and counteracting rudder forces were suddenly replaced by high symmetric thrust with the left rudder pedal still fully depressed.