What happened
On November 21, 2004, a De Havilland Canada DHC-1 Chipmunk, registration G-OACP, was performing a training flight at the Cascais Municipal Aerodrome (Tires) in Portugal. The flight was intended to familiarize an instructor with operating the aircraft from the rear seat, with a passenger seated in the front to simulate the weight and visibility obstruction of a student.
The flight involved a series of touch-and-go maneuvers. During one such maneuver, the pilot applied power abruptly to initiate the takeoff phase. This sudden increase in power caused the aircraft to yaw sharply to the left due to torque effects. Although the pilot attempted to correct the deviation, the aircraft drifted off the left side of runway 35, crossed a drainage ditch, and struck a manhole cover. The impact caused the right main landing gear to break off, leading the aircraft to capsize and come to rest in the ditch. Both occupants escaped the aircraft without injury, though the aircraft sustained significant damage to its wings, stabilizers, propeller, and landing gear.
The investigation
The GPIAAF investigation examined the aircraft's mechanical history and the operational conditions at the time of the accident. It was noted that while the aircraft was originally built with a Gipsy Major engine, it had been re-motorized with a more powerful 180 Hp Lycoming engine. This modification changed the propeller rotation direction and altered the torque characteristics, resulting in specific operational limitations regarding crosswind components.
The investigators also examined the airfield infrastructure, specifically the drainage ditch located west of the runway. The investigation noted that this ditch had been a factor in previous runway excursions at the aerodrome, including a Cessna 152 accident earlier that same year.
Findings
- The primary cause of the accident was loss of control during the takeoff phase due to deficient piloting technique.
- The pilot applied power too abruptly during a touch-and-go maneuver, triggering a sudden yaw caused by the engine's torque effect.
- The aircraft's recent re-motorization to a 180 Hp engine had created an imbalance in torque compensation, making the aircraft more susceptible to directional deviations during high-power applications.
- The presence of the drainage ditch acted as a significant hazard, as the impact with the manhole cover directly caused the aircraft to overturn.
- Meteorological conditions were favorable, with good visibility and calm winds, and did not contribute to the event.