What happened
On 18 April 2003, a Stolp Starduster Too SA300, registration G-BNNA, was conducting a private pleasure flight from Leicester Airport. After climbing to a safe altitude and completing a slow roll, the pilot attempted to reduce power to a cruise setting. During this maneuver, the throttle movement became stiff and eventually jammed. The engine RPM dropped to 1,200, and the pilot found it impossible to increase power further.
Because the aircraft remained within gliding distance of the airfield, the pilot declared an emergency and prepared for a forced landing on the grass Runway 06. During the final approach, the pilot attempted to close the throttle fully to manage the descent, but the mechanism remained stuck. To prevent the aircraft from being too high for the intended runway, the pilot elected to shut down the engine by turning off the magnetos and redirected the aircraft toward Runway 28.
While the landing was completed, a 25-knot crosswind caused the aircraft to ground loop. The impact resulted in no injuries to the pilot or the passenger, but the aircraft sustained a collapsed port undercarriage leg and damage to the underside of the port lower wing.
The investigation
Investigators examined the throttle control system, which utilizes a Bowden cable arrangement. This system consists of an inner cable housed within a flexible outer sheath, supported at intervals by 'P' clips. Following the accident, the pilot inspected the cable route and identified that at least one supporting clip was missing. It was determined that the absence of this clip allowed the outer sheath to kink, which subsequently caused the inner throttle cable to jam.