History of the flight
The aircraft, a Yak-50 (registration G-IIYK, single Ivchenko Vedeneyev M-14P piston engine), landed on Runway 23 at Lee-on-Solent, Hampshire on 4 September 2007 at 1100 hrs. After clearing the runway, the pilot taxied to park on a tarmac area between a fuel bowser behind a low wall and a hangar. The normal parking area was being mowed, so the pilot chose this location. The engine was running at normal idle (45% rpm). The pilot waited for air pressure to build, as the long taxi with several brake applications had reduced pressure to 2.5 bar.
Accident sequence
The pilot noted slow air recharge and, while holding brakes, closed the cockpit ventilation air valve to allow faster recharging, as high ambient temperatures made it difficult to keep the air-cooled engine below 160°C. Once pressure reached 4 bar, he opened the valve and performed a standard engine run-up at 65% rpm; the brakes held. He then released brakes to apply left rudder and added a trickle of power, operating the brake lever for differential steering to turn 180° before shutdown. The aircraft began to turn but then continued straight ahead. The pilot pumped the brake lever without effect and noticed forward movement despite the throttle being closed. He reached down to close the cockpit air valve to build brake pressure, still holding the brake lever. The throttle remained at idle. Realizing he was moving towards the low wall, he decided to shut down the engine. As he moved his hand from the air switch to the magneto switch, his sleeve caught the throttle, inadvertently applying full power. The aircraft accelerated, the landing gear passed through a gap in the wall, wings mounted the wall, and the aircraft struck the cab of the fuel bowser. The propeller hit the windscreen. The pilot isolated fuel and shut down before exiting uninjured.
Pilot's report
In a comprehensive report, the pilot considered the cause to be the inadvertent power increase from catching the throttle in his sleeve. He concluded that a possible air leak in the landing gear air system may have caused the depletion of air pressure more quickly than usual, leading to loss of braking effectiveness.