Amateur-built TWIN 503SL N426MT accident near Torrance, California

Probable cause

The passenger’s inadvertent activation of the engine throttle.

NTSB analysis

The owner/pilot said that the pilot-rated passenger, who was seated in the front seat, had been shown the function of the steering bar, the pedals, the brake, and the throttle. After engine start and while performing the pre-taxi checklist, the steering control bar was tied to the glider's frame tube with a bungee cord. The pilot performed a brake check from the rear seat and then asked the passenger to perform the brake check from the front seat. The glider foot controls are similar to airplane controls, except when the top of the left pedal is depressed it activates the nosewheel brake. When the top of the right pedal is depressed it activates the throttle instead of activating the brake. After the pilot asked the passenger to perform the brake check, the glider engine accelerated to full power and the glider became airborne. Because the control bar was tied to the main frame of the glider the pilot was unable to attain control before the glider stalled. The owner/pilot indicated that the glider did not have a mechanical malfunction or failure.

Text from the NTSB. Open the NTSB docket for WPR09LA130 for the full record.