NTSB Probable Cause Reports Throttle Was Activated By Accident

The NTSB has released a probable cause report in a fatal accident involving a weight-shift power glider in Torrance, CA in February of 2009. The probable cause was shown to be the aircraft's passenger’s "inadvertent activation of the engine throttle."

In its report, the board said that during a pre-flight briefing, the owner/pilot, who survived the accident, had shown the pilot-rated passenger, who was seated in the front seat, 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. However, since the glider had not completed the pre-taxi checklist and the control bar was still bungee-tied to the down tube, the pilot was unable to maneuver the wing. The glider climbed to approximately 100 feet, stalled, and descended back to the ground impacting nose first. The glider hit the ground in the middle of the airport, between the two runways.

PERSONNEL INFORMATION
The owner/pilot, holds multiple ratings, which includes a weight-shift-control flight instructor rating, with night flying authorization. The purpose of the flight was to maintain his night flight qualification.

The pilot rated passenger in the front seat was not receiving instruction, he had never before flown in the accident glider before, and was along for the flight as a passenger.

AIRCRAFT INFORMATION
In his written report, the pilot described the systems of the weight-shift-control power glider, which he referred to as a “trike.”

The accident glider is steered by two foot pedals in front of each pilot. The foot controls are similar to airplane controls, except when the top of the left pedal is depressed it activates the nose wheel brake. When the top of the right pedal is depressed, it activates the throttle, instead of activating the brake.

The glider is controlled in pitch and roll by a "control bar" in front of the front-seated pilot, which maneuvers a large hang-glider wing. The instructor in the back has "extension bars" that allow him to maneuver the control bar. When the control bar is bungee-tied to the down tube the wing is "locked," comparable to the control locks on the ailerons, rudder, and elevator of an airplane.

WRECKAGE AND IMPACT INFORMATION
The Federal Aviation Administration (FAA) accident coordinator inspected the wreckage at the accident scene prior to the recovery and verified control continuity to all of the flight controls and the throttle linkage. A bungee cord was noted to be located near the control bar and near the airframe down tube.

MEDICAL AND PATHOLOGICAL INFORMATION
The Los Angeles County Coroner completed an autopsy on the passenger. The cause of death was determined to be a result of blunt force trauma. Analysis of the specimens for the passenger contained no findings for volatiles or tested drugs. They did not perform tests for carbon monoxide or cyanide.

The NTSB reports that in the pilot’s written statement he said the following items are highly recommended to prevent such an accident from occurring again:

• Trike (power glider) pilots should be aware that the engine could experience uncommanded full power at any time after the engine is running. This could occur during taxi, during the magneto check in the run-up area, or even after landing.
• Before the engine is started, and at all times thereafter, the bungee-tie should be removed from the control bar/down tube. In other words, from the time that the engine is started the trike pilot should be able to fully manipulate the control bar without interference from the bungee so that he can immediately start flying the trike in the event of an uncommanded full power causes the trike to unexpectedly take off and become airborne.
• Both the front and rear pilots should have immediate and unimpeded access to a "kill switch” that would stop the engine in the event of an uncommanded power increase.

According to FAA Advisory Circular AC 20-27F, Certification and Operation of Amateur-Built Aircraft, "Amateur builders are free to develop their own designs or build from existing designs. We do not approve these designs and it would be impractical to develop design standards for the wide variety of design configurations, created by designers, kit manufacturers, and amateur builders."

FMI: www.ntsb.gov