NTSB Probable Cause Reports Throttle Was Activated By
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
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.
In his written report, the pilot described the systems of the
weight-shift-control power glider, which he referred to as a
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
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."