SUBJECT
Simulator training for technical crews to equip them to handle
jammed ailerons in flight on Boeing aircraft.
OCCURRENCE SUMMARY
Shortly after departing from runway 34L at Sydney, the pilot of a
Boeing 747 advised the departures controller that he could only
comply with left turns, and that he needed to jettison fuel and
return to the airfield. A distress phase was declared and the
aircraft was vectored left to an area over water where fuel was
dumped. The aircraft was subsequently vectored to the centreline of
runway 34L and landed safely.
The subsequent investigation found that a plastic aileron cable
guard had broken and jammed the aileron cables where they run
vertically up the left sidewall of the aircraft. The pilot reported
that he was unable to input any right aileron control and it
appeared to be jammed.
ANALYSIS
The roll control surfaces on Boeing aircraft consist of
hydraulically-powered inboard and outboard ailerons (and spoilers)
which are normally controlled by rotating either control wheel. The
aileron cable control systems are constructed in two separate sets,
linked at the control wheels.
The control wheels are connected through an override mechanism
which allows either wheel to move independently if the aileron
control system connected to the other wheel jams and a significant
manual force is applied to the free wheel. Roll control is then
available through the ailerons on the wing corresponding to the
free wheel.
The pilot in command of the above mentioned aircraft advised that
after the aircraft had been landed, he was present when repairs
were carried out and was surprised at the aileron breakout force
required to override a jammed system. Ground training he had
received covered aileron breakout (override) procedures but he
believed it would be beneficial to have it physically demonstrated
during simulator training in case of such an emergency.
Discussions with other technical crews revealed that, while they
were aware of the system, they were generally not aware of the
physical forces required to break out the aileron control system in
the event of an aileron system jam.
The Boeing Company does not recommend activating the breakout
feature of the aileron control system on a regular basis due to
possible stretching of aileron cables and excessive wear to a
system that is installed for emergency use only.
It has been reported that flight simulators in use by operators of
Boeing aircraft in Australia can be programmed to enable
demonstration of aileron control breakout forces. If the simulators
are programmed correctly, all technical crews can be safely exposed
to this aspect during simulator training.
The Boeing Commercial Airplane Company advised that Boeing B737,
B747, B757 and B767 aircraft are all fitted with similar emergency
aileron override and breakout systems.
SAFETY DEFICIENCY
The aircraft is designed to be flown from either control position
should one side become jammed. The pilot was aware of this design
feature but was not aware of the amount of force required to
activate the breakout system.
Technical crews are instructed on this control feature during
ground training but are not physically exposed to the forces
required, either on an aircraft or in a simulator.
