SUBJECT Simulator training for technical crew 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.