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8.12 FCT 777/787 Preliminary (TM)
Jammed or Restricted Flight Controls
Although rare, jamming of the flight control system has occurred on commercial
airplanes. A jammed flight control can result from ice accumulation due to water
leaks onto cables or components, dirt accumulation, component failure such as
cable break or worn parts, improper lubrication, or foreign objects.
A flight control jam may be difficult to recognize, especially in a properly
trimmed airplane. A jam in the pitch axis may be more difficult to recognize than
a jam in other axes. In the case of the elevator, the jammed control can be masked
by trim. Some indications of a jam are:
• unexplained autopilot disconnect
• autopilot that cannot be engaged
• undershoot or overshoot of an altitude during autopilot level-off
• higher than normal control forces required during speed or configuration
changes.
If any jammed flight control condition exists, both pilots should apply force to try
to either clear the jam or activate the override feature. There should be no concern
about damaging the flight control mechanism by applying too much force to either
clear a jammed flight control or activate an override feature. Maximum force may
result in some flight control surface movement with a jammed flight control. If the
jam clears, both pilot’s flight controls are available.
Note: If a control is jammed due to ice accumulation, the jam may clear when
moving to a warmer temperature.
Some flight controls are linked together through override features. If the jam does
not clear, activation of an override feature allows a flight control surface to be
moved independent of the jammed control. Applying force to the non-jammed
flight control activates the override feature. When enough force is applied, the
jammed control is overridden allowing the non-jammed control to operate. To
identify the non-jammed flight control, apply force to each flight control
individually. The flight control that results in the greatest airplane control is the
non-jammed control.
Note: The pilot of the non-jammed control should be the pilot flying for the
remainder of the flight.
The non-jammed control requires a normal force, plus an additional override force
to move the flight control surface. For example, if a force of 10 lbs (4 kgs) is
normally needed to move the surface, and 50 lbs (23 kgs) of force is needed to
activate the override, a total force of 60 lbs (27 kgs) is needed to move the control
surface while in override. Response is slower than normal with a jammed flight
control; however, sufficient response is available for airplane control and landing.
October 31, 2006
777/787 Flight Crew Training Manual
Non-Normal Operations
Copyright © The Boeing Company. See title page for details.
FCT 777/787 Preliminary (TM) 8.13
Individual flight control surfaces that do not respond correctly to pilot or autopilot
inputs may cause either a FLIGHT CONTROLS or SPOILERS EICAS message
to display. Because the flight control surfaces are electronically controlled, an
individual flight control surface jam will not result in restricted movement of the
control wheel or column, except to a limited extent in the case of spoilers 4 and 11.
777-200 - 777-300ER
Note: There are override features in the flight deck controls for the control wheel,
control column, and mechanical spoiler pair.
787-8
Note: There are override features in the flight deck controls for the control wheel,
control column, and rudder pedals.
Trim Inputs
If a jammed flight control condition exists, use manual inputs from other control
surfaces to counter pressures and maintain a neutral flight control condition. The
following table provides trim inputs that may be used to counter jammed flight
control conditions.
Approach and Landing
Attempt to select a runway with minimum crosswind. Complete approach
preparations early. Recheck flight control surface operation prior to landing to
determine if the malfunction still exists. Do not make abrupt thrust, speedbrake,
or configuration changes. Make small bank angle changes. On final approach, do
not reduce thrust to idle until after touchdown. Asymmetrical braking and
asymmetrical thrust reverser deployment may aid directional control on the
runway.
Note: In the event of an elevator jam, control forces will be significantly greater
than normal and control response will be slower than normal to flare the
airplane.
Jammed Control Surface Manual Trim Inputs
Elevator Stabilizer (Direct mode
only with PFC disconnect
switch activated)
Aileron Rudder*
Rudder Aileron*
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787机组训练手册Flight Crew Training Manual 787(127)
