737 Flight Crew Training Manual
Flap Extension using the Alternate System
When extending the flaps using the alternate system, the recommended method for setting command speed differs from the method used during normal flap extension. Since the flaps extend more slowly when using the alternate system, it is recommended that the crew delay setting the new command speed until the flaps reach the selected position. This method may prevent the crew from inadvertently getting into a low airspeed condition if attention to airspeed is diverted while accomplishing other duties.
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.
Copyright . The Boeing Company. See title page for details.
8.14 FCT 737 (TM) October 31, 2006
737 Flight Crew Training Manual
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.
For those controls without override features, limited flight control surface
deflection occurs when considerable force is applied to the flight control. This
response is due to cable stretch and structural bending. This response may be
sufficient for airplane control and landing.
737-300 - 737-500
Note: There is an override feature that allows control of the ailerons or spoilers.
737-600 - 737-900
Note: There is an override feature that allows control of the ailerons or spoilers.
There is also an override feature that allows control of the elevator in the
event of a control column jam.
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.
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