.
autopilot that cannot be engaged
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undershoot or overshoot of an altitude during autopilot leveloff
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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 independently of the jammed control. Applying force to the non-jammed flight control activates the override feature. When enough force is supplied, 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 aircraft 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 kg) is normally required to move the surface, and 50 lbs (23 kg) of force is required to activate the override, a total force of 60 lbs (27 kg) is required to move the control surface while in override. Response is slower than normal with a jammed flight control; however, sufficient response is available for aircraft 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 aircraft control and landing.
Note: There are override features for the aileron and elevator.
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.
Jammed Control Surface Manual Trim Inputs
Elevator Stabilizer
Aileron Rudder*
Rudder Aileron*
*Asymmetric engine thrust may aid roll and directional control.
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.
Go Around Procedure
If the elevator is known or suspected to be jammed, a go-around should be avoided if at all possible. To execute a go-around with a jammed elevator, smoothly advance throttles while maintaining pitch control with stabilizer and any available elevator. If a go-around is required, the go-around procedure is handled in the same manner as a normal go-around.
Jammed Stabilizer
During flight test certification the worst-case jammed stabilizer condition was evaluated. A satisfactory landing could be accomplished without the use of special configurations or speeds. Adequate flare capability was available at flaps 30 and flaps 20 using normal approach speeds. Therefore, a special flight checklist is not considered necessary.
Unscheduled Stabilizer Trim
Hold control column firmly to maintain desired pitch attitude. If uncommanded trim motion continues, the stabilizer trim commands are interrupted when the control column is displaced in the opposite direction.
Flight Instruments, Displays Airspeed Unreliable
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本文鏈接地址：757 Flight Crew Training Manual 機組訓練手冊(90)
