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conditions involves many conservative practices, these practices have never been
intended to validate operations of unlimited duration in severe icing conditions.
The safest course of action is to avoid prolonged operation in moderate to severe
icing conditions.
Operations of the 767 in icing conditions have resulted in rare occurrences of
elevated airframe buffet upon selection of landing flaps during the approach.
Testing has shown that ice accumulation on the flaps may cause an increase in
airframe buffet levels under some operating conditions. The airframe buffet can
be described as having characteristics similar to buffet associated with speedbrake
extension at flaps 20 or greater. The buffet becomes more noticeable with
increasing flap deflection and at forward centers of gravity. In addition, ice
accumulation on extended trailing-edge flaps may result in decreased lift and
increased stall speeds at landing flaps. These effects are dependent on the amount
of ice adhering to the flaps. Normal operating procedures for flight in icing
conditions accommodate these performance effects. Performance adjustments are
provided in the AFM for operations with ice accumulation on the thermally
unprotected wing and tail surfaces. No additional changes to operating procedures
are required due to ice accumulation on extended trailing-edge flaps. In order to
minimize the impact of ice accumulation on airplane performance and ride quality,
avoid holding with trailing-edge flaps extended when in icing conditions.
Training Flights
Multiple approaches and/or touch and go landings in icing conditions may result
in significant ice accumulations beyond those experienced during typical revenue
flights. This may result in fan blade damage as a result of ice accumulation on
unheated surfaces shedding into the engines.
October 31, 2004
767 Flight Crew Training Manual
General Information
Copyright © The Boeing Company. See title page for details.
1.28 FCT 767 (TM)
Recommended Rudder Trim Technique
This section describes two techniques for properly trimming the rudder. It is
assumed that the airplane is properly rigged and in normal cruise. The primary
technique uses rudder trim only to level the control wheel and is an acceptable and
effective method for trimming the airplane. It is approximately equal to a
minimum drag condition. This technique is usable for normal as well as many
non-normal conditions. For some non-normal conditions, such as engine failure,
this technique is the preferred method and provides near minimum drag.
The alternate technique may provide a more accurate trim condition when the roll
is caused by a roll imbalance. In addition, this technique outlines the steps to be
taken if the primary trim technique results in an unacceptable bank angle or
excessive rudder trim. The alternate technique uses both rudder and aileron trim
to neutralize a rolling condition using the bank pointer as reference.
Note: Large trim requirements should be documented for maintenance. (Refer to
the maintenance manual for guidance.)
Drag Factors Due to Trim Technique
If the control wheel is displaced to the point of spoiler deflection a significant
increase in aerodynamic drag results. Additionally, any rigging deviation that
results in early spoiler actuation causes a significant increase in drag per unit of
trim. These conditions result in increased fuel consumption. Small out of trim
conditions affect fuel flow by less than 1%, if no spoilers are deflected.
Note: Aileron trim may be required for significant fuel imbalance, airplane
damage, or flight control system malfunctions.
Primary Rudder Trim Technique
It is recommended that the autopilot remain engaged while accomplishing the
primary rudder trim technique (using rudder trim only). After completing this
technique, if the autopilot is disconnected, the airplane should maintain a constant
heading.
The following steps define the primary rudder trim technique:
• set symmetrical thrust
• balance fuel if required
October 31, 2004
767 Flight Crew Training Manual
General Information
Copyright © The Boeing Company. See title page for details.
FCT 767 (TM) 1.29
• ensure the autopilot is engaged in HDG SEL or HDG HOLD and
stabilized for at least 30 seconds
• trim the rudder in the direction corresponding to the down (low) side of
the control wheel until the control wheel indicates level. The indices on
top of the control wheel should be used to ensure a level wheel condition.
The airplane is properly trimmed when the control wheel is level, (zero
index). As speed, gross weight, or altitude change, trim requirements may
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767机组训练手册Flight Crew Training Manual (FCTM)767(20)
