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manual autopilot controls.
· Monitor pitch trim activity and be prepared to disengage if sustained
trimming occurs.
FMC
Note: The FMC will provide a recommended thrust setting and airspeed for
turbulence penetration.
The most important objective is to obtain an initial thrust setting close to the
correct one. Once the proper thrust setting for the recommended penetration
speed is achieved, it is undesirable to make thrust changes during severe
turbulence. Large variations in airspeed and altitude can occur in severe
turbulence.
Airspeed
The maximum turbulent airspeed is 280 KIAS or >>@ Mach .73,
BCD Mach .76 whichever is lower. Below 15,000 feet, a turbulent
airspeed of 250 KIAS may be used if the aircraft gross weight is less than the
maximum landing weight. These speeds should be maintained as they provide
the optimum tradeoff between buffet margin and structural loading. Slower
speeds reduce the buffet margin, increase drag, and increase the out-of-trim
condition due to fluctuations in airspeed. Lower speeds also increase the
potential for turbulence to cause an extreme, unrecoverable attitude.
Sec. 3 Page 320
Rev. 11/15/02 #41 Continental
737
Flight Manual
Sizable and rapid airspeed variations will likely occur depending on the severity
of the turbulence but it is considered highly undesirable to chase airspeed either
with elevator or throttle manipulations. Moderate variations, either above or
below, are of minor consequence since some of the fluctuation of the
instruments is a result of the turbulence itself and does not represent a real
change in the aircraft’s speed or altitude.
Attitude
The natural stability of the aircraft will work in a direction to minimize the loads
imposed by turbulence. The pilot should rely on this natural stability and not
become too greatly concerned about pitch attitude variations. Rapid and large
aileron control inputs are permissible to hold the wings level, but pitch attitude
must be controlled using only small to moderate elevator control inputs to avoid
overstressing aircraft structure. Elevator control should be applied smoothly in
a direction to resist motions away from the desired attitude, and the elevator
should be returned to neutral when the aircraft is progressing toward the desired
attitude.
Pitch attitude should be controlled solely with the elevator, never with stabilizer
trim. An updraft or downdraft, which might tempt the pilot to change trim, can
be expected to reverse itself in the next few seconds. If trim has been applied to
counter the first draft, the second draft (which will likely be in the opposite
direction) will exaggerate the out-of-trim condition. It is therefore considered
desirable to leave the stabilizer trim alone in severe turbulence.
Thrust
Note: Use speedbrakes to slow if necessary. Adjust throttles only as
necessary to avoid excessive airspeed variations. Use smooth power
changes and maintain thrust as high as practicable. Do not chase
airspeed.
Large variations in airspeed and altitude are almost certain to occur in severe
turbulence. Set thrust to maintain the recommended penetration speed in level
flight and minimize thrust changes.
737
Flight Manual Continental
Sec. 3 Page 321
Rev. 11/15/02 #41
Altitude
Large variations in altitude are almost certain to occur in severe turbulence due
to high velocity updrafts and downdrafts. Report the turbulence to ATC and
advise them of the potential for altitude deviations. Altitude control is
secondary to the need to avoid excessive structural loads or reduced buffet
margin. Altitude should be allowed to vary as required to avoid excessive
control input and maintain altitude. Descend as necessary to improve buffet
margin.
Turbulence encounters at high altitudes (or during high-speed cruise at
intermediate altitudes) may produce high speed buffeting. High speed buffet,
while disconcerting, is not as hazardous as overcontrolling the aircraft. Such an
occurrence should not be misinterpreted as a low speed stall, since an
unaccompanying rapid pushover for recovery might aggravate the buffet
situation by increasing the airspeed. Severe turbulence encounters at high
altitude have caused load factors as high as 2.5 G-forces. If the recommended
attitude control procedures are followed, excessive load factors need not be
imposed. The potential for high-speed buffeting in severe turbulence is greater
at higher altitudes. Climbing to avoid an area of expected severe turbulence
increases the chance of buffeting if turbulent region cannot be completely
topped.
Structural
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