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Adverse Weather
• close all window shades on the sun–exposed side of the passenger
cabin
Brake temperature levels may be reached which can cause the wheel fuse plugs to
melt and deflate the tires. Consider the following actions:
• be aware of brake temperature buildup when operating a series of
short flight sectors. The energy absorbed by the brakes from each
landing is cumulative
• extending the landing gear early during the approach provides
additional cooling for tires and brakes
• in–flight cooling time can be determined from the “Brake Cooling
Schedule” in the Performance–In flight section
Engine Operation in Heavy Rain or Hail
If heavy rain or hail encountered or anticipated:
Continuous Ignition switch ........................................................... ON
Provides flameout protection and maintains a minimum thrust setting
of approach idle. Confirm CON IGNITION memo message is
displayed.
During descent:
Autothrottles ................................................................ Disconnect
Note: In heavy precipitation, engine parameter fluctuations may
occur, particularly a noticeable drop in EGT. Engine
parameters will return to normal immediately upon leaving
the area of heavy precipitation.
Turbulence
During flight in light to moderate turbulence, the autopilot and/or autothrottle may
remain engaged unless performance is objectionable. Increased thrust lever
activity can be expected when encountering wind, temperature, and large pressure
changes. Short–time airspeed excursions of 10 to 15 knots can be expected.
Passenger Signs switches ................................................................... ON
Advise passengers to fasten seat belts prior to entering areas of forecast or
suspected turbulence. Instruct flight attendants to check all passengers'
seat belts are fastened.
Continuous Ignition switch ................................................................ ON
April 01, 2001
747 Operations Manual
Supplementary Procedures -
Adverse Weather
Copyright © The Boeing Company. See title page for details.
D6-30151-425 SP.16.9
Severe Turbulence
The turbulent air penetration speed of 290-310 KIAS or .82-.85 Mach provides
ample protection from stall and high speed buffet, while also providing protection
from exceeding the structural limit.
Flight test data substantiates important benfits are obtained from the use of the
yaw dampers during turbulence penetration. Excursions in sideslip and roll are
minimized and, even though the rudder control may be more active, the structural
loads imposed on the vertical tail are considerably reduced.
The recommended procedures for flight in severe turbulence are summarized
below.
Climb and Cruise
After takeoff and when established in a clean climb configuration, the autoflight
system is recommended for flight through turbulence. To reduce pitch changes as
the AFDS attempts to fly speed with elevators, climb and descend using vertical
speed (speed on thrust) and cruise using altitude hold.
In extreme turbulence, it may be necessary to disconnect the autothrottles. With
autothrottles disconnected, the FMC generates a target thrust setting for cruise
which is displayed on EICAS. Set thrust at or slightly above the target thrust
indicator. Change thrust setting only if required to reverse an unacceptable speed
trend.
Descent
If severe turbulence is encountered at altitudes below 15,000 feet and the gross
weight is less than the maximum landing weight, the airplane may be slowed to
250 KIAS in the clean configuration. Adequate stall margin exists under these
conditions.
Delay flap extension in an area of known turbulence as long as possible because
the airplane can withstand higher gust loads in the clean configuration. Diversion
to another airfield is the best policy if severe turbulence persists in the area.
Manual Flight in Severe Turbulence
If manual flight in severe turbulence becomes necessary, trim the airplane for
penetration speed, then do not change stabilizer position. Control the airplane
pitch attitude with the elevators using the attitude indicator as the primary
instrument. In extreme drafts, large attiude changes may occur. Do not make
sudden large control inputs. Corrective actions to regain the desired attitude
should be smooth and deliberate. Altitude variations are likely in severe
turbulence and should be allowed to occur if terrain clearance is adequate. Control
airplane attitude first, then make corrections for airspeed, altitude, and heading.
April 01, 2001
　
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