TURBULENCE AIR PENETRATION
**** Hidden Message ***** GENERAL· The turbulent air penetration speed is:
- B737 Classics……….. 280 KIAS /.73 Mach
- B737 NG …………….. 280 KIAS /.76 Mach
· The turbulent air penetration speed was selected to provide low/high speed maneuver margins in
severe turbulent air. Below 10,000 feet, a speed between 240 and 250 knots provides adequate
buffet margin.
· Severe turbulence should be avoided if at all possible. If severe turbulence cannot be avoided,
an increased buffet margin is recommended. This can be obtained by descending approximately
4,000 feet below optimum attitude.
· If the autopilot is engaged, leave it engaged unless airspeed, altitude or attitude deviations
require use of manual control.
· The autothrottle should be off in severe flight, maintain wings level and smoothly control attitude.
· Use the attitude indicator as the primary instrument.
· In extreme vertical wind currents, large altitude changes may occur.
· Do not use sudden or large control inputs. After establishing the trim setting for penetration
speed, do not change pitch trim.
· Allow attitude and airspeed to vary and maintain attitude. However, do not allow the airspeed to
decrease and remain below the turbulent air penetration speed as buffet margin will be reduced.
· Maneuver at bank angles below those normally used.
· Set thrust for penetration speed and avoid large thrust changes.
· Continuous ignition (FLT position) should be on.
· Flap extension in an area of known turbulence should be delayed as long as possible because
the airplane can withstand higher gust loads in the clean configuration.
· Normally, no changes to cruise altitude or airspeed are required when encountering moderate
turbulence. If operating at cruise thrust limits, it may be difficult to maintain cruise speed.
Editor : Copyright Ó Smartcockpit.com / Ludovic ANDRE version 01
Smartcockpit.com BOEING 737 BRIEFINGS Page 2
TURBULENCE PROCEDURE
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 changes and large pressure changes. Short-time airspeed
excursions of 10 to 15 knots can be expected.
PASSENGER SIGNS ..………..….. ON
Advise passengers to fasten seat belts prior to entering areas of reported or anticipated turbulence. Instruct
flight attendants to check that all passengers' seat belts are fastened.
Severe Turbulence
AUTOTHROTTLE…………DISENGAGE
AUTOPILOT……………………….. CWS
A/P status annunciators display CWS for pitch and roll.
Note: If sustained trimming occurs, disengage the autopilot.
ENGINE START SWITCHES …….. FLT
THRUST ......................................... SET
Set thrust as required for the phase of flight. Change thrust setting only if required to modify an
unacceptable speed trend.
PHASE OF FLIGHT AIRSPEED
CLIMB · B737 Classics……….. 280 KIAS /.73 Mach
· B737 NG …………….. 280 KIAS /.76 Mach
CRUISE
· Use FMC recommended thrust settings.
· If the FMC is inoperative, refer to the Unreliable Airspeed
page in the Performance-Inflight section for approximate N1
settings that maintain near optimum penetration airspeed.
DESCENT
· B737 Classics………...73 Mach / 280 / 250 KIAS
· B737 NG ……………...76 Mach / 280 / 250 KIAS
· If severe turbulence is encountered at altitudes below 15,000
feet and the airplane gross weight is less than the maximum
landing weight, the airplane may be slowed to 250 knots in
the clean configuration.
Note: If an approach must be made into an area of severe turbulence, delay flap extension as
long as possible. The airplane can withstand higher gust loads in the clean configuration. hhhhhhhhhhhhhhhhhhhhhhh
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