Autothrottle (A/T) ARM Switch
ARM – Arms A/T for engagement. Magnetically held at ARM. A/T engages automatically when following AFDS modes are engaged:
.
LVL CHG

.
ALT ACQ

.
V/S

.
VNAV

.
ALT HOLD

.
G/S capture

.
TO/GA.

The indicator light illuminates green when A/T ARM switch is in the ARM
position.
OFF – disengages A/T and prevents A/T engagement.

Changeover (C/O) Switch
Push –
.
changes IAS/MACH display between IAS and MACH

.
automatic changeover occurs at approximately FL260.

MCP Speed Condition Symbols
Overspeed or underspeed limiting symbol appears when commanded speed cannot be reached.
Underspeed limiting (flashing character “A”) – minimum speed
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Automatic Flight -Controls and Indicators 737 Flight Crew Operations Manual

Overspeed limiting (flashing character “8”) –
.
Vmo or Mmo limit

.
landing gear limit

.
flap limit.

IAS/MACH Display
Displays speed selected by IAS/MACH selector
.
display is blank when:

.
VNAV mode engaged

.
A/T engaged in FMC SPD mode

.
during 2 engine AFDS go–around

.
displays 100 knots when power is first applied

.
display range is:

.
100 KIAS – Vmo in 1 knot increments

.
.60M – Mmo in .01M increments.

N1 Switch
Push – (light not illuminated)
.  
engages A/T in N1 mode if compatible with AFDS modes already
engaged

.
illuminates N1 switch light

.
annunciates N1 autothrottle mode.

Push – (light illuminated)
.
deselects N1 mode and extinguishes switch light

.
engages autothrottles in ARM mode.

N1 Mode
.  
A/T maintains thrust at N1 limit selected from FMC CDU. N1 mode engaged manually by pushing N1 switch if N1 mode is compatible with existing AFDS modes. N1 mode engages automatically when:

.  
engaging LVL CHG in climb (except during inhibit period for 2 1/2 minutes after lift-off)

.
engaging VNAV in climb.

SPEED Switch
Push – (light not illuminated)
.
engages A/T in SPEED mode if compatible with engaged AFDS modes

.
illuminates SPEED switch light

.
annunciates MCP SPD autothrottle mode

.
maintains speed in MCP IAS/MACH display.

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4.10.4   March 28, 2005

Automatic Flight -Controls and Indicators 737 Flight Crew Operations Manual
Push – (light illuminated)
.
deselects speed mode and extinguishes switch light

.
engages A/T in ARM mode.

Speed Mode
Autothrottle holds speed in IAS/MACH display or a performance or limit speed. Speed mode engaged manually by pushing SPEED switch if speed mode is compatible with existing AFDS modes. Speed mode engages automatically when:
.
ALT ACQ engages

.
ALT HOLD engages

.
V/S engages

.
G/S capture occurs.

A/T does not set thrust above displayed N1 limit, however, A/T can exceed N1 value manually set by N1 Manual Set Knob.

IAS/MACH Selector
Rotate –
.
sets speed in IAS/MACH display and positions airspeed cursor

.
selected speed is reference speed for AFDS and A/T

.
not operative when IAS/MACH display is blank.

Speed Intervention (SPD INTV) Switch YD651 - YD655
Push (when VNAV engaged) –
.
IAS/MACH display alternately shows selected IAS/Mach and blanks

.  
when IAS/MACH display is unblanked, FMC speed intervention is
active, FMC target speed is displayed, and IAS/MACH Selector may be
used to set desired speed

.  
when IAS/MACH display is blank, FMC computed target speed is active
and displayed on the airspeed indicator.

Copyright . The Boeing Company. See title page for details.

YA613 - YC154

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4.10.6  June 1, 2005

Automatic Flight -Controls and Indicators 737 Flight Crew Operations Manual

VNAV Switch
Push –
.  
VNAV switch light illuminates
YD651 - YD655