Auto Throttle

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NBAA 2003

Civil Aviation Flight University of China

Auto ThrottleAuto Throttle

自动油门自动油门

Auto Throttle (A/T)Auto Throttle (A/T)

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A typical A/T system provides automatic thrust control from the start of take-off through climb, cruise descent, approach and go-around or landing.

The A/T system also ensures that the engines operate within the permitted engine limits.

The A/T system has a number of operating modes that can be used from brakes release through to landing.

Auto Throttle (A/T)Auto Throttle (A/T)

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A/T Mode Control PanelA/T Mode Control Panel

Figure 3.15

F /DO N

O F F

A /T A R M

O F F

E P R

S P D

S E L

IA S /M A C H

L N AV

V N AV

F L C H

H D G

A U T O B A N K

H O L D

V E RT S P D

D N

U P

V /S H O L D

A LT

B C R S

L O C

A P P

A /P E N G A G EL C R

C M D C M D C M DF /DO N

O F FD IS E N G A G E

S E LL IM IT

5 2 5

2 0 0 1 4 0 2 3 00+ 1 5 0 0 0

A /T A R M

O F F

E P R

S P D

IN S T RS W IT C H

A LTA L E RT

A /TD IS C

A /T D IS C L ig h t

A u to th ro ttle D ise n g a g e S w itc h es（ B o th S id es）

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F /DO N

O F F

A /T A R M

O F F

E P R

S P D

S E L

IA S /M A C H

L N AV

V N AV

F L C H

H D G

A U T O B A N K

H O L D

V E RT S P D

D N

U P

V /S H O L D

A LT

B C R S

L O C

A P P




S E LL IM IT

5 2 5

2 0 0 1 4 0 2 3 00+ 1 5 0 0 0

A /T A R M

O F F

E P R

S P D

IN S T RS W IT C H

A LTA L E RT

A /TD IS C



A/T ARM switch arms autothrottle for engagement. Autothrottle engages when EPR or SPD switch is pushed, and when V NAV, FL CH or GA modes are active.

EPR switch engages autothrottle to hold reference EPR displayed on EICAS, subject to maximum speed limits.

SPD switch engages autothrottle to hold speed or Mach indicated in IAS/MACH indicator. It cannot be engaged while in the TO thrust mode.

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NBAA 2003



Figure 3.15

F /DO N

O F F

A /T A R M

O F F

E P R

S P D

S E L

IA S /M A C H

L N AV

V N AV

F L C H

H D G

A U T O B A N K

H O L D

V E RT S P D

D N

U P

V /S H O L D

A LT

B C R S

L O C

A P P




S E LL IM IT

5 2 5

2 0 0 1 4 0 2 3 00+ 1 5 0 0 0

A /T A R M

O F F

E P R

S P D

IN S T RS W IT C H

A LTA L E RT

A /TD IS C



A/T DISC light indicates autothrottle is disengaged, either due to malfunction, pushing autothrottle disengage switch, or raising reverse levers to the interlock.

Autothrottle disengage switches disengage the autothrottle. Second push turns off A/T DISC light.

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Figure 3.16

Thrust Mode Control PanelThrust Mode Control Panel

T OG A C L B 1 2

C O N C R Z

T E M P S E L

C lim b T h ru s t D e ra te S w itc h e s

T E M P S E L K n o bT h ru s t M o d e S e le c t S w itc h e s

TAT + 1 2 ¡ ãC + 4 0 ¡ ãCD -T O 2

2 .0

1 .0

1 .5

1 .0

1 .5

2 .0

E P R

1 .4 8 1 .4 81 .4 81 .4 8

To ta l A ir Te m p e ra tu reR e fe re n c e E P R

A ssu m e d Te m p e ra tu reT h ru s t R e fe re n c e M o d e

E P R C o u n te r

E P R P o in te r

E P R B u gL im it E P R （ A m b e r）

Required EPR (or N1) for the A/T EPR mode would be selected on a separate thrust mode control panel . The available thrust modes are:• take-off/go-around (TO/GA) — full power;• climb power (CLB), plus two values of derated climb power;• maximum continuous power (CON); and• cruise power (CRZ).

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Thrust mode select switches select the thrust mode to be used by the thrust management computer for reference EPR limit computation.

The active thrust mode and reference EPR are indicated on EICAS.

With VNAV engaged, manual selection of GA, CLB, and CON is inhibited.


Figure 3.16

T OG A C L B 1 2

C O N C R Z

T E M P S E L



TAT + 1 2 ¡ ãC + 4 0 ¡ ãCD -T O 2

2 .0

1 .0

1 .5

1 .0

1 .5

2 .0

E P R

1 .4 8 1 .4 81 .4 81 .4 8



E P R C o u n te r

E P R P o in te r


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Climb thrust derate switches select either of two fixed percentage derate values for climb thrust computation.

Switch 1 selects approximately 8% derate and switch 2 selects approximately 16%.


Figure 3.16

T OG A C L B 1 2

C O N C R Z

T E M P S E L



TAT + 1 2 ¡ ãC + 4 0 ¡ ãCD -T O 2

2 .0

1 .0

1 .5

1 .0

1 .5

2 .0

E P R

1 .4 8 1 .4 81 .4 81 .4 8



E P R C o u n te r

E P R P o in te r


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TEMP SEL knob selects the assumed temperature for derated take-off thrust.

If an assumed temperature is not selected, the computer uses the higher of TAT or flat rated temperature to compute the take-off limit.

The knob is active only in the take-off mode.


Figure 3.16

T OG A C L B 1 2

C O N C R Z

T E M P S E L



TAT + 1 2 ¡ ãC + 4 0 ¡ ãCD -T O 2

2 .0

1 .0

1 .5

1 .0

1 .5

2 .0

E P R

1 .4 8 1 .4 81 .4 81 .4 8



E P R C o u n te r

E P R P o in te r


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Autothrottle Mode AnnunciationsAutothrottle Mode Annunciations

Autothrottle mode annunciation indicates in green that autothrottle is engaged in the displayed mode.

Possible mode annunciations are EPR, SPD, FL CH, GA, IDLE, TEST and THR-HOLD. Possible limit annunciations are FLAP, ALPHA, SPD LIM. Only one limit mode is displayed at a time.

Figure 3.172 0 2 0

G S L O C C M D

6 0

S P D

A u to th ro ttle M o d e A n n u n c ia tio n A u to th ro ttle L im it A n n u n c ia tio n

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Operation of a Typical Autothrottle SystemOperation of a Typical Autothrottle System

• Reduced Thrust Take-off Mode

An assumed temperature is selected.

The autothrottle is engaged by pressing the EPR switch.

The autothrottle will engage in the TO mode and the throttles will be driven

forward until reduced take-off thrust (assumed temperature) is achieved.

Below 80 kt groundspeed as sensed by the IRS, the throttles are driven

continuously to sustain this EPR.

Above 80 kt groundspeed, electrical power to the throttle drive motor(s) is

withdrawn, and the autothrottle mode changes to THR HOLD.

Any adjustment now made by the pilot will not be countered by the

autothrottle.

After take off, the autothrottle can be re-engaged in an active mode by pressing

the EPR button.

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• Full Power Take-off Mode When conditions do not permit the use of reduced thrust, or if the pilot decides to use maximum thrust, this take-off mode can be engaged by pressing the TO/GA button. This selection overrides any assumed temperature inputs, and the engine is accelerated to the limiting EPR for the ambient conditions. THR HOLD mode and re-engagement of an active mode remain the same.

• Climb Mode The thrust mode control panel offers three values of climb power; (full) climb power, Derate 1 climb power, and Derate 2 climb power, enabling the pilot to select the level of derate most suitable to the conditions of the day.

Derate1 is a reduction of about 8%, while Derate 2 reduces climb power by about16%.

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• Speed Mode

This mode is engaged by selecting an appropriate IAS or Mach in the AFDS

speed setting window and pressing the speed mode control button. Once set, the

A/T will move the power levers as required to maintain the desired speed, within

the boundaries of allowed engine limits.

• Flight Level Change Mode

When the FL CH mode is engaged, the autothrottle will set climb power or

flight idle as required, depending on whether the selected altitude is above or

below the aircraft.

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• Go-around Mode

In most systems the go-around mode is armed as a standard procedure whilst

on final approach.

GA is armed automatically when flap is selected or on capturing the ILS

glideslope.

When required, the go-around button on the throttle lever is pressed,

commanding the A/T to set go-around thrust, until a satisfactory rate of climb,

about 2,000 fpm, is achieved; the autothrottle will then reduce power, to maintain

2,000 fpm at current airspeed.

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Auto Throttle