LEFT STCMA
L STAB
CONTROL NOSE UP CONTROLTRIM NOSE
ARMSOLENOID28V DCUP
FWD >4.0`
CONTROL ARM NOSE UP ARMSOLENOID
L BUS
ABOVE CAPT CONT
ARM
EB
UNITS 14.5NOSE DOWN ARM
NOSE WHL TRIM SW'S SOLENOID
DN CONTROL
R STAB
M
F
AFT >2.7`
TRIM NOSE DOWN CONT
M
ARM
28V DCBELOW 3.25
SOLENOIDR BUS UNITS
E
CONTROL CAPT CONT COLP CLOSE CUTOUT SW'S
T
FLAPS BELOW .2
P11 F/O CONT WHLUNIT
RETRACTEDTRIM SW'S Q OPEN
U
NO. 1 AIR/GNDL TRIM LIM SELRLY (E3-1)
FWD LIMIT SWITCHESPOSITIONL BRAKE RELEASE
NO. 2 AIR/GND
(P36)
V
L STAB POSN INDXDUCERNO. 1 AIR/GND
AFT
(P37)  C
(P10)
(P36)

L RVDTDN UP
NO. 2 AIR/GND
N
BRAKE RELEASE L STLM
L
(P37)
CAPT CONT COL
AUTO TRIM VALID ASYMMETRIC SW'S
MOTOR (E5-1)
FSEU 1 BRAKE
FLAP RET
H

C RVDTSTABILIZER
L SPM
1
L FCCBALLSCREW
STAB POSN
2
FSEU 2
(E2-1)
GREENBAND SW'SACTUATORL ADC
H  (E5-3) ASSEMBLY
1
FLAP RET POSITION
C FCC(E2-1)L SAM (E3-1) C SPM
I
STAB POSN XDUCER
(E2-3)
I
2
BRAKE MOTOR FSEU 3/FSAM
FLAP RET C STLM
R ADC
1
(E5-2)
R FCC(E2-2)
(E2-2)

J
R SPM R RVDT
AFT
DN UP
J
POSITION
STAB POSN XDUCER
FWD
AUTO TRIM VALID LIMIT
CONTROL
K
SWITCHES
R STAB POSN IND
L STAB
F/O ASYMMETRY
TRIM NOSESAME AS
(P10)
SW'S
POSN IND  A UPLEFT 28V DC
O
L BUS

N K
NOSE UPARM SOLENOIDSP11R CLOSE
SAME AS
F
R STABOPEN
CAPT'S
S
TRIM B
POSN IND ARM
NOSE DOWN
R BUS

28V DC
SOLENOIDS L STAB
O
NOSE
STAB TRIM
F/O CUTOUT SW'S R TRIM LIM SELR STLM
TRIM

DN RLY (E4-1)
CUTOUT
P
28V DCCONTROL
NORMC
Q
L BUS R STAB
BRAKE RELEASETRIM
CUTOUT
V
28V DC
R
STAB TRIM LIGHT
R STCM
R BUS NORM
S
STAB TRIM
MACH/SPD TRIM LIGHT
UNSCHD STAB TRIM
P11 (P10)
U
MACH/SPD TRIM2
UNSCHED STAB TRIM LIGHT
1
AUTOMATIC STABILIZER TRIM SYSTEM ONLYCONFIG
L AND R EICASEICASR SAM (E4-1)
T
2 MACH TRIM SPEED STABILITY SYSTEM ONLY (P5) COMPUTERS DISPLAY
Mach Trim Speed Stability Block Diagram
Figure 2

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 22-24-00
 ALL  ú ú 01 Page 3 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL

 (a) Speed Stability Control Law 1) When the speed trim mode engages, the speed trim control law synchronizes to the stabilizer position. The control law provides incremental stabilizer position changes dependent upon computed airspeed-knots (Vc) when the flaps are extended. The Air Data Computers (ADCs) provide digital Vc inputs. Half-speed trim (0.1 to 0.25 degrees/sec) commands are provided by the selected SAM. The speed stability mode is disengaged when the airplane is on the ground and until 20 seconds into the in-air mode.
 2)  After each trim event the stabilizer position change is equal to or above the speed control law (more negative) for increasing speeds, and equal to or below the control law (more positive) for decreasing speeds. {The threshold of speed change for the initial trim event following deviation from trim speed is nominally 5 knots. This is required to protect the system from unwanted trim activity caused by air stream turbulence. The threshold of speed change for subsequent trim events is approximately 2.5 knots. This requirement is based on the tending of the system to overtrim the schedule stabilizer position changes.
STABILIZER POSITION (DEGREES)
-6.0
-5.0
-4.0
-3.0
-2.0
-1.0
0.0

50  100  150  200  250  300 
COMPUTED AIRSPEED, Vc - KNOTS 
 COMPUTED MACH, MC 
___________________________SPEED STABILITY CONTROL LAW _____________________MACH TRIM CONTROL LAW 

Mach Trim/Speed Control Law Schedule
Figure 3

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