ENGINE CONTROL SYSTEM - DESCRIPTION AND OPERATION
1. General
A. The engine control system for each engine is divided into three subsystems: the forward thrust
control system, the reverse thrust control system, and the start control system (Fig. 1).
B. The forward thrust control system consists of a thrust lever assembly for each engine,
connected to each engine fuel control unit by control cables, a push-pull cable, and a rod
linkage. The forward thrust control system regulates the engine fuel flow, and hence forward
thrust.
C. The reverse thrust control system consists of a reverse thrust lever for each engine connected
to each engine fuel control by the same control cables, push-pull cable, and rod linkage used to
control forward thrust. However, the reverse thrust control system causes cable travel in the
opposite direction and actuates the thrust reverser. The system regulates fuel flow to the
engine, and hence reverse thrust. A lockout mechanism prevents simultaneous motion of the
forward and reverse thrust levers.
D. The start control system consists of a start lever assembly for each engine, connected to each
engine fuel control unit by control cables, a push-pull cable, and a rod linkage. The start control
system controls energizing the ignition system and initiating fuel flow to the engine.
E. On GJ ALL EXCEPT B-2509, B-2510, drum and friction brake assemblies are installed in the
throttle control cable runs. The brake assemblies are located between floor beams at the aft
end of the electronic equipment compartment.
On GJ B-2509, B-2510, integrated autothrottle servomechanisms are installed in the throttle
control cable runs. The servomechanisms are located between floor beams at the aft end of the
electronic equipment compartment. In the autothrottle mode, the system is controlled by the
autothrottle computer and the throttle levers are driven through the servomechanisms (Ref
Chapter 22, Auto Flight).
F. A drum and shaft assembly for each engine is mounted on the forward face of the front wing
spar. It extends through the horizontal firewall into the engine nacelle strut and transmits engine
control cable travel to the push-pull cable assemblies. A stop pin in the drum-and-shaft
assembly stops start drum travel when the start lever on the control stand is in the CUTOFF
position.
G. Each engine start lever is connected by cables to the drum-and-shaft assembly. A push-pull
cable assembly connects a crank on the start shaft to a crank on the engine cross shaft. A
linkage rod connects a crank on the right end of the cross shaft to a lever on the fuel control
unit.
H. The thrust lever assembly, drum and friction brake assembly, or autothrottle servomechanism,
and drum-and-shaft assembly are cable connected. A push-pull cable assembly connects a
crank on the drum-and-shaft assembly to a crank on the engine cross shaft. A linkage rod
connects a crank on the right end of the cross shaft to the power control shaft crank on the fuel
control unit.
I. Actuation of the thrust lever assembly regulates fuel flow in the fuel control unit. For reverse
thrust, the lever assembly movement actuates the thrust reverser before increasing fuel flow. It
should be noted that the direction of travel of the thrust control cables and drums is the same
for decreasing forward thrust as it is for increasing reverse thrust. When reverse thrust is
increased, a temperature indicating detent is encountered. The detent serves as a caution to
the captain and first officer that it is possible to exceed allowable engine temperature limits if
the reverse thrust lever is held in a position beyond the detent.
2. Thrust Lever Assembly
A. Two thrust lever assemblies on the control stand control the forward thrust and reverse thrust of
the engines. Each thrust lever assembly consists of a forward thrust lever, a reverse thrust
lever, a reverse thrust detent mechanism, a thrust control link, a pawl and a thrust control drum
(Fig. 2). The forward thrust lever, with the reverse thrust lever attached to it, is concentrically
mounted with the thrust control drum. One end of the control link is riveted to the reverse thrust
lever and the opposite end is attached to the thrust control drum. An autothrottle disconnect
switch and a go-around (or auto-take off and go-around) switch is incorporated in the thrust
lever assembly (Ref Chapter 34, Navigation).
B. As the thrust lever is advanced from the idle position, the control link rotates the thrust control
drum to actuate the fuel control unit to increase thrust. The forward thrust idle position is
against an idle stop on the control stand cover and full forward thrust is obtained before the
lever is all the way forward. The reverse thrust lever, when in the OFF position, is against an
idle stop on the forward thrust lever.
C. A lockout mechanism prevents simultaneous actuation of the forward and reverse thrust levers
to assure positive forward or reverse thrust control. The ability of each lever to move depends
on the position of the other lever. If the forward thrust lever is more than slightly forward of the
idle position, the reverse thrust lever cannot be moved more than a small travel aft from OFF.
However, if the reverse thrust lever is moved more than a small travel from OFF, the forward
thrust lever cannot be moved. The lockout between the levers is a pawl, riveted to the forward
thrust lever (Fig. 2). The pawl is between the thrust lever and the control link. When the forward
thrust lever is in the idle position the pawl is aligned with a lockout hole in the web of the control
stand thrust lever cover. As the reverse thrust lever is moved from the OFF position, the control
link forces the pawl into the hole to lock the forward thrust lever in the idle position. As the
reverse thrust lever is returned to the OFF position the control link pushes the pawl from the
hole to unlock the forward thrust lever. When the forward thrust lever is more than slightly
forward of the idle position, the pawl is not aligned with the lockout hole. The web then opposes
the force of the control link on the pawl so the reverse thrust lever cannot be moved more than
slightly aft of OFF.
D. The thrust lever contains reverse thrust power indicating detents.
3. Engine Start Lever
A. Two engine start levers on the control stand are used to start the engines. Each lever controls
energizing the ignition system and initiating or shutting off fuel flow to the respective engine by
switch actuating cams on the start control drum. The start lever is provided with a spring-loaded
detent catch which may be released by lifting the knob. A detent secures the lever in the
CUTOFF and IDLE positions.
4. Engine Control Cables
A. Engine control cables consist of engine start and thrust cables which connect the drum-andshaft
assemblies at each engine to the respective engine start lever and thrust lever. The
cables are routed from the control stand under the floor, thru the body shell and out the forward
face of the wing front spar to the engine control drum-and-shaft assemblies. The thrust control
cables also pass through the drum and friction brake assembly or autothrottle servomechanism.
5. Integrated Autothrottle Servomechanism (GJ B-2509, B-2510)
A. The integrated autothrottle servomechanism is composed of a torque switch mechanism, an
actuator assembly and a throttle position sensor (Fig. 4).
(1) The torque switch mechanism consists of input and output quadrants with an integral cam
to operate switches, a mechanism to permit pilot override of the servo drive, a means of
generating braking friction to prevent throttle creep in the manual mode, and a support
framing with two removable control cable guards and locating dowel pins.
(2) The actuator assembly consists of a servo motor with reduction gearing to form the prime
mover, an electromagnetic clutch, a tachometer to provide servo motor speed signals, and
electronic circuitry which, when controlled by the autothrottle computer, drives the output
when the input has contacted a stop at the idle position.
(3) The throttle position sensor consists of a potentiometer connected by a shaft to an input
gear which is meshed with the torque switch mechanism idler gear. The throttle position
sensor measures output quadrant travel and provides the position signal to the flight
recorder.
6. Engine Control Drum-and-Shaft Assembly
A. An engine control drum-and-shaft assembly provides a mechanical link between the thrust and
start control cables and the push-pull cable assemblies. The assemblies are located on the
forward face of the wing front spar and extend through the nacelle strut firewall. The assembly
consists of concentric thrust and start control drums and shafts, and a start and thrust crank.
Cable travel is transferred by the drums and shafts to the cranks on the end of the shafts.
7. Engine Control Push-Pull Cables
A. A pair of push-pull cables transfer thrust and start control travel from the thrust and start cranks
on the control drum and shaft assembly to the cranks on the left side of the engine cross-shaft.
The cross-shaft transfers crank travel to the right side of the engine.
8. Cross-Shaft to Fuel Control Linkage
A. The cross-shaft to fuel control linkage consists of a start rod and a thrust rod. These rods make
the final engine control motion transfer, from the right side of the engine cross-shaft to the fuel
control unit
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