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1. The engine thrust control module (TCM) supplies control for the forward and reverse thrust of the engines.
2. The TCM is also used for:
- Fuel control
- Autothrottle disconnect
- Takeoff/go-around (TO/GA) commands
- Reverse thrust selection and control.
3. The TCM has these external parts:
- Forward thrust levers (2)
- Reverse thrust levers (2)
- TO/GA switches (2)
- Autothrottle disengage switches (2).
4. The fuel control switches send signals to open or close fuel valves to operate or shutdown the engines.
- They send signals to the remote data concentrators (RDC) and the spar valve start switch relays.
- The spar valve start switch relays use these signals to control the spar valve and the high pressure shut off valve (HPSOV) in the fuel metering unit (FMU).
- The RDCs send the signals to the common data network (CDN) and then to the electronic engine control (EEC) to operate the FMU fuel valves (FMV and HPSOV).
5. The fuel control switches have 2 positions:
- RUN
- CUTOFF.
6. You must pull the switch out of a detent to select a position.
7. The switch handles have red light emitting diodes (LED) that come on when there is an engine fire.
8. Forward and reverse thrust lever position is sensed by 2 thrust lever angle (TLA) resolvers for each engine partitioned within the TCM.
- Each resolver is hardwire connected to a channel (A or B) of the EEC.
- Thrust resolver angle (TRA) is used by the EEC to calculate fuel demand.
9. A T/R lockout solenoid makes sure the T/R levers are locked to prevent accidental deployment of the T/Rs.
System Description Section (SDS)
The engine thrust control module (TCM) supplies control for the forward and reverse thrust of the engines.
The TCM is also used for:
- Fuel control
- Autothrottle disconnect
- Takeoff/go-around (TO/GA) commands.
Physical Description
The TCM has a housing with an internal partition that isolates the left and right sections. Each section has these parts:
- Forward thrust lever
- Reverse thrust lever
- Autothrottle disconnect switch
- TO/GA switch
- Thrust reverser (T/R) lock mechanism
- Resolver mechanism
- Servo motor
- Interface connector.
The 2 printed-circuit boards and ARINC 429 interface are in isolated aluminum enclosures that attach to the TCM and connect with a cable harness.
One fuel control switch is in each section of the housing. Each switch has a connector to permit replacement on the without removal of the TCM.
Redundant components are included in the linkage between each thrust lever, reverse thrust lever, and the resolvers. This gives a safety feature for single
point or dormant failures in the system.
Switches
The takeoff/go-around (TO/GA) switches are 3 single-pole, single-throw snap action switches. The switches are on the forward part of each forward thrust lever knob and operate with 28v dc.
The autothrottle (A/T) disconnect switches are a momentary push-button, single-pole single-throw, double-break unit. The switches are on the outboard side of each throttle knob and operate with 28v dc.
The fuel control switches are on a plate on the front of the TCM below the thrust levers. The fuel control switches have RUN and CUTOFF positions.
Each switch has a detent to prevent accidental movement. The switch handles have internal red light emitting diodes (LED) that come on when a related engine fire condition is sensed. Each switch is a toggle type with a cap. The cap can be removed for replacement of the internal LED lamp.
Reverse Thrust Lever
You can move the reverse thrust levers at the idle power position only. The reverse thrust lever is blocked when the forward thrust lever is forward of idle a minimum of 3 degrees. The forward thrust lever is blocked when a reverse thrust lever is moved more than 8.5 degrees.
Each lever travel is 87 degrees from the stowed to maximum movement position. A bidirectional detent gives pilot indication. The detent force is 6 lbs (2.7 kg).
An additional friction adjust mechanism sets the reverse thrust lever operation feel independently from the forward thrust lever friction mechanism as a safety feature. Track lock and directional control valve (DCV) is at 21 degrees of reverse thrust lever angle. Lever travel is interrupted at 45 degrees with the solenoid operated interlock mechanism in the TCM. The interlock releases when the solenoid is energized by a signal when the T/R sleeves are deployed. The lock release lets the reverse thrust lever go to the maximum reverse thrust position.
The T/R switches use 28v dc. The interlock mechanism and solenoid operates with a maximum 5 lbs (2.4 kg) force applied to the reverse thrust levers. The solenoid has a circuit that regulates the current flow to maximize solenoid pull force. This gives maximum current at initial stroke and minimum current after full stroke.
Position Resolvers
Each lever operates 2 isolated resolvers through a dual gear/linkage drive.
This gives redundancy and safety for single point failures.
Autothrottle
The thrust management system controls the autothrottle servo drive. The servo drive system gives 2-way communication with the autothrottles on the ARINC 429 interface. Built-in test (BIT) is included in the servo drive system.
Servo motors drive the levers directly through a worm/gear system with a high gear ratio. This gives a lever speed of 0.5 to 15 degrees per second. The servomotors drive the levers through a friction clutch that permits manual override by the crew while in thrust management control. The mechanism has 2 motor control units (MCU) and 1 signal conversion unit (SCU). The units are in an aluminum enclosure.
Electronics Box
The printed circuit (PC) boards are in an aluminum housing on the TCM housing. It interfaces with the module through 5 connectors. The electronics box is environmentally sealed for protection.
Operation - Engine Thrust Control Module
1. Each thrust lever mechanically connects to 2 thrust lever angle (TLA) resolvers, which send thrust lever resolver angle (TRA) data to the EEC for
thrust control.
2. The thrust control system can continue normal operation with a failure of one resolver.
3. The EEC reads each winding and validates that the voltage is in range.
- If the signals pass these electrical checks, but the 2 TRA signals disagree, the EEC selects the higher value to maintain maximum thrust setting capability and selects the value closest to idle for thrust control malfunction accommodation (TCMA) to protect against uncontrolled high thrust (UHT) on the ground.
4. If both TRA signals are out of range, the last valid TRA value is used.
5. If both resolvers fail electrically, the EEC holds the last valid value for 2 seconds, then sets the engine thrust to idle.
- Default to idle thrust is acceptable because it only affects one engine.
6. The thrust management function (TMF) of the common core system (CCS) supplies thrust command signals to the autothrottle servo motors to operate the thrust levers.
7. The reverse thrust levers are on the thrust levers.
8. The TO/GA switches send signals to the autoflight and the thrust management function (TMF) to start the TO/GA mode.
9. The autothrottle disconnect switches send signals to the TMF to disengage the autothrottle.
10. The fuel control module (FCM) is on the aft end of the thrust control module
- It sends signals to open or close fuel valves to operate or shutdown the engines
11. The FCM sends signals to the:
- Spar valve start switch relays
- Common data network (CDN).
12. The spar valve start switch relays use these signals to control the spar valve and the high pressure shutoff valve (HPSOV) in the FMU.
13. Remote data concentrators (RDC) send fuel control module signals to the CDN.
- The signals go to the engine electronic controller (EEC) to operate the fuel metering unit (FMU), fuel metering valves (FMV), and high pressure shutoff valve (HPSOV).
14. TRA shows on the engine propulsion control system (ECPS) page.
15. The T/R lockout solenoid usually is not energized.
- It operates with the lockout arm to block the reverse thrust levers when a thrust lever is forward of the idle position (this is an interlock mechanism).
- This interlock also blocks the thrust levers when they are at idle and a reverse thrust lever moves.
- The T/R lockout solenoid and lockout arm blocks the reverse thrust levers when the thrust lever is forward of idle.
16. The T/R lockout solenoid also energizes by a command from the EEC when conditions are correct to operate the T/Rs.
- This lets full movement of the reverse thrust levers.
- The T/R lockout solenoid and lockout arm blocks the reverse thrust levers when the thrust lever is forward of idle.
17. When the fuel control switch is set to the RUN position:
- Airplane electrical system power is removed from the FMU shut-off coil to enable the engine fuel shutoff valve to open by the EEC command when sufficient fuel pressure is provided by the engine rotation to open the valve
- Airplane electrical system power is supplied to the open winding of the airplane spar valve motor
- Airplane electrical system power is supplied to the engine ignition system which then can be turned on or off by the EEC
- Airplane electrical system power is supplied to the EEC until sufficient power is provided by the permanent magnetic alternator (PMA)
- Airplane electrical system power is supplied to the engine monitoring unit (EMU).
System Description Section (SDS)
General
The thrust lever and autothrottle assembly supply thrust commands to the electronic engine control (EEC). You use the thrust levers to make manual inputs. The autothrottle servo motor (ASM) makes automatic inputs.
Thrust Lever
When you move the forward thrust lever, the movement goes down to the thrust lever crank. The forward thrust lever and crank turn on the same shaft.
The crank connects to the ASM. The ASM turns the rotor of the TLA resolver.
The resolver sends a thrust resolver angle (TRA) signal to the EEC.
When the forward thrust lever is not at idle, the lever latch holds the reverse thrust lever down. When the forward thrust lever is at idle, you can lift the reverse thrust lever. When the reverse thrust lever is up, the latch holds the forward thrust lever at idle.
The ASM turns a shaft in the thrust lever assembly through a gearbox. The ASM brake turns the rotor of the TLA resolver and at the same time moves the thrust lever.
Fuel Control Switch
Each fuel control switch controls 2 relays in the power distribution panels. The relays control many functions.
These are the relays:
- Engine fuel control relay 1
- Engine fuel control relay 2.
Engine fuel control relay 1 controls the fuel metering unit shutoff valve.
Engine fuel control relay 2 controls these functions:
- Spar valve control
- Fuel control switch position to the bus power control unit (BPCU)
- EEC channel reset signal
- Fire handle lock solenoid.
