Here, we are going to brief the sequence of thrust reverser deployment on engine CFM 56-5C installed on the A340-200/300.
Note: The schematic photo is taken from AIRBUS CBT CD / Its here for studying purposes only. It is not allowed to copy it for trading purposes without prior notice from AIRBUS.
The ECU controls the deployment of the thrust level as follow:
1) Taking direct signal from the TLA -Thrust Lever Angle- while aircraft on ground and engines are running. Or taking a signal from EIVMU through the inhibitation logic when the reverser requisition confirmed by the TCU – Throttle control unit-.
The HCU has a Deploy Solenoid Valve and Isolation Solenoid Valve. Also it has Pressure switch and inhibit switch controlled by ECU for reverser control and monitoring.
2) The hydraulic is supplied to the HCU through the Hydraulic Shut Off valve which opens according to the TLA signal computed in the FCPC – Flight Control Primary Controller-.
3) The ECU will energize or de-energize deployment or stowing solenoids to open or close valves for hydraulic to pass through the HCU – Hydraulic Control Unit- which is responsible for the sequence unlocking, deploying, stowing and then locking the reverser doors.
4) When reverser deployment required both solenoids energized, the hydraulic is supplied to the locking mechanism to unlatch the doors then hydraulic supplied to the stow side, the door and actuator will be unlocked the stow switches will send this indication of unlatched reverser on ECAM (REV In AMBER) then the hydraulic will be supplied to the extend side of the pivoting door actuator. When the door is fully open the deploy switches will close and the deploy signal is sent to ECU and indication appears on ECAM (REV In GREEN). The ECU will de-energize the isolation solenoid.
5) When the TLA set back to normal (STOW) the ECU will de-energizes the deploy solenoid and energizes the Isolation solenoid. The hydraulic is then supplied to the retract side of the actuator piston. The deploy switch will open and unstowed will be sent again through ECU. The hydraulic shut off valve will close.
The HCU -Hydraulic Control Unit- consists of:
1) Isolation Control Valve and its solenoid responsible to supply hydraulic to the HCU. Its spring loaded closed, its two positions valve.
2) Pressure switch signals the HCU of hydraulic pressure availability.
3) Directional control valve and its solenoid supplies the actuator.
4) Flow control valve controls the stowing speed of the doors.
5) Deploy solenoid valve supplies hydraulic to the latches.
The hydraulic supplied, the isolation solenoid is energized the hydraulic will enter the HCU, and then the hydraulic pass through the energized deploy valve to release the latches of the four doors actuators one by one. Then the return hydraulic will return to the HCU to pass through the directional control valve which allows fluid flow to the actuators. Both sides of the piston in the actuator have now hydraulic but due to the differential of the area on the piston sides, the actuator will move in the deploy position. When at least one door start to deploy actuator more than .7% of its travel the stow switch will signal the ECU. This will give REV indication in amber On the E/WD. At 94 % of the travel, the door deployment start to decrease in motion and the deploy switch will be activated. REV in green will be indicated when all doors are deployed. Then the ECU will de-energize all the solenoids and the blocker doors remain open by the aerodynamic forces of the FAN AIR FLOW.
When set to stow, the ECU will energizes the isolation valve while the deploy solenoid isn’t energized. The hydraulic flow in the stow direction on the actuator and the flow control valve will control the stow speed. At 94% of the travel the REV on indication returns amber until it disappears at .7% of the travel.
There are four modes for the thrust reverser. They are: 1) Pre-deployment. 2) Deployment. 3) Stowing 4) Locking.
For maintenance purposes, the Thrust Reverser can be tested on ground through the CMC and be deployed without engines run. The CMC will simulate engine N2 conditions to allow the deployment during test.
The thrust reverser operation logic (AND GATE LOGIC) are: TLA position, Aircraft on Ground, and N2 (Engines are running).
B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer
