In the course of time numerous complaints have been written about the P5 panel REVERSER light. Illumination of this light has been reported in various phases of operation and in most cases it had an intermittent behaviour. This article discusses the EAU bite procedure in brief but is primarily intended to emphasize that proper troubleshooting and reporting is essential to isolate faults that causes the light to illuminate.

There are several factors that may be responsible for the REVERSER light illumination, which is generated by the Engine Accessory Unit (EAU). The EAU monitors the following:
– The sleeve stow and lock proximity sensors.
– The Hydraulic Isolation Valve (HIV) and Directional Control Valve (DCV) proximity
sensors.
– The voltage input to each sync lock.
If one or more of these inputs are not in their commanded state, this is indicated by fault lights on the EAU. Normally the EAU keeps faults in the memory for the last five stow and deploy cycles. However, this data will be cleared instantaneously (if not active) by pushing the applicable EAU FAULT RESET button.
Note: During normal operation, the REVERSER light only comes on for 10 seconds when a T/R travels to stow.
EAU BITE procedure
To investigate a REVERSER light complaint, follow the EAU BITE Procedure as described in FIM TASK 78-31-00-810-801-F00. When pressing the applicable FAULTS button on the EAU, one or more maintenance messages may be displayed by means of red lights. The fault isolation tasks for these messages are mentioned in ‘BITE Table 78-31’ of afore mentioned FIM chapter. If more than one maintenance message is shown, be aware to select the fault isolation task for that combination of maintenance messages
for trouble shooting. A detailed description of the corrective maintenance action should be recorded in the ATL.

EAU reset
After a stow fault is corrected, the relevant P5 panel REVERSER light in the flight compartment will go out.
However, the EAU T/R STOW FAULTS light will stay on until the EAU is reset.
After a deploy fault is corrected, the P5 panel REVERSER fault light and the EAU T/R DEPLOY FAULTS light will stay on until the EAU is reset. The thrust reverser must be in the deploy position to reset the deploy faults in the EAU.

Intermittent fault
Numerous occasions have been reported of intermittent REVERSER light illumination. In most cases the complaint cannot be reproduced during trouble shooting. However, one or more maintenance messages may be stored in the EAU.
In this situation it is very important first to look for possible EAU maintenance messages before testing and resetting of the system. Recording this information in the ATL  is crucial for efficient troubleshooting in case the complaint reoccurs. It will also help to prevent unnecessary repetitive maintenance actions.

Thanks to CE for this input.

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