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T/R INDICATING AND FAULT DETECTION -T/R POSITION TRANSDUCER (RVDT)
Training Information Point
When you replace the RVDT, do not turn the gearbox square shaft. The new RVDT is shipped from the supplier with protective caps with the square shaft in the null position. If the gearbox shaft is turned, you have lost the null position and you must re-rig the RVDT to find the null output voltage.
The steps for rigging the RVDT are in the supplier component maintenance manual (CMM) as part of an accuracy test. To rig the RVDT back to the null position requires a bench test setup which would include a power supply capable of providing 6.00 VRMS ± 0.1 % at a frequency of 2949 Hz ± 0.1%, a rotary revolution counter, a switch box for excitation and output signals from channel A and B, and a digital multimeter with 0.1% accuracy. The shaft position is critical because you cannot overshoot or reverse the rotation direction as you position the shaft. The shaft rotation must be smooth to each data point you take in the counter-clockwise and clockwise directions as you try to find the null position.
The RVDT on the 777 PW4000 thrust reverser has different electrical characteristics than the RVDTs on other thrust reverser/engine models (Rolls-Royce and General Electric) because of the EEC. These RVDTs are not interchangeable. The physical characteristics (weight and size) of all the RVDTs are similar.
EFFECTIVITY BEJ ALL 78-36-00
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T/R INDICATING AND FAULT DETECTION -RVDT
EFFECTIVITY BEJ ALL 78-36-00
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D633W101-BEJ May 05/2003
T/R INDICATING AND FAULT DETECTION -INDICATIONS
General
Flight deck indication of the thrust reverser (T/R) position shows on the EICAS display, status display, and EPCS maintenance page 1. Any system failure that reduces the level of safety of the system is shown on both the EICAS display and the status display. There are no alert messages that are shown in flight. Thus, no crew action is necessary for thrust reverser system faults.
For system faults, the CMCS has maintenance messages to aid in fault isolation.
EICAS Display
The thrust reverser position indication is shown above the N1 data on the EICAS display.
When one thrust reverser sleeve extension is 5 percent or more, the amber REV indication is shown on the EICAS display. This tells the flight crew that the thrust reverser is released and in transit.
When both sleeves are 90 percent extended, the amber REV indication changes to a green REV indication. This tells the flight crew that the thrust reverser is fully extended.
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