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MAINTENANCE MANUAL

 (2) The FMCs receive and report fault data from the following LRUs.
 (a)  
Captains and first officers clock

 (b)  
EFIS control panel L,R

 (c)  
EICAS computer L,R

 (d)  
ILS receiver L,R

 (e)  
VOR receiver L,R

 (f)  
DME L,R

 (g)  
ADC L,R

 (h)  
IRU L,C,R

 (i)  
Fuel Quantity Processor

 (j)  
TMC

 E. Yaw Damper System (Fig. 5)
 (1)  
The yaw damper system consists of two yaw damper modules (YDM), a control panel, and a test switch.

 (2)  
The YDMs monitor the following LRUs.

 (a)  
YDM Servo L,R

 (b)  
Elect/Hydraulic Pump and Hydraulic System Pressure

 (c)  
IRU L,C,R

 (d)  
ADC L,R

 (e)  
Air/Ground System 1, 2

 3. Operation
_________
 A. Flight Faults
 (1)  
At takeoff the FCCs, FMCs, and TMC will purge previously recorded fault data from memory. Throughout the flight each computer will monitor interfaces, interfacing LRUs, and its own circuitry for faulty operation. Any detected faults will be stored in memory for later use.

 (a)  
Faults detected in-flight can be stored in non-volatile memory and stored in volatile memory. Faults permanently stored in non-volatile memory are for shop use and can only be cleared in the shop. Faults temporarily stored in volatile memory are reported to the MCDP and cleared from memory. Data stored in the two types of memory generally will not be identical.

 (b)  
Faults reported to the MCDP are those that have a flight deck effect.

 (2)  
Transfer of fault data from the FCCs, FMCs, and TMC takes place at touchdown.

 (a)  
At touchdown, when the air/ground system transitions from air to ground and ground speed drops below 40 knots, the MCDP will automatically power up and undergo self test.

 (b)  
Upon successful completion of power up and self test the MCDP will interrogate the FCCs, FMCs, and TMC for stored fault data, initiating automatic transfer.

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757
MAINTENANCE MANUAL

Yaw Damper Bite Interface and Sensors
Figure 5

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MAINTENANCE MANUAL

 (3)  
Data transferred to the MCDP at touchdown is stored in non-volatile memory. Two classifications of flight faults are last faults and previous faults.

 (a)  
Last flight faults are those occuring during the last flight leg and represent faults that currently exist.

 (b)  
Previous flight faults occured prior to the last flight leg. The MCDP can store up to 99 past flights if no more than 10 past flights have reported faults. This data is for historical use, checking reoccurring faults, or holding data for later use.

 (c)  
Flight fault data stored in the MCDP can only be erased in the shop.

 (4)  
Fault messages can be displayed on the MCDP or EICAS if a remote panel is used. The message is displayed in two lines.

 (a)  
Top line of the flight faults messages displays the flight deck effect and historical flight tag. The historical flight tag identifies the flight leg in which the fault occurred. 00 is present fault and 01 thru 99 occurred 1 to 99 flights ago.

 (b)  
Bottom line of the flight faults messages displays the faulty LRU.

 (5)  
　
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