(2) Fault isolation procedures (P. Block 201)
(a) Possible Causes This lists all the suspect items in the fault isolation procedure to allow assembly of all items required to fix the fault. It is not provided for "shotgun" trouble shooting.
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Example of APU Fault Symptom Page
Figure 010
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(b) Fault confirmation
1 Permanent fault
_ The fault is confirmed on ground by performing the test required in the fault confirmation paragraph. Consequently, the procedure must be applied to troubleshoot the A/C.
2 Intermittent fault
_ (INTM) is added to the message when an intermittent operation of the system is detected. Example of message :
NO BSCU DATA (INTM)
The fault is not confirmed on ground by performing the test required in the fault confirmation paragraph. Faults are sometimes generated by electrical transients or similar events without the aircraft system being faulty. If the confirmation test result is "TEST OK" or equivalent, no further action is required (unless specified in the fault isolation procedure). The aircraft may be dispatched. It is recalled that the TSM has been designed to isolate/troubleshoot hard faults. However depending on the airlines organization, the following can be applied "to trap" intermittent faults:
-
if test OK (fault not confirmed) dispatch the aircraft, . then perform a monitoring of the reported symptom on the following flights by checking:
*
the previous leg reports
*
the PFR/Previous PFRs (if available)
*
the log book of the previous flights.
. after 3 occurrences of the same phenomenon (even though
the test is still OK), the other steps of the TSM procedure
shall be followed and the LRU involved be removed.
In this case, as for all LRUs removed from the aircraft,
AIRBUS recommend to provide shop people or suppliers with
data related to the removal: PFR, test result, trouble
shooting data (if available).
-
if test NOT OK (fault confirmed), apply the trouble shooting procedure.
(c) Fault isolation procedure
1 Do not replace (swap) LRUs as a trouble shooting step unless
_ the TSM tells you to do so. After carrying out the fault isolation in accordance with the TSM, to prevent a NO GO situation in the dispatch of the aircraft when no spare is available, swapping of LRUs is permissible in accordance with operator policy.
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CES CAUTION : IF YOU SWAP LRUs :
-MAKE ONE SWAP AT A TIME
-DO NOT SUPPLY THE SUSPECT LRU WITH ELECTRICAL POWER WHEN INSTALLED IN ITS NEW POSITION
-FREQUENT DISCONNECTIONS AND CONNECTIONS CAN INCREASE THE RISK OF DAMAGE TO PLUGS AND RECEPTACLES.
CAUTION : WHEN DOING FAULT ISOLATION ON ETOPS IMPORTANT SYSTEMS, IN
ACCORDANCE WITH THE TSM, IT MAY REQUIRE THE SWAPPING OF
LRUs. THE OPERATOR'S APPROVED MAINTENANCE PROCEDURES MUST
BE FOLLOWED TO KEEP THE ETOPS STATUS OF THE AIRCRAFT.
2_ The TSM does not give the action to be taken if a suspect unit
removed from the aircraft during trouble shooting is found to
be serviceable rather than failed. This is due to differing
replacement policies of airlines on such units (reinstall, or
send to the workshop). If such a situation occurs airline
internal replacement policy shall be applied.
3_ Continuity and isolation checks on LRUs and system wiring made
on the equipment rack ARINC 600 connectors, should only be
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