11.18 - On Board Maintenance Systems Flashcards
Explain the differences between on-board maintenance bite and traditional standalone LRU bite tests?
LRU = Line Replaceable Units
BITE = Built In TEST Equipment
On-board maintenance BITE automatically checks the parameters in a system when starting up (initialization test/power up check) and during operation, the system is continually monitored. If a fault occurs, it will be sent to the CMC (Central Maintenance Computer)
The standalone LRU (Line Replaceable Units) that have BITE indicate the status of the LRU with a light, green shows a normal working condition while red indicates a fault with that particular LRU.
Explain the difference between the two interrogation modes in flight and on ground?
The interrogation mode in flight (Reporting mode) means that the Central Maintenance System permanently records and displays failure messages from each of the aircraft’s systems.
The interrogation mode on ground (Interactive mode) allows testing of the aircraft systems, sensors and actuation of system components such as valves and pumps.
What happens when one Central Maintenance Computer fails?
Aircraft on-board maintenance systems have 2 CMCs for redundancy, one active and one standby. Should the active CMC fail, the standby CMC becomes active automatically. This switching of CMCs can also be done manually.
Explain Class 1, Class 2 and Class 3 faults.
The CMC (Central Maintenance Computer) divides faults into 3 classes depending on severity.
Class 1 faults are the most severe, they constitute a NO GO condition or may limit the conditions of the aircraft flight depending on the MEL. They will generate a visual and aural warning in the cockpit.
Class 2 faults allow the aircraft to operate normally as with these faults, the system will still be working normally but possibly without full redundancy. A notification message will be displayed to the crew. It may be possible to defer a repair of a class 2 fault.
Class 3 faults have no affect on the operation of the aircraft. The crew are not alerted to them, they consist of minor problems with a system and are accessed by maintenance crew within the CMC records.
Explain structure monitoring and what does it allow?
Structure monitoring ( Damage Tolerance monitoring) is the monitoring of Fatigue Critical Structure (FCS) as the aircraft ages. Pressurisation cycles, hard landings, corrosion and even repairs can all stress and alter aircraft structural strength.
It allows cracks and other structural irregularities to propogate before being inspected and tested through a DTI (Damage Tolerance Test), they can then be monitored and repaired before structural integrity is compromised.
