The central maintenance system controls the maintenance functions of other avionics systems. It uses a central controller to identify a defective system or line-replaceable unit (LRU). The central controller supplies the computer interface between the crew and the central maintenance system. The central controller uses the performance data to identify a defective LRU.

CAIMS is a distributed interactive aircraft maintenance system installed on the aircraft. The distributive nature of the system means that each Member System has its own set of CAIMS accessible maintenance functions. A Member System refers to any system installed on the aircraft that complies with the CAIMS interface requirements and implements the features of CAIMS. It connects to other avionics systems through the avionics-standard-communications bus (ASCB) or ARINC-429 busses.

The primary function of CAIMS is to: 

• Monitor aircraft performance data
• Record system fault data
• Identify a defective LRU
• Control built-in test (BIT) functions
• Supply maintenance procedures

CAIMS automatically and continuously collects and records performance data from other avionics systems. The maintenance crew and the flight crew use this data for troubleshooting. The maintenance crew uses CAIMS to make necessary repairs and adjustments.

The Portable Maintenance Access Terminal (PMAT) provides a single point access to each CAIMS member. The PMAT not only provides access to each member system, it combines all systems into a single maintenance system with a common display. This reduces the amount of Ground Support Equipment required to maintain the aircraft.

The PMAT contains: 

• The CAIMS operation software. The central maintenance system uses this software to control and show the CAIMS functions
  
  
• A data base of diagnostic software used to do LRU and system tests. The system uses the test results to calculate the possible causes of the malfunction
  
  
• A data base of technical publications which shows the available maintenance procedures (e.g., fault confirmation/isolation, removal/installation, adjustment/test). It also identifies the parts necessary to complete the repairs

CAIMS provides modes to view active faults, fault histories, download fault data, run LRU tests, and display real-time data while the aircraft is on the ground. CAIMS can also be used in flight to monitor active faults and print active fault reports.

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