The Rockwell Collins MDS-3100/4100 Maintenance Diagnostic System performs an integral function within Pro Line 4 and Pro Line 21 systems by monitoring avionics and aircraft systems to detect failures, identifying LRUs requiring replacement and logging fault data to permit diagnosis of intermittent faults. Along with the system's ability to provide avionics maintenance diagnostics, the MDS-3100/4100 can also display aircraft systems data, engine maintenance information and extensive airframe/user customized checklists that depend on aircraft configuration. In addition, the MDS-3100/4100 provides test and rigging functions for supporting system LRUs, remote access of maintenance information through a PC or portable maintenance access terminal and support for downlinking of maintenance reports via ACARS. With this level of system flexibility, the effective maintenance of the aircraft is increased along with significant cost of ownership benefits being realized.