Honeywell Mark III manual LRU Interfaces, Flight Management Computer FMC, Performance Computer PZ

2.2.3 LRU Interfaces

In general, the Mark III CMU can support any LRU that uses the ARINC 429 File Data Transfer Protocol or Williamsburg Protocol to communicate as an end system, as defined in ARINC 619 (ACARS file transfer protocols for other devices). ARINC 758 identifies a number of specific LRUs and the Mark III CMU supports interfaces to these LRUs:

Flight Management Computer (FMC)

The Mark III CMU can be configured to interface via low speed ARINC 429 with up to three ARINC 702 compliant FMCs operating as end systems. The Mark III CMU can alternatively be configured to interface with up to three ARINC 702A FMCs over high speed ARINC 429. The Mark III CMU can also accept ARINC 429 broadcast data from the FMCs. This broadcast data provides the CMU with data that is captured in the FIDB and available for use by the HGI and AMI.

Performance Computer (PZ)

In some aircraft installations, there is a separate performance computer (PZ) in addition to an FMC. The performance computer communicates with a CDU through the CMU (See Figure 5) via RS-422. The Mark III CMU can support a single interface to a performance computer with a software upgrade.

Performance Computer

NZ-2000

RS-422		RS-422
	Mark III		CDU
	CMU

Figure 5 CMU/PZ Pass Through Interface

Maintenance Computer

The maintenance computer name varies depending upon the Original Equipment Manufacturer (OEM) but is usually referred to as the Central Maintenance Computer (CMC), Centralized Fault Display System (CFDS), or Central Fault Display Interface Unit (CFDIU). The Mark III CMU can be configured to interface with one maintenance computer over low speed ARINC 429. This interface supports both end system communications as well as the maintenance computer protocol.

The maintenance computer protocol varies based upon airframe. The Boeing 747 uses broadcast fault bits while most other air transport aircraft (e.g., MD-10, MD-11, B-717, A-320, A-330, A-340) use an interactive data block transfer utilizing MCDU screens. Other aircraft types do not currently support maintenance computers (e.g., MD-80, MD-90, B-737, B-757, B767, regional and business jets). The baseline Mark III CMU supports the broadcast fault bits. Interactive data block transfer protocol will be available as a planned upgrade.

Aircraft Condition Monitoring System (ACMS)

The Mark III CMU can be configured to interface with a single Aircraft Condition Monitoring System (ACMS) or Digital Fault Data Acquisition Unit (DFDAU) via low speed ARINC 429. This interface supports end system communications using the standard ARINC 619 protocol in addition to providing the CMU access to

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