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Central Maintenance System

Gulfstream G450 Systems

The crux of the Central Maintenance System (CMS) is the Central Maintenance Computer (CMC) and FlightSafety says "the CMC has no impact on the safety of the aircraft. The CMC is intended for maintenance personnel and gives them single point access to all member systems."

That simply is not true. If the CMC malfunctions, you can find yourself without DUs, charts, or other normal operating systems. It might be intended for maintenance personnel, but pilots need to understand it unless they never fly without a mechanic on board.


What is the CMC?


Figure: CMC Module and Location, (FSI G450 MTM, figure 45-3)

[FSI G450 MTM, Chapter ATA 45, pg. 10]

  • The Central Maintenance Computer (CMC) system is a hardware and software installation that provides the operation, storage, and interfaces for maintenance data.
  • The CMC is needed to load much of the software needed to make the airplane operate.

  • The flight crew may access data generated by the CMC by selecting the CMC synoptic page for view on the Display Units (DUs).
  • Data is also downloadable by connecting a portable Personal Computer (PC) directly to the CMC module in the MAU using Ethernet ports.
  • The CMC has no impact on the safety of the aircraft. The CMC is intended for maintenance personnel and gives them single point access to all member systems.
  • We have had various systems on the airplane malfunction where the required fix was to reload the software. It is true the airplane will fly without it, but you may be without DUs and that is no way to fly this kind of airplane.

  • They can view the fault histories of member systems, transfer files to or from the aircraft, initiate test modes for member systems and display real time fault status.
  • The CMC is used as a tool to diagnose and repair failures within the aircraft member systems.

How is the CMC powered?


Figure: CMC left E-Batt, (FSI G450 MTM, figure 45-4)

[FSI G450 MTM, Chapter ATA 45, pg. 16]

  • The CMC operates using Windows technology. As with any Windows product, there is a two minute power up period before it will be available for use after the aircraft is initially powered up.
  • On shutdown, the same applies. The CMC must have two minutes of power to shutdown its functions. To accomplish this, the CMC will utilize the Left Emergency Battery located in the LEER for power to complete its shutdown cycle after aircraft power is secured (Figure 45-4). The power source is a direct line from the L E-Batt to the CMC SHUTDOWN POWER circuit breaker (LEER H6), to the CMC modules front connector.
  • I've heard there are crews that pull the circuit breakers on the E-Batts with the idea they are saving an internal clock that requires the E-Batt be replaced after so many hours of life. As far as I know, there is no such internal clock. But if you insist on doing this, you need to make sure the CMC has at least two minutes to power down.

  • With this design, it is very important to never have the L E-Batt removed or have its front panel circuit breakers pulled, or have the “CMC SHUTDOWN POWER” circuit breaker pulled during an aircraft power down cycle. If this occurs, it is possible for data corruption to occur or the CMC can become “locked” and unavailable to the operator. These conditions will require the CMC to be repaired by a Honeywell repair facility.

How is the CMC connected to the LAN?


Figure: CMC Data Management Unit (DMU), (FSI G450 MTM, figure 45-7)

[FSI G450 MTM, Chapter ATA 45, pg. 19]

  • The Data Management Unit (DMU) provides the CMC with a LAN connection to a DVD-ROM drive and two PCMCIA data storage cards. The Data Management Unit’s PCMCIA slot 2 (bottom slot) can be used to transfer the fault history database reports and the Aircraft Condition Monitoring Function reports from the CMC memory to a PCMCIA card for viewing on a personal computer.
  • While this was certainly true early on, the connection between the PCMCIA and DVD-ROM have been problematic and new solutions involve going through the System Monitor Test Panel, which has proven to be much better.

    See System Monitor Test Panel, below.

  • There are lights next to the PCMCIA slots on the DMU. When the DMU door is opened, the lights will turn amber indicating that the PCMCIA cards are shutting down. The cards should not be removed until this process is complete and the light turns green. The PCMCIA cards will not power back up until the DMU door is closed and secure.
  • The Data Management Unit (DMU) is located in the cockpit on the pilot’s side console. It is mounted on the wall of the panel and not on top as in other typical aircraft installations. Care should be taken when opening the DMU because it could be damaged if the pilot’s seat is moved backward during a DMU loading procedure.

How do you "flag" and event for the CMC?


Figure: CMC FDR/CMC event switch, (FSI G450 MTM, figure 45-8)

[FSI G450 MTM, Chapter ATA 45, pg. 20]

  • The FDR / CMC EVENT switch is located on the cockpit overhead panel. When selected, the CMC will create an ACMF report based on predefined parameters. The triggers and report parameters are defined by Gulfstream Engineering.
  • It isn't quite so easy. If you want to tell the CMC to make a record of something, you first need to let it know what to look for. That will require a software load first. Contact Gulfstream Technical Operations for more about this.

  • The ACMF report will consist of a 200 second “time-series” recording; 100 seconds before the event and 100 seconds after the event.
  • When the recording is taking place, a blue advisory Event Record CAS message will be displayed.

Where does the data reside?


Figure: CMC Database Module, (FSI G450 MTM, figure 45-10)

[FSI G450 MTM, Chapter ATA 45, pg. 10]

  • Database Module in MAU 3 Slot 1 is utilized by the CMC function. The database module provides the CMC with 120 MB of storage, accessible via File Transfer Protocol (FTP) services. The CMC uses this storage space primarily for redundancy. It stores a backup of the fault history database in this area.
  • The backup occurs in two phases, ground to air, and air to ground transitions. If the CMC FHDB is lost or corrupt, it will download the most recent copy from the database module.
  • Depending on aircraft configuration aircraft are equipped with zero, one, or two database modules. Aircraft which have no database modules will use the TNIC card as backup storage which serves the same functions mentioned above.

How do you (the pilot or mechanic) get to the data?


Figure: CMC System Monitor Test Panel, (FSI G450 MTM, figure 45-11)

[FSI G450 MTM, Chapter ATA 45, pg. 10]

  • Ground Maintenance Test Switch
    • The CMC has the ability to provide the user an interface to perform various actions on the member systems (i.e. IBIT). Before any of these actions can be performed on the associated member system, the ground maintenance test switch must be initiated to enable these modes in the CMC.
    • The switch sends a ground discrete to the SGIO 1 MAU 1 Slot 3 and SGIO 4 MAU 2 Slot 12. If both of these discretes are not received, the associated action that is being requested will not be performed.
    • To validate these discretes, the CMC will display the status of the SGIO input on the bottom of the Systems Diagnostic main display page (ACTIVE or NOT ACTIVE).
    • The CMC will only display some of its functions with this switch activated.


Figure: CMC Remote Terminal, (FSI G450 MTM, figure 45-12)

[FSI G450 MTM, Chapter ATA 45, pg. 10]

  • LAN Bus Port
    • Two Ethernet ports are located on the System Monitor Test Panel which is mounted on the forward side of the REER above the Observer Seat (Figure 45-11). These two ports are used to connect the Remote Terminal (laptop) to the Central Maintenance Computer via the Local Area Network (LAN).
    • The Local Area Network is used to transmit Electronic Terminal Charts to the Advance Graphic Module, and is used for all aircraft software data loading. It is very important to maintain the integrity of the LAN throughout the Modular Avionics Units, Data Management Unit, Cockpit Printer, Central Maintenance Computer, and Modular Radio Cabinets.
    • You normally interface with the CMC by connected a coax cable to one of the top connectors on the top of this panel. (It doesn't matter which.) There is a definite protocol to all of this. If you ever have to update the databases, this is where you start.

      For more about this: PlaneView Database Update.


* FSI G450 MTM, FlightSafety International Gulfstream G450 Maintenance Training Manual, August 2008

* FSI G450 PTH, FlightSafety International Gulfstream G450 Pilot Training Handbook, Revision 6, July 2010

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Revision: 20161219