ONBOARD MAINTENANCE SYSTEM
ATA 45
Prepared By- Sahil Sodhi
B2 Batch III
 Central Maintenance System (CMS)
 CMC
 Fault Classification
 BITE
 MCDU
 ACARS
 Data Loading and Configuration System (DLCS)
 Printing
 Structure monitoring
 The OMS (onboard maintenance system) is composed of above
mentioned systems.
• CMS function is to initiate airplane system tests, record and store test results,
monitor airplane systems.
• CMS operates in two modes :
i) Normal Mode
ii) Interactive Mode
 Interactive mode is always operated on the ground, and always require operator
action.
 All the aircraft systems that are included with an internal BITE Function are
monitored by CMS.
 A typical CMS consists of single or dual central maintenance computers connected
to a printer, data loader, a data reporting/transmission system and multifunction
control display units (MCDU)
 This is the processing unit of CMS.
 The CMC can be a LRU installed in its own mounting rack in an avionics
compartment as found in Airbus or Boeing.
 If not a LRU, It will be removable printed circuit board (PCB) card unit installed in a
card rack such as the IAPS (Integrated Avionics Processing System) in the Rockwell
Collins Proline system.
 CMC’s input will be BITE results which is initiated by CMS.
 Operating software and fault history are stored in the non-volatile memory.
Approximately 500 faults can be stored in the NVM.
 In modern airplane systems ARINC 429 is the most common data bus used to
interconnect airplane systems to the CMC
• Classified in order of priority:
 Warnings are of highest priority and are usually displayed as a RED visual
indication accompanied by a continuous repetitive chime (CRC).
 Cautions are usually displayed as an AMBER visual display, accompanied by a
single chime.
 Advisories, displayed as a
visual indication.
• CMC record these faults as LEVELS. LEVEL A IS WARNING, LEVEL B is CAUTION &
LEVEL C is
• As per AIRBUS there are classes of faults in which warning and caution are of Class
1, all the
are of Class 2 and Class 3 faults are recorded by CMS and is for
maintenance personnel.
 BITE circuitry tests numerous individual parameters to determine whether the
system is functioning properly.
 The individual system BITE circuits are connected to the CMC by a digital data bus.
ARINC 429/629 buses are used for this purpose in many aircraft.
 Categories of BITE test includes: i) Power-on self test (POST)/Initial
ii) Continuous test/Cyclic
iii) Maintenance test/Interruptive
 CMCs are accessed by this unit in the flight deck/cockpit.
 The MCDUs enable the user to navigate the on board maintenance system by
selecting from various onscreen menus.
 Data from the CMS can be relayed to ground stations via an on-board data
management system such as an aircraft communications and reporting system
(ACARS) or an air traffic information management system (ATIMS).
 The ACARS data is transmitted to the ground using VHF communications radio, HF
radio or satellite communications (SATCOM).
 Requires a CMU (Central management unit) to gather data concerning aircraft
position, attitude, speed, fuel status, etc, as well as data from the CMS.
 When ground station request the data through a signal which triggers the ACARS
data transmission then the mode is known as “POLLED MODE”.
 When the flight crew sends the data manually or automatically through ACARS data
transmission the mode is known as “DEMAND MODE”, and in this mode it
automatically sends any data that is going to affect the flight safety of airplane.
 DLCS has mainly 4 functions- i) Data Loading
ii) Configuration Management
iii) Repository Management
iv) Software pin programming
 An aircraft's data loading system provides a means to upload data to, and download
data from various airplane systems, including the CMS.
 multipurpose disk drive unit (MDDU) used on many Airbus airplanes. The MDDU
uses 3.5 inch floppy disks for uploading, downloading, and data storage.
 a Data Loader Selector (DLS) is used to select the system where data should be
loaded to or from.
*Located on aft
overhead panel.
 Aircraft printers typically conform to ARINC Standard 744A, which gives technical
requirements for such printers.
 A standard resolution of printing is 300 dots per inch (dpi)
 Inside the printer, an electric motor is used to advance or 'Slew' the paper.
 The printer uses a thermal print head, and the paper is heat sensitive.
 Aircraft printers receive input from CMCs, the ACARS system, and other sources by
means of data lines, which may be ARINC 429 buses or Ethernet cables. Some
printers are capable of receiving input wirelessly, and operated as part of a
wireless LAN (local area network).
 Aircraft operators are required to monitor all FCS on their aircraft.
 DTIs are inspections focused specifically on fatigue critical structures.
 An on-board structure health monitoring (SHM) system utilizes sensors deployed at
key points on the airplane structure. Strain sensors are bonded to a critical point on
the structure. If the structure at that point becomes deformed, the strain sensor also
becomes deformed. This deformation changes the electrical characteristics
(typically the resistance) of the sensor indicating that damage, stress or strain is
evident in the structure.
 The ultrasonic method uses a series of ultrasonic radiating elements and receiver
sensors attached to the airplane structure