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M11.18 Overview: On Board Maintenance System

• The lecture is on the On Board Maintenance System (OBMS) with reference to ATA 45

Content Covered

• On Board Maintenance Systems (ATA45)
• Central maintenance computers
• Data loading systems
• Electronic library systems
• Printing
• Structure monitoring (damage tolerance monitoring)
• Health Usage Monitoring System

Acquisition of System Data

• A/C system data acquisition is achieved through four major electronic systems
• ECAM monitors operational data for warnings in normal and abnormal situations
• FDRS (Flight Data Recording System) is mandatory, recording A/C operational parameters for incident investigation
• CMS (Central Maintenance System) monitors various systems' BITE data to record system failures
• ACMS (Aircraft Condition and Monitoring System) records significant operational parameters to monitor engines and analyze A/C problems

Information Retrieval Methods

• Information can be retrieved through ECAM displays, MCDUs, and the printer
• Retrieval is possible via the Air Traffic Service Unit (ATSU) to a ground station using the Aircraft Communication Addressing and Reporting System (ACARS) function
• The downloading system and the recorders can also retrieve information

Maintenance Operation Analysis

• Maintenance operations divide into Short-term troubleshooting, In-depth troubleshooting, and Long-term maintenance
• Short-term troubleshooting utilizes ECAM and CMS through MCDUs, printed or ATSU down-linked reports via ACARS
• In-depth troubleshooting uses CMS and ACMS via MCDUs and printed/downloaded reports
• Long-term maintenance employs ACMS and FDRS ATSU down-linked/downloaded reports or recorded data

On Board Maintenance System (OMS)

• The purpose of an Onboard Maintenance System (OMS) is to assist in troubleshooting and maintenance of an integrated digital avionic system on an aircraft
• OMS is also known as Central Maintenance Computing System (CMCS)
• OMS in use in modern aircraft, range from a simple magnetic indicator on an LRU, to complex systems that allow engineers to connect laptop computers to download system parameters and fault data
• The integrated avionic system incorporates a support tool known as 'Integrated Maintenance Test' (IMT). It tests the system/subsystems, detects faults stored in the fault warning computer, allows to download fault reports for analyzing with special equipment (analysing software)
• OMS allows: troubleshooting of systems & subsystems; systems testing via Integrated Maintenance Test (IMT); provides: fault codes & download functions for fault recordings

Onboard Maintenance System Composition

OMS usually comprises:

• Central Maintenance System (CMS) for centralizing operational and maintenance data. CMS can exchange data with operation ground center upon request
• Data Loading and Configuration System (DLCS) to manage software updates in both computers and onboard database
• Aircraft Condition Monitoring System (ACMS) to acquire and process aircraft operational data for preventive maintenance

Built-In Test Equipment (BITE) Functionality

• A BITE system is used to monitor & detect faults in a variety of aircraft systems.
• BITE systems reduce time spent on fault finding and eliminate need for specialist test equipment.
• BITE continuously tests systems, stores fault info for later recall by flight crew/maintenance team
• Fault info is stored in non-volatile memory in the equipment or the Central Maintenance Computer (CMC).
• After repair, the BITE system can reset the system via the Maintenance Access Terminal, Portable Maintenance Access Terminal (PMAT), or Control and Display Unit (CDU).
• Most BITE systems can isolate system faults with at least 95% probability of success on the first attempt
• Most BITE systems perform Operational Test and Maintenance test

Operational BITE Program Checks

• Operational BITE programs check Input signals
• Protection circuitry
• Control circuitry
• Output signals
• Operational BITE circuitry
• During normal system operation BITE monitors for a "Watchdog" signal
• The "Watchdog" routine detects hardware failure/signal distortion which may create an operational fault
• If either condition is detected, BITE program provides isolation and initiates warnings, records in non-volatile memory

BITE Initiation Forms

• Power up BITE (PUBIT) or Start up BITE
• Interruptive BITE (IBIT) or Initiated BITE
• Continuous BITE (CBIT)

Power up BITE (PUBIT)

• PUBIT's ability to detect resident failures in the system is limited.
• PUBIT initiates upon initial power supply to the aircraft system.
• PUBIT checks condition of power supplies, phase rotation, frequency, and voltage.
• PUBIT also carry out checks of the processors and the RAM, ensuring proper function
• Through BIOS, PUBIT invokes the loading of the operating and airline modifiable software. It then transmit status to the aircraft's main computer for display or record

Interruptive BITE (IBIT)

• IBIT is initiated by ground crew or pilots
• In its simplest form, it's a press-to-test, but more complex with On-Board Maintenance Systems.
• It is done by first disconnecting the inputs and outputs of the computer electronically.
• BITE systematically injects a signal into each channel/lane, looking for the expected output across the system's design range
• If the output is not within limits, a status and fault code are generated and sent to Flight Warning Computer (FWC) and OMS
• Interruptive BITE, also called ground test or initiated test

Continuous BITE (CBIT)

• CBIT runs continuously at set intervals during system operation
• Inside the Line Replacement Unit (LRU), there are two channels (command,monitor) to provide outputs; three channels feature a standby
• All channels receive input signals and calculate the output solution
• The command channel produces an output signal, the monitor checks if the command channel works correctly; errors will send status to Aircraft Flight Warning Computer FWC & OMS
• If there is an error it is displayed or recorded.

Defect Categorization

• Defects are categorized by their effect: Immediate Effect, which should be cleared ASAP; Delayed Effect, which requires moderately speedy repair; and No Effect, which can be cleared on the next hangar schedule visit

BITE Failure Categories

• Failures detected by the BITEs are in Class 1, 2 and 3 with respect to their consequences on aircraft safety and availability
• MMEL indicates to the pilot whether the aircraft may continue to fly or not according to Go criteria, Go if criteria, and No go criteria
• Go criteria: the aircraft may continue to fly without restriction
• GO IF criteria: the aircraft may continue to fly under certain conditions (e.g.: a test must be performed, the information is available from equipment, weather conditions…)
• NO GO criteria: the aircraft may not continue to fly. This implies mandatory intervention of maintenance personnel before releasing the aircraft into service

BITE Failure Categories (Class 1 & 2)

• Class 1 failures: failures detected by the systems, which may have an operational consequence (safety aspect) on the current flight. These failures are indicated to the crew in flight by Messages, Flags, and Local warnings
• Class 2 failures: failures detected by the systems, which do not have operational consequences but which may have consequences if a second failure occurs. These are indicated on ground by an Electronic Centralized Aircraft Monitoring (ECAM) report after shutting down of the engines.

Central Maintenance System (CMS) Overview

• The CMS is a centralized BITE system forming the basis of all On-Board Maintenance Systems
• Boeing: Central Maintenance Computer (CMC)
• Airbus: Centralized Fault Display System (CFDS)

Onboard Maintenance System (OMS) LRU Composition

• A system comprises computers, sensors, actuators, and probes.
• The computer system's function in this instance is to be detect errors, it is called the Built-In Test Equipment (BITE).
• During normal use, the system is constantly checked for fault detection, isolation, and memorization

CMS Operational Modes

• Normal Mode: Acquire aircraft system continuous monitoring data, failure detection report and Built-In Test Equipment (BITE)
• Interactive Mode: Provides system testing, accessing recorded maintenance data, fault codes, and download functions
• CMC1 and CMC2

Aircraft Field Loadable Software (FLS) & Database Field Loadable Data (DFLD)

• The data is a data file on the hard drive or on a disk in the disk drive
• Aircraft Field Loadable Software (FLS) is software which is executable code loaded without removing systems/equipment from the aircraft
• A maintenance mechanic/technician typically loads FLS onto a aircraft system following defined maintenance manual procedures
• FLS is configured as a component to the target hardware (effects the part number of target hardware)

FLS Types

• There are Loadable Software Aircraft Part (LSAP) which provides FLS that needs to meet regulatory requirements for airworthiness/operation. Such is not a component of the hardware, but an approved aircraft design, therefore, an aircraft part, which needs released documentation
• User modifiable Software (UMS) is declared by the aircraft's design organization as modifiable by the operator without CAA review.
• Option Selectable Software (OSS) which is LSAP that contains approved,validated components and combinations of components activated/modified by the operator w/in TC/STC holder boundaries

DFLD Definition

• Refers to data loadable into target hardware databases
• Database is an embedded item that resides inside the target hardware and which is not field loadable
• A Data File contains the actual data for field loading database

Failure Condition Level - Descriptive Summary

• Level A (Catastrophic): Failure could lead to a crash
• Level B (Hazardous): Large negative impact on ability for safe conditions, performance, operation of the plane
• Level C (Major): Significan but less of an impact than A or B (leads to discomfort over injuries)
• Level D (Minor): Failure is noticeable (leads to inconvenience)
• Level E (No effect): No impact

Maintenance Access Terminal (MAT)

• Provides Access to the CMCS and airplane condition monitoring system (ACMS)
• Components: MAT/cursor control device, chassis, display, floppy/hard disk drive, flash memory module
• Display is a liquid crystal display (LCD) which provides the graphical user interface, The disk drive loads data and enables downloading

MAT Key Functionality

• The Cursor Control Device (CCD) enables the operator to move the cursor
• The Chassis houses all the components.
• The Chassis has a procesor with the Maintenance Terminal Function (MTF), the MAT flash memory module stores MTF software
• Comes suppied with keyboards, controls and alternate keyboard

Portable Maintenance Access Terminal (PMAT)

• Portable Maintenance Access Terminal (PMAT): a modified laptop for aircraft use
• Enables remote access for operator, to CMCS and ACMS
• Main equipment centre, Nose wheel well, Right main wheel well and Jack screw area
• Interfaces into flight deck

Flight Deck Effect (FDE) Explanation

• Flight Deck Effect (FDE) includes Engine Indicating Crew Alert System (EICAS) messages, Primary Flight Display (PFD) flags, Navigation Display (ND) flags, and Scheduled Maintenance Tasks
• Ground crew must find the cause and take corrective action; use the Fault Isolation, Aircraft Maintenance Manuals
• Maintenance Messages supply detailed fault data; if there is a fault, it reports to the CMS

FDE Processing

• When an FDE occurs and the CMCS receives a maintenance message with a relation to the FDE, the CMCS correlates the FDE to the message
• Maintenance Access Terminal (MAT) communicates with the CMCF in the Airplane Information Management System (AIMS); 2 optic fibre interfaces provide connections to Local Area Network AVLAN are part of OLAN
• The PMAT connects to a Server Interface Unit (SIU) which perform a bridging function
• Maintenance Team provides information from Maintenance Access Terminal MAT + portable versions

Terminology: Status Message

• A Status Message gives engineers system failure indications on status display.
• For dispatch, should not be present

Terminology: Maintenance Message

• Set by CMC when fault exists.
• Used per ATA Chapter.
• Not displayed to aircrew, only engineers or maintenance crew for aircraft rectification

Terminology: Fault Code

• Set by the failed LRU/CMC.
• Helps for correlating info, not given to crew.
• Engineers use for diagnosis, get code.

Terminology: Fault Correlation

• Links FDEs & maintenance messages.
• Maintenance correlates FDE with a CMC-generated message.

Data Loading Systems

• CMCF supplies loading formats on MD units so maintenance select the source+ data location

Electronic Library System

• The System is part of the Onboard Information System (OIS)
• A set of electronic documentation includes data on cabin and operations

Printing Functionality

• Flight deck printer creates high-speed text copies for display system, condition/maintenance computing systems.
• Print driver partition data from DCMS.
• DCMF is airplane IMS +sends to DCMF.
• DCMF prioritizes data being sent to printer as FDCF and Airplanes Conditions

Structure Monitoring (ACMS)

• Aeroplane condition monitoring system (ACMS) aims to Collect data, Monitor performance, Record conditions, and Distribute data
• ACMS reports used for trend analysis
• Trend analysis, then rate is judged by engineering

ACMS Reports and the Aeroplane Condition Monitoring System

• ACMS reports are used for aerplane system trend analysis.
• DMU, data managment unit unit is the main component of condintion monitoring system
• DMU collects and formats reports including to, Quick Access recorder (QAR) and control display unit (CDU)

Data Management Unit (DMU) Details

• Provides a powerful data processor, allowing customization and data management
• Is programmed to monitor critical data output as it passes to other data systems/ aircraft

Data Management Unit Capabilities

• Capable of channelling reports:
• Multifunction Control Display Unit (MCDU)
• Cockpit printer
• Optical/Wireless Quick Access Recorder (OQAR/WQAR)
• ACARS

Standard Reports by ACMS details

• Weather/Position, Turbulence, Turbulence Inspection, Wind Factor, Max Operating, Engine Start, Engine Aborted Start and Inflight
• Engine Perform
• Oil Mon
• OverweightInspection, Flight Summary

Health and Usage Monitoring System (HUMS) General

• Health and Usage Monitoring System (HUMS) seeks to improve airworthiness of helicopters and air safety
• By detected, diagnosed operation
• Constantly checks for failures using data, processed by staff/flight for proper means of intervention

Main HUMS Functions

• Prompt detection of damaged area
• Logbook
• Data diagnostics