A. Purpose of the Maintenance The purpose of the onboard maintenance is to provide
maintenance personnel with an aid to fault diagnosis further to a complaint of the crew.
To accomplish this goal:
(1) Each system includes a Built-In Test Equipment (BITE) used for detection and isolation of
faulty equipment. Furthermore the system is able to initiate tests for the purpose of
confirming a fault condition or checking that proper system operation is restored after
corrective action. Remark: To simplify the task of maintenance personnel: · The faces of the
computers and the maintenance test functions have been standardized · The maintenance
messages are displayed in clear English language and always concern the faulty component
or, in some cases, the faulty system.
(2) A Central Maintenance Computer (CMC) acquires and processes (completes, correlates,
memorizes and presents) the data transmitted by the BITEs and the warnings which have
originated the crew complaint.
(3) The result of fault diagnosis is: · Displayed to the maintenance operator through the
Multipurpose Control and Display Units (MCDU) and the Printer which constitute the user
interface. · Sent to the main base: . via the Management Unit (MU) of the Aircraft
Communications Addressing and Reporting System (ACARS) (optional system) . or via the Air
Traffic Service Unit (ATSU) (optional system) · Sent on a disk.
B. Conditional Maintenance Operation
(1) Indicating/Dispatching The flight crew as operator, take over the aircraft solely on the
basis of information available in the cockpit. The flight crew shall refer to Flight Crew
Operating Manual (FCOM) for corrective actions in the case of an abnormal event. Such an
event must be entered in the LOG BOOK. The flight crew can elect to dispatch the aircraft by
referring to the Master Minimum Equipment List (MMEL) (GO, NO GO, GO IF conditions) and
taking into account the status of the cockpit displays.
(2) Corrective action Depending on the failure criticality, the aircraft may continue to fly to
return to its main base but aircraft flight safety must not be endangered. The maintenance
crew shall then identify the failed component (item of equipment, wiring element...) on the
basis of the log book report, repair or replace it. To this end, the maintenance crew uses the
data of the log book, the aircraft maintenance documentation (IPC, TSM, AMM, ASM, AWM,
AWL,...) and the required tools. The operator can then perform the necessary adjustments,
check the correct operation of the system (cockpit display status clearance) and declare the
aircraft "fit for service".
B.
Levels of Maintenance The failure information delivered by the Central Maintenance System
(CMS) corresponds to several levels of maintenance.
(1) Line maintenance This maintenance is characterized by rapid intervention of
maintenance personnel in a short time period; it is limited to the isolation and replacement
of a faulty equipment. This action consists of the identification and/or confirmation of fault
condition(s), the isolation of the fault and the replacement of the faulty unit (i.e the Line
Replaceable Unit (LRU)). A test is carried out before and after the removal/installation
procedure to check the correct operation of the system.
(2) Hangar or main base maintenance This maintenance is characterized by intervention of
maintenance personnel in a longer time period and generally concerns actions that cannot
be performed at line maintenance level, either because the procedures are too lengthy or
because more skilled personnel are required.
(3) Workshop maintenance These maintenance actions are performed at regular intervals
(as defined by the Operator Maintenance Program (OMP)). Intervention of maintenance
personnel is then scheduled according to aircraft utilization and concerns the items of
equipment for which some mechanical parts are not monitored and/or tested. These failures
are called hidden failures.
D.
Various Failure Classes (Ref. Fig. CMS - Failure Classification SHEET 1) The failures detected
by the system BITEs are classified in 3 categories (class 1, 2, 3) with respect to their
consequences on aircraft safety and availability. For a given failure with given operational
consequences, the MMEL indicates to the pilot whether the aircraft may continue to fly or
not according to 3 criteria:
· GO criterion: the aircraft may continue to fly without restriction
· GO IF criterion: the aircraft may continue to fly under certain conditions (e.g.: a test must
be performed, the information is available from another equipment, weather conditions...)
· NO GO criterion: the aircraft may not continue to fly. This implies mandatory intervention
of maintenance personnel before releasing the aircraft into service.
(1) Class 1 failures These are failures detected by the systems, which may have an
operational consequence (safety aspect) on the current flight. Some are indicated in the
cockpit, and others in the cabin. These failures are indicated to the crew in flight in the
cockpit: · By messages (level 1, 2, 3) on the Engine/Warning Display (EWD) · By flags on the
Primary Flight Display (PFD) or the Navigation Display (ND) or the System Display (SD) · By
local warnings. These failures are indicated to the crew in flight in the cabin: · By messages
on the Forward Attendant Panel (FAP) · By caution lights · By chimes.
(2) Class 2 failures These are failures detected by the systems, which do not have
operational consequences (safety aspect) on the current flight or on the next flights but
which may have consequences if a second failure occurs. These failures are indicated on
ground by an Electronic Centralized Aircraft Monitoring (ECAM) report after shut down of
the engines.
(3) Class 3 failures These are failures detected by the systems, which have no consequences
on aircraft safety or availability. These failures are not indicated to the crew (no cockpit
event). They can be left uncorrected because they are not time limited. In the FADEC BITE,
the Scheduled Maintenance Report also contains faults without cockpit event, but which
should be corrected within a delay specified in the Maintenance Planning Document. These
faults are identified by a specific class SM (Scheduled Maintenance).
E.
Internal and External Failures Independently of the failure classification, for a given system, a
failure is either internal or external to the system. A system is made up of a group of
removable components called LRU which are specific to the system and which are said
"internal to the system". Each LRU is a component which is internal to a given system and
not to another. In many cases, a system uses data from other systems which can be
considered as sensors and which are said "external to the system". The system BITE is
activated whenever a failure affecting the operation occurs, whether the failure is internal or
external to the system.
Example: a pressure sensor used by several systems is taken into account as an internal
component by only one of these systems.
PFR Definition and Presentation:
The purpose of this item which is part of the main maintenance menu is to display in flight or on
ground:
· the warning messages which are displayed or not displayed on the Engine/Warning Display (EWD)
(red WARNING and amber CAUTION) and the name of the systems declared failed in the
MAINTENANCE item on the STATUS page of the System Display (SD) (the CMC adding the mention
MAINTENANCE STATUS to the equipment name, e.g. APU --> APU MAINTENANCE STATUS) during
the last flight leg or the current flight leg
· the fault messages (class 1 and 2) concerning all the systems and which appeared during the last
flight leg or current flight leg.
· the flags and advisories displayed by the DMCs on the display units and add in the PFR the
corresponding messages in the cockpit effects column. Only the red flags on the PFD, ND and the SD
advisories are dealt with. The warning, fault, flags and advisories messages can be filtered.
NOTE: Warning-fault correspondence and display. The warnings and faults are displayed in the order
of acquisition by the CMC, minute after minute. The last fault or the last warning memorized is
displayed first. The faults or warnings which follow are displayed in succession in a chronological
sequence.
1 Description of the entire report
1 = Flight phase number acquired
2 = Flight phase in plain English
01 = Power-On
02 = Engine Start
03 = Taxi Out
04 = Take-off Roll
05 = Climb
06 = Cruise
07 = Approach
08 = Rollout
09 = Taxi In
10 = Engine Shut Down
3 = UTC of warning or fault reception (when a warning and a message are correlated, UTC of fault
message is displayed)
4 = FWC computed warning message (label 357)
5 = "Not Displayed" if the warning has not been presented
6 = ATA REF of warning transmitted by the FWC (label 357)
7 = "ATA" is displayed if one ATA number exists
8 = "NO" if the report contains no warning message or total number of warnings memorized in the
report
9 = aircraft identification parameter
10 = date at leg opening
11 = flight number parameter
12 = departure and arrival airport parameter
13 = UTC of START OF LEG/END OF LEG
14 = printed report name · "POST FLIGHT REPORT" · "CURRENT FLIGHT REPORT" · "PREVIOUS FLIGHT
REPORT"
15 = leg number 00 for POST FLIGHT REPORT and CURRENT FLIGHT REPORT and leg number 01, 02,
03,....... for PREVIOUS FLIGHT REPORT.
16 = 1 or 2 to indicate which CMC printed the report
17 = page numbering
18 = date at printing activation
19 = time at printing activation
20 = "NO" if the report contains no fault message or total number of faults memorized in the report
21 = "Source" is displayed if a fault exists
22 = indicates the source which transmitted the fault, a star * is shown facing the source if it is
affected by a class 2 fault
23 = "Identifiers" is displayed if at least one identifier exists for the fault
24 = name of identifiers (max. 6), a star * is shown facing the name of the system if the correlated
message is a class 2 fault.
25 = "ATA" is displayed if the fault message is present
26 = ATA REF of the fault
27 = "Class" is displayed if the fault message is present
28 = fault class number
29 = "Intermittent" if the fault is intermittent or "Hard" if the fault is hard
30 = text of the fault message
31 = "END OF REPORT" if last page or "CONTINUED" if the report contains several pages
32 = "DB/N" is displayed followed by the identifiable number. These two are displayed when POST
FLIGHT REPORT is filtered.
(4) PREVIOUS FLIGHT REPORTS
(a) Definition The purpose of this item, which is part of the main maintenance menu, is to display on
the ground only, the warning, fault, flags and advisories messages concerning all the systems, which
occurred during the preceding 64 flights (failure history). It is limited to 252 warning or fault
messages (the number of preceding flights can thus be less than 64 flights). This item is the sum of
the POST FLIGHT REPORT items over several flights. The warning, fault, flags and advisories
messages can be filtered. The PREVIOUS FLIGHT REPORT will be presented with the correct data
base number (which may differ from the POST number).
(b) The current flight leg (CURRENT FLIGHT REPORT) is numbered 00 and the last recorded flight leg
(POST FLIGHT REPORT) is numbered 00 but are not shown in this item. The preceding flight legs
(PREVIOUS FLIGHT REPORTS) are numbered and shown on the MCDU in decreasing order: 01, 02...,
63.
In the event of a flight without failure, this flight is taken into account for the counting but is not
shown on the PREVIOUS FLIGHT REPORTS. Remark: in the event of a computer removal/installation,
two cases may be present:
· either the new computer has been used on another aircraft which made several flights. The flights
memorized in the PREVIOUS FLIGHT REPORTS are not shown on the MCDUs because the aircraft
identification of the memorized flights differs from the identification of the aircraft on which the
computer is installed. The next flights are memorized one after the other and made available on the
MCDUs.
· or the new computer has a blank memory. Consequently, a memorized flight difference exists
between the two computers (for example the flight - 12 of the unchanged computer corresponds to
the flight - 00 on the new computer).
POST FLIGHT REPORT with the message FIRST A/C INSTALLATION is artificially created by the CMC to
indicate the date of computer installation on aircraft to the maintenance operator.
(5) AVIONICS STATUS (a) Definition The purpose of this item, which is part of the main maintenance
menu, is to display in flight or on ground (in fact data are refreshed after each scanning of inputs),
the identity of systems affected by a Class 1 or 2, internal or external fault at the time when this
function is executed.
(6) SERVICING REPORT
(a) Definition The purpose of this item, which is part of the main maintenance menu, is to provide, in
flight or on ground, a report of different parameters involved in periodic checks which might lead to
a servicing action. The servicing report is accessible on the MCDU, printable on the airborne printer,
transmittable through ATSU and downloadable to the data loader. It is possible to add information
texts in each coupon format or in the complete servicing report format. It is also possible to define
the titles of the complete servicing report and the summary item coupon, in order to enable an
airline to rename for instance the summary item coupon: "ETOPS service check" in case of ETOPS for
the aircraft. The information texts and titles are defined on the ground on a PC, and uploaded in the
CMC through a disk and a data loader.
The CMC processes uploadable customizable servicing thresholds in order to trigger if necessary, the
printing or the transmission of the servicing item which includes the corresponding parameter for
which a servicing action is thus required. The servicing thresholds concern only the numerical
parameters of the servicing report (oil quantity, water tank level, etc...). These thresholds are
defined by the airline maintenance engineering on a PC and stored in a disk. These data are then
uploaded through a data loader into the CMC. The same procedure is used for updating the servicing
thresholds which depend on the aircraft use and the airline maintenance policy. For each numerical
servicing parameter, minimum and maximum thresholds can be defined.
The servicing report is composed of the different items listed below:
· engines
· IDG
· APU
· hydraulic
· fuel
· landing gear
· oxygen
· door and slide bottles
· water/waste
· air conditioning
(b) Servicing report triggering processing The purpose of the triggering processing is to print or
transmit only the servicing report item including a parameter which needs an action and has thus to
be provided to the user.
The servicing report consists of 11 MCDU pages. The servicing report which is displayed on MCDU is
only "complete" and therefore includes all parameters. Indeed the MCDU is only used as a back up
means for checking the servicing report.
(d) Description of the displays
1 Servicing report parameters The servicing report includes parameters concerning different ATA in
specific items. The parameters are displayed or printed at each function activation, several cases
are possible:
· Parameters available but not meaningful (example: engine oil level while engine running) These
parameters are displayed. The airlines have the possibility to inform in clear language in the
downloadable customizable information texts format, when these parameters are meaningful (for
instance, the engine oil levels are meaningful approximately 10 mn after engine shutdown).
· Parameters not available due to failure of the source system, or if it is not powered In this case,
characters or digits of these parameters are replaced by dashes: "-", and the corresponding servicing
coupon is automatically printed 10 min after the last engine shutdown in case of "coupon mode"
selection.
· Parameters available and exceeding a customizable servicing threshold (above a maximum or
below a minimum threshold) The corresponding servicing item is automatically printed or
transmitted according to the selection (triggering process or no triggering process) through the
report programming function, 10 min after the last engine shutdown. This item is also included in
the "coupon mode" servicing report which is printable or transmittable on manual request.
· Parameters not available because they correspond to optional equipment which is not installed The
CMC processes this case and deletes the corresponding parameters from the servicing report or the
corresponding servicing coupon.
(7) UTC/DATE INIT
(a) Definition In flight or on ground, after a long power interrupt affecting both CMCs (more than 5
s), if the clock is not available, the UTC/DATE INIT item is added in the CMC menu. This item enables
the crew to initialize the time and date, from the MCDU keyboard.
(8) CLASS 3 REPORT
(a) Definition The purpose of this item, is to display the Class 3 faults transmitted by all the systems
connected to the CMC. This report is generated in the CMC upon operator's request.
(9) AVIONICS CONFIGURATION REPORTS
(a) Definition The function of this item (which is a part of the primary maintenance menu) is to show
a set of configuration information available in each BITE menu item known as the LRU
IDENTIFICATION (on the ground only). This item is available only with CMC1. Because of the
specified software components (which are numerous), a special report is made for the management
of the software components and databases of the related equipment.
A. Systems and Related BITEs
(1) BITE definition:
Each aircraft system includes a device which detects, isolates and memorizes faults and which is
called a BITE. The BITE characteristics are:
· the detection of any fault affecting a system · the identification of the fault at the level of the Line
Replaceable Unit (LRU). A failed LRU is identified by its ATA 100 reference, its designation and in
most cases, by its Functional Item Number (FIN)
· the distinction between faults at system level (internal faults) and faults at aircraft interface level
(external faults)
· the memorization of the necessary maintenance information. The memorization logic is such that
information memorized in flight is not affected by ground operations, such as trouble shooting,
check list, power interruption or cut off, etc. A flight/ground information enables different memory
sections to be used (flight memory, ground memory)
· the transmission of the maintenance data to the CMS · the dialog with the CMS for the test
functions.
(1) Case of the Type 1 systems:
These systems form the largest group.
(a) Hardware interface A type 1 BITE system is characterized by an input/output interface of the
ARINC 429 BUS/ARINC 429 BUS type.
(b) BITE characteristics These systems have the capacity to memorize data concerning the faults
detected over a maximum of 64 flights. The system BITE ensures permanent transmission on its
output bus of the memory section concerning identity of the LRUs declared failed during the last
flight.
(c) There are 3 types of configurations for type 1 systems
· single computer
· BITE concentrator computer The Fault Isolation and Detection System (FIDS) is used as a system
BITE (maintenance data concentrator). The FIDS is connected to the CMS for data acquisition and
reception; it is also connected to the BITEs of the various system constituents. It receives commands
from the active CMC, interprets them and transfers them to the other BITEs of the concerned
systems. It receives the incorrect operation statuses of the component BITEs, consolidates the BITE
diagnosis and generates a fault message which is sent to the CMCs.
· Dual computer A dual computer includes two different sub-systems in the same computer.
Upon selection of the system by the operator (from the MCDU), the system BITE transmits the
content of its menu on its output bus. For these systems the basic functions are:
· LAST LEG REPORT: The purpose of this item is to present, on the ground only, the internal and
external fault messages concerning this system, that appeared during the last flight. These fault
messages contain the name of the faulty LRU associated with the time at which the fault occurred,
the fault class (1 or 2) and the ATA reference. If no fault is detected during the last flight, a NO FAULT
DETECTED message is displayed in the center of the screen.
· PREVIOUS LEG REPORTS: The purpose of this item is to present, on the ground only, the internal
and external fault messages concerning this system, that appeared during the previous 64 flights.
This item is the sum of the LAST LEG REPORT items over several flights. These fault messages contain
the name of the faulty LRU associated with the time and date at which the fault occurred, the fault
class (1 or 2), the ATA reference and flight number (1 to 64). The aircraft identification is also
included in the header.
· GROUND REPORT: The characteristics of this item are the same as those of the LAST LEG REPORT.
This item contains the internal fault messages that appeared when the aircraft was on ground (e.g.
actuation of the circuit breaker resulting in a system fault).
· TEST: The purpose of this item is double: · initiation of a system test (there may be several) from
the MCDU · display on the MCDU of the test results. If the test duration is more than 1 s, TEST IN
PROGRESS XXS (XX represents the approximate maximum waiting time in seconds) is displayed in
the center of the screen. If the test is OK, the TEST OK message is displayed in the center of the
screen. If the test is not OK, a fault message is displayed, giving the name of the faulty LRU, the ATA
reference and the fault class (1, 2 or 3).
· LRU IDENT: The purpose of this item is to present, on the ground only, the part number of the
selected system. The serial number and the data base number can also be indicated by certain
systems
· TROUBLE SHOOTING DATA: The purpose of this item is to present, on the ground only,
complementary data concerning the faults. These messages contain the date and time of the
message presented in clear, data constituting a snapshot of the system environment at the moment
of the fault, or contain parameters internal to the computer, presented in encoded form (e.g.
aircraft configuration, valve position etc.).
· CLASS 3 FAULTS: The purpose of this item is to present, on the ground only, the Class 3 fault
messages concerning this system and present during the last flight. These fault messages contain the
name of the equipment affected by a Class 3 fault associated with the date. The time and the ATA
reference can also be presented.
The optional functions are:
· GROUND SCANNING: The purpose of this item, on the ground only, is to reconfigure the computer
BITE as being in flight, in order to analyze the internal and external fault messages that appeared
during the last flight, and which are still present when the request is made (i.e. on the ground).
These fault messages contain the name of the faulty LRU associated with the time and date at which
the fault occurred, the fault class (1 or 2) and the ATA reference. A prompt > is present for each
message, enabling access to the TROUBLE SHOOTING DATA item for the selected fault. NOTE: The
ground Scanning function can be used as an additional mean to track intermittent faults and to
confirm faults on ground
· SPECIFIC DATA: If only one type of specific data exists in the system, the exact name is displayed in
place of SPECIFIC DATA (e.g. in the fuel system, INPUT PARAMETERS VALUES is displayed). If more
than two types of specific data exist in the system, an action on the line key adjacent to the SPECIFIC
DATA title enables a sub-menu to be displayed.
(2) Case of the Type 2 systems:
(a) Hardware interface A type 2 BITE system is characterized by an input/output interface of the
discrete/ARINC 429 BUS type.
(b) BITE characteristics These systems have the capacity to memorize data concerning the faults
detected on the last flight. The system BITE ensures permanent transmission on its output bus of the
memory section concerning the identity of the LRUs declared failed.
Unlike the Type 1 systems, there is no menu mode for the Type 2 systems. These functions are
presented on the MCDU by the CMC (pseudo Menu mode). Upon selection of a system by the
operator (from the MCDU), the active CMC displays the menu of the selected system and presents
data on the MCDU. These functions have the same content as the Type 1 systems. For these
systems, the basic functions are:
· LAST LEG/GND REPORT
· CLASS 3 FAULTS
· TEST
· LRU IDENT.
(3) Case of the Type 3 systems:
(a) Hardware interface A type 3 system is characterized by an input/output interface of the
discrete/discrete type.
(b) BITE characteristics All systems indicate their status (correct or incorrect) further to a test
request. Some systems also indicate their status in a permanent manner:
· TRs
· ICE DETECTORS (if installed)
· PAX OXY (if installed)
· DLRB-DLS (if installed)
The system BITE ensures transmission on its output discrete, of the correct or fault operation
information. From this information, the CMC encodes the fault message in plain language if a fault is
present.
For these systems, the only possible function is the TEST function or the RESET function. There is no
menu mode for the Type 3 systems: these functions are presented on the MCDU by the CMC. Their
establishment mode differs from the Types 1 and 2. The TEST or RESET function is established using
data only available after execution of the test or the reset (not memorized by the BITE) that are
transmitted by the system to the CMCs during a certain time (a few hundred ms) on its output
discrete. When these functions are selected by the operator, the active CMC initiates the test or the
reset via the "active CMC --> system" discrete then reads the result on the "system --> CMCs"
discrete and generates a message (correct operation or fault) on the MCDU.
(4) Some systems are special conditions:
· Printer The hardware interface is of type 1 system and the BITE characteristic is of type 2 system.
· MDDU (if installed) The hardware interface is of type 1 system and the BITE characteristic is of type
2 system.
· HUDC (if installed) The HUDC is of type 2 system without the discrete input.
· PAX OXY (if installed) It is of type 3 system without the discrete input. This system makes sure that
the permanent transmission on the three output discretes of the correct or incorrect operation
information.
· PVIS (if installed) It is of type 1 system without the ARINC BUS output. PVIS link is mono-directional
and from the CMC output to the PVIS input only.
CMC:
The two CMCs are identical and interchangeable. All the type 1, 2 and 3 system inputs (ARINC 429 or
discrete) are connected to the two CMCs for transmission of the maintenance data and of the
aircraft general parameters.
Note: The interconnection of both computers differs on the points below:
· a discrete permits to give the physical position of the CMCs in the aircraft (side 1 and 2)
· a pushbutton switch in the cockpit (discrete) causes switching of the relays in the CMC 1. If
pushbutton is OFF, CMC 1 is master. If pushbutton is ON, CMC 2 is master.
Links between CMC 1 and CMC 2:
2 ARINC 429 High Speed (HS) buses link the two CMCs. This network is called CROSS TALK (X-TALK)
and enables both CMCs to exchange general data (Remark: moreover, for each CMC, the opposite
CMC is considered as a full system BITE) ·
2 discretes link both CMCs (one in each direction) in order to give the status of one computer with
respect to the other (master or slave) ·
9 ARINC 429 Low Speed (LS) buses link the CMC 2 to the CMC 1 enabling dialog of systems with the
master CMC 2 in the event of CMC 1 fault or manual switching.