The Maintenance concept of Airbus A320 Family Aircraft is based on the use of the Centralized Fault Display System (CFDS) and Trouble Shooting Manual (TSM).

There are two levels of maintenance :

  • at the line stop : removal and replacement of equipment
  • at the main base : troubleshooting

Centralized Fault Display System (CFDS)

The purpose of the Centralized Fault Display System (CFDS) is to make the maintenance task easier by displaying fault messages in the cockpit and permitting the flight crew to make some specific tests.

The CFDS directly monitors and identifies faulty Line Replaceable Units (LRUs) in the aircraft systems and displays items identified as faulty to the maintenance crew. This is essentially achieved by analysis of all cockpit events which are triggered by the monitoring of the aircraft systems.

The CFDS contributes also to avoid unjustified removals of equipment because the CFDS makes a detailed analysis to identify the responsible LRUs and to confirm that the event was actually due to a hardware failure and not an intermittent fault.

To achieve its purpose, the CFDS has several major functions which supply:

  • A maintenance Post Flight Report (PFR) which is printed at the end of each flight. The PFR allows association of ECAM warnings and CFDS maintenance messages.
  • Directly usable maintenance messages which identify faulty LRUs.
  • Access to test of the aircraft systems.


  • Centralizes and memorizes all information concerning A/C system failures.
  • Controlled by a computer called Centralized Fault Display Interface Unit (CFDIU).
  • Provides a central maintenance aid which allows from the cockpit to extract the maintenance information.
  • CFDIU receives the flight phases and ECAM warnings from the FWC.
  • The ECAM warnings are used by CFDIU to generate the LAST or CURRENT LEG ECAM REPORT. Only PRIMARY failures, INDEPENDENT failures and CLASS 2 failure messages (Maintenance status) are received.
  • CFDIU is controlled from the two MCDU to display BITE data results from the system and initiate maintenance tests.


CFDS is made up of the following components – 

  • BITEs of the systems : Each electrical or electronic system of the aircraft includes a fault detection, isolating and storing device called a BITE.
  • CFDIU : This computer is connected to the BITE of the electronic systems of the aircraft and receives the fault data from these systems.
  • MCDUs : used for the display of data and for sending commands to the systems.
  • Printer : printer is connected to the CFDIU and serves to print reports.
  • ACARS (with ATSU installed) : This system is connected to the CFDIU and serves to send reports to the ground. ACARS uses VHF3.
  • Centralized Data Loading Connector (CDLC) : It is connected to the CFDIU and enables connection of a Portable Data Loader (PDL) for Maintenance filter database uploading.


The CFDS operates in two main modes :

  • NORMAL mode or REPORTING mode (in flight)
  • INTERACTIVE mode or MENU mode (on ground)

In NORMAL mode, the CFDS records and displays the failure messages transmitted by each system BITE. In INTERACTIVE mode, the CFDS allows any BITE to be connected with the MCDU in order to display the maintenance data stored and formatted by the BITE or to initiate a test.


The Centralized Fault Display System (CFDS) identifies the faulty system and puts any failures or faults into one of three classes. The failures are classified according to their importance:


  • Class 1 failures are the most serious ones and require an immediate maintenance action subject to the Minimum Equipment List (MEL).
  • Class 1 failures have an operational consequence on the flight.
  • You can display the class 1 failures on the MCDU:
    • in the LAST (or CURRENT) LEG REPORT.
  • These faults are also indicated to the crew in flight:
    • by the ECAM system (upper and/or lower DU).
    • by local warning in the cockpit.
  • Refer to the Minimum Equipment List (MEL): “GO”, “GO IF” or “NO GO”.


  • Class 2 failures have no immediate operational consequence and can be displayed on request on the ECAM STATUS page, under the MAINTENANCE title.
  • You can display the class 2 failures on the MCDU:
    • in the LAST (or CURRENT) LEG REPORT.
  • A class 2 failure has to be repaired within 10 days. Refer to the MEL: “GO” without condition.


  • Class 3 failures have no operational consequence.
  • These faults are not indicated to the crew but you can display the name of the systems affected by at least a class 3 failure in the AVIONICS STATUS (only available on ground).
  • Do not refer to the MEL.
  • Class 3 failures have no fixed time for correction.
  • However, correction is recommended to improve the dispatch reliability.
  • Class 3 failures may be corrected during the A CHECK programmed maintenance operations.


  • Most systems are type 1 systems.
  • Type 1 systems can memorize failures, which occurred in the last 64 flight legs.
  • Type 2 systems memorize only failures from the last flight leg.
  • Type 3 systems cannot memorize failure messages.


The main functions of the CFDS are :

  • Obtaining and storing messages transmitted by the connected system BITEs, or by the Flight Warning Computer (Warning and Caution titles)
  • Detailing the maintenance phases.
  • Presenting maintenance reports :
    • Last leg report
    • Last leg ECAM report
    • Previous leg report
    • Avionics status
    • System report test
    • Post-flight report.


On ground, all the functions are available. In flight, only CURRENT LEG REPORT and CURRENT LEG ECAM REPORT are available.


  • internal fault messages (class 1 and 2), concerning all systems, occurred during the last or the current flight.
  • the list of systems affected by this fault that are called identifiers.
  • On the ground, the item is presented under the title LAST LEG REPORT, in flight it is presented under the title CURRENT LEG REPORT.
  • It can store up to 40 failures.


  • warning messages (class 1 and 2 faults) displayed on the upper ECAM display unit during the last or the current flight.
  • These are the primary or independent warnings.
  • On the ground, the item is presented under the title LAST LEG ECAM REPORT, in flight it is presented under the title CURRENT LEG ECAM REPORT.
  • It can store up to 40 warnings.


  • on the ground only, the internal fault messages (class 1 and 2) concerning all systems, appeared during the previous 64 flights (fault history). This item is the “sum” of LAST LEG REPORT items over several flights.
  • At each new flight leg, the content of the LAST LEG REPORT is transferred into the PREVIOUS LEGS REPORT.


  • On the ground and in real time.
  • Identity of systems that are affected by an internal or external fault (class 1, 2 or 3).
  • (CLASS 3) is displayed next to the name of a system that is affected by at least one class 3 fault.


  • on the ground only.
  • a dialog between the MCDUs and each of the systems connected to the CFDS.
  • list of all the systems connected to the CFDS, in ATA chapter order.
  • System menus also constitute the system BITEs. (Second Function)
  • For Type 1 systems, possible functions are:
    • TEST
  • For Type 2 systems, possible functions are:
    • TEST
  • For Type 2 systems, only possible functions is :
    • TEST function


  • a single report after the flight.
  • ECAM warnings (primary and independent) and Fault Messages (class 1 and 2) of the last flight (so as to permit correlation).
  • This is the “sum” of LAST LEG REPORT and LAST LEG ECAM REPORT items.
  • Messages on PFR are separated into two parts :
    • First part contains the ECAM warnings associated with the time, the flight phase and the ATA reference,
    • Second part contains the failed LRUs associated with the time, the ATA reference and the identifiers.
  • Aircraft identification, the date, the flight time, the flight number (airline) and the departure and arrival airports are included in the header.
  • Programmed for automatic print after flight.
  • PFR Generate –
    • Beginning of PFR recording:
      • if flight number inserted prior to first engine start, first engine started + 3 minutes.
      • if not, aircraft speed > 80 knots.
    • End of PFR recording:
      • Aircraft speed < 80 knots + 30 seconds.


  • filtering all the spurious or unjustified faults/warnings.
  • is to improve the operational use of the POST FLIGHT REPORT, CURRENT/LAST LEG ECAM REPORT and LAST LEG REPORT.
  • Filter database is uploaded and activated.

Description of the PFR

Post Flight Report (PFR) is a maintenance report on the last flight that is automatically printed after touchdown, 2 minutes and 30 seconds after the aircraft speed decreases below 80 kts.

This document is the Post Flight Report (PFR). The PFR is a result of the CFDS automatic operating mode. This report is the main source of information used to initiate troubleshooting and to decide on the required maintenance actions.

The following data are recorded in the PFR:

    • the warning message available on the upper ECAM display unit
    • the maintenance status
    • These warning messages are associated with their ATA reference (aid for cross referencing with the maintenance message).
  • FAULTS : Maintenance messages are listed in the PFR in the FAILURE MESSAGES part. Additional information is associated with each message.
  • FLIGHT PHASE : Flight operational phases (CLIMB, CRUISE, etc.) are indicated in coded form in the PFR in front of the warning message. The time (GMT) is also given in front of the warning message and the maintenance message.
    FLIGHT PHASE decoding :
    • 02 : Engine start + 3 mn up to TO Power
    • 03 : TO Power up to 80 kts
    • 04 : 80 kts up to lift off
    • 05 : Climb
    • 06 : Cruise
    • 07 : Descent
    • 08 : Touch down up to 80 kts
    • 09 : 80 kts up to last engine shut down
  • ATA : This is the ATA chapter of the first suspected component. It is the entry point to the technical documentation. It may also be an aid in relation to the corresponding warning message and with the GMT.
  • SOURCE : The source is the system (for system BITE) or the computer which generated the maintenance message retained by the CFDIU for this event and recorded in the PFR.
  • IDENTIFIERs : The identifiers are the computers which have also reacted in relation to the fault by generating:
    • external maintenance messages not retained by the CFDIU
    • cockpit effects

How to Use the CFDS

System BITE

When a system includes several computers, one of the computers collects the maintenance information and provides the link between the system and the CFDIU. It then performs the BITE function and therefore reports on behalf of all system computers.

This architecture provides a better targeted diagnosis by correlating data between system computers as well as reducing bus links with the CFDIU. For the operator, the resulting consequences are minor: it is the maintenance message itself which identifies, where necessary, the message source in the system.
Example: source = ECAM1; message = SDAC1 : NO DATA FROM BMC1.
The SDAC which is part of the Flight Warning System has generated the message.

Flight/ground conditions

Information concerning detected faults is generated by the CFDS according to flight/ground conditions. Faults detected on ground may be due to maintenance actions on the aircraft and therefore are not to be taken into account (e.g. loss of a system because the circuit breaker is open). This is the reason why the aircraft systems have 2 types of memorization:

  • the first one for the faults detected on ground
  • the second one for the faults detected in flight

The flight/ground condition used by the CFDS is specific and has been selected so as to eliminate the false faults while covering, in the best possible manner, all operations. This is calculated by the CFDIU.

The flight condition is located between first engine start up plus three minutes (or eighty knots plus thirty seconds if flight plan is not available in the FMS) and eighty knots plus thirty seconds after touchdown.

In case of engine run up for maintenance purpose, a flight number (at least one character) must be entered using the MCDU to get a PFR, the eighty knots condition being never reached.

Trouble Shooting manual (TSM)

The TSM is a trouble shooting guide of all probable aircraft faults monitored and displayed by the aircraft systems. Faults not monitored by the aircraft systems are also covered.

If you cannot find a fault symptom and/or a fault isolation procedure necessary to ensure the continued airworthiness of the aircraft, or if you think that the information given is not complete, contact Airbus.

How to Use the TSM

Types of faults

In the TSM, there are two basic types of faults : monitored faults and non-monitored faults. Monitored faults are those which are monitored and displayed by the aircraft systems (mainly ECAM and CFDS). Non-monitored faults are generally not displayed by the aircraft systems and can be of a general nature, such as: “Nose landing gear doors slow to move”.

Monitored faults
  • ECAM
  • EFIS
  • CFDS
Non-monitored faults
  • Crew and/or maintenance observations.
  • Local effects.

Troubleshooting Function

  • Troubleshooting function is initiated by a logbook entry from the flight crew or maintenance crew.
  • The logbook entry serves as an entry point into the TSM using Fault Symptoms, Warnings/Malfunctions, or CFDS Fault Message, depending on the type of fault. The troubleshooter is directed to the procedure to isolate the fault.
  • The monitored faults (ECAM, EFIS) reported by the flight crew are usually associated with CFDS fault messages.
  • CFDS fault messages are used by maintenance crews. They can be displayed alone without an associated warning or malfunction, in which case they may be the entry point for maintenance-related troubleshooting. TSM entry is via the appropriate reported effect (monitored or non-monitored) or the CFDS Fault Messages using the message text.
  • Crew or maintenance observations are usually a single fault without an associated CFDS fault message. TSM entry is via fault text or keywords and ATA chapters.

Troubleshooting of Faults Reported on PFR

The following general procedure describes trouble shooting of Upper ECAM DU warnings, ECAM STS (Status) Maintenance messages or CFDS fault messages given on the PFR.

  • Compare the ECAM warning or ECAM STS message with the CFDS fault message (if applicable) on the PFR to obtain the fault symptom and the ATA chapter reference. A time difference of 1-3 minutes between the fault message and the warning message may occur due to CFDIU internal behaviour.
  • Use the Troubleshooting function to retrieve the fault symptom using Warnings/malfunctions or the correlated CFDS messages and retrieve the associated fault isolation procedure.

Troubleshooting of Faults not Reported on PFR

The following general procedure describes troubleshooting of Inop System messages, Lower ECAM DU flags/advisories, local warnings and crew or maintenance observations.

  • Use the Troubleshooting function to retrieve the fault symptom and correlate the CFDS message (if any).
  • The fault isolation procedure is displayed after identification of the relevant fault symptom.

Troubleshooting of CFDS Fault Messages

The following general procedure describes troubleshooting of CFDS Fault Messages.

  • Note the CFDS fault message ATA chapter reference.
  • Use the troubleshooting function to retrieve the CFDS message. The fault isolation procedure is displayed when the CFDS message is identified.

Troubleshooting Tips

Fault symptoms

Fault Symptoms given in the TSM contain primary faults (identified as “Correlated with” in the Troubleshooting function) and associated faults (identified as “Possible Warnings/Malfunctions” in the Troubleshooting function).

Fault isolation procedures

A computer reset may clear an intermittent fault without correcting the cause. In some cases a computer reset may hide failure conditions (i.e. in-flight conditions no longer present on ground) that may lead to unsafe conditions on the next flight.

The system reset guidelines detailed in the TSM ATA 24 provide a reset table and the system reset restrictions to confirm intermittent faults or faults generated by electrical transients.

Fault confirmation
1. Permanent fault

The fault is confirmed on the ground by performing the test given in the fault confirmation paragraph. Consequently, the procedure must be applied to troubleshoot the A/C.

2. Intermittent fault

The fault is not confirmed on the ground by performing the test given in the fault confirmation paragraph. The CFDS for some systems may display (INTM) when an intermittent operation of the system is detected.
Example of message: NO BSCU DATA (INTM)

If the confirmation test result is “TEST OK” or equivalent, the aircraft may be dispatched providing recording in logbook and monitoring of the subject fault.

When a fault is not confirmed on ground, AIRBUS recommends using the Ground Scanning function of the related system in addition to the test required in the Fault Confirmation paragraph. The ground Scanning function is an additional means to track intermittent faults and to confirm faults on ground.

When the Fault Confirmation paragraph contains the wording “Not Applicable” (or equivalent), you must do the Fault Isolation steps.

The TSM has been designed to isolate/troubleshoot permanent faults. However depending on the airlines organization, the following can be applied for intermittent fault indications:

if the test result is “TEST OK” (fault not confirmed), dispatch the aircraft, then monitor the reported symptom on the following flights by checking:

  • the previous leg reports
  • the PFR/Previous PFRs (if available)
  • the logbook of the previous flights.

After three occurrences of the same fault indication, (even though the test is still OK), the fault isolation procedure must be applied.

Fault indications generated by Electrical Transients:

On ground, especially during power-up, engine/APU start, electrical transfer, etc, Warnings may be generated by electrical transients without the related aircraft system being actually faulty. Only in such situation if after a reset the fault indication disappears, the aircraft can be dispatched. If after a reset the fault is confirmed, apply the troubleshooting procedure, or MEL if applicable for aircraft dispatch.

Swapping for troubleshooting purpose

When a reported fault is not confirmed on the ground (all tests given in the fault confirmation paragraph are done and the results are correct), it is possible to swap identical LRUs installed on the same A/C for subsequent flights for data analysis and decrease the NFF rate.

When a fault is confirmed on the ground, it is not allowed to swap LRUs as a troubleshooting step unless the TSM tells you to do so.

One Comment

Leave a Reply

Your email address will not be published. Required fields are marked *