This article was initially published in June 2021. It was updated in November 2025 to add a description of the Configuration Cockpit tool.

More than 200 cases of incorrect aircraft technical configuration are reported each year to Airbus. In all cases, the aircraft was dispatched with a hardware or software standard that was not authorized to be installed on the aircraft. 

A risk of incorrect behavior of some aircraft systems

Incorrect aircraft technical configuration can lead to unexpected system behaviors, which could affect the safety of a flight, especially if the incorrect configuration has an effect on flight control or flight guidance computers, or causes certain system functions to become unavailable.

A risk of documentation providing inappropriate information or procedures

A mismatch in the aircraft technical configuration can also cause the aircraft documentation (e.g AMM, IPC, FCOM, QRH, MMEL) to not reflect the actual technical configuration of the aircraft. This may result in documentation that provides inappropriate information or procedures to the flight crew or the maintenance personnel.

The “As-delivered” configuration corresponds to the technical configuration of the aircraft at the time of Aircraft delivery. The As-Delivered configuration is described in the Aircraft Inspection Report (AIR). 

Operators can implement system improvements, corrections or add new functions, through modifications accomplished by Service Bulletins (SBs) during the entire service life of their aircraft. A SB modifies the aircraft configuration by adding, replacing or modifying hardware and/or software parts identified by a new Part Number (P/N). The Operator must report the embodiment of the service bulletin to Airbus, because Airbus uses this “As Reported” configuration of the aircraft to customize the content of the aircraft maintenance and operational documentation (fig.1). The “As reported” configuration is also the basis for fleet performance analysis and optimization. 

The Illustrated Parts Catalog (IPC) enables Operators to use a compatible P/N instead of the original P/N of a component if it is not available. This prevents unnecessary grounding of an aircraft in the case of a component failure.

Only P/Ns that are listed in the IPC as spares can be used to replace the installed P/N. This reinforces the need to report the embodiment of service bulletins to Airbus to ensure that the IPC provides the correct spare P/Ns.

Operators should be aware that if they use an IPC spare part, the aircraft documentation remains customized to the “As reported” configuration (fig.2).

Check with Maintenance

Ground technicians should contact their maintenance engineering department if they have any doubt about the “As Reported” configuration versus the actual aircraft technical configuration.

Line Replaceable Units (LRUs) and On Board Replaceable Module (OBRM)

To update a computer to a new standard on A300, A310, A320 family, A330, and A340 aircraft, a Line Replaceable Unit (LRU) can be replaced with an LRU at a new standard. For some computers on A320 family, A330, and A340 aircraft, the update can also be done by changing only a part of the computer hardware called On Board Replaceable Module (OBRM).

Data Loading Units (DLUs)

A more recent generation of computers known as Data Loadable Units (DLUs) are now used for the majority of computers. Operators can update DLUs by directly loading updated software onto the units, also known as the Field Loadable Software (FLS), using an interface in the cockpit or a portable data loader. Operators do not need to remove DLUs from the aircraft to perform their update. DLUs ease computer upgrades, simplify management of spare parts, and as a result, save time and cost.

Most of the computers installed on A220, A350 and A380 aircraft are DLUs. DLUs have been progressively introduced on A320 family, A330, and A340 aircraft since 2009. All currently delivered A320 family and A330 aircraft are equipped with several DLUs. Some computers on older A320 family, A330 and A340 aircraft are also being progressively replaced with newer DLUs. When installed with the relevant software standard, a DLU has the equivalent behavior of the older LRU that is not data loadable.

Maintenance technicians must check the P/N of the software installed on a DLU to identify the actual computer standard. Checking the P/N of the DLU hardware alone is no longer sufficient. The software P/N must also be checked and treated like any other aircraft component, and its configuration should be managed in the same way.

Cases of Incorrect Software Installed

Failing to check the software P/N installed on a DLU caused many of the reported cases of incorrect aircraft technical configuration. As a typical example, when a DLU fails and is replaced with a DLU that has the same hardware P/N, the P/N of the software preinstalled on the new unit may not be correct (fig.3).

(fig.3) Example of incorrect technical configuration of Elevator & Aileron Computers (ELAC) on A320 family aircraft due to non-compatible software preinstalled on the replacement computer

The LRU Identification Steps in the AMM/MP/AMP

The ground technicians must perform all of the steps in the AMM/MP/AMP tasks for computer removal and installation. This includes the LRU IDENTIFICATION steps that enable them to check that both the P/N of the hardware and the P/N of the software of a computer are correct.

The LRU identification page can be accessed via the SYSTEM REPORT / TEST page on the MCDU (A320 family, A330, A340 aircraft) or via the OMS (A220, A350 and A380 aircraft).

(fig.4) Example of an incorrect technical configuration visible on the LRU IDENTIFICATION page of an A320 family aircraft

A mix of DLU and non-DLU computers is possible on A320 family, A330, and A340 aircraft. It requires clear identification of the computers that are DLUs and a strict adherence to the interchangeability and mixability rules defined in the IPC.

DLU identification:

A placard located on the computer hardware enables ground technicians to identify any computer that is a DLU (fig. 5).

Mixability of DLU and Non-DLU Computers

For some computer standards, both a DLU and a non-DLU version are available and are two-way interchangeable units. The IPC usually enables the DLU and non-DLU versions to be interchanged provided that the software of the DLU version is also loaded with the correct software P/N.

(fig.6) Example of mixability for DLU and non-DLU ELAC computers on A320 family aircraft

Awareness & Training for Maintenance

Operators should ensure that maintenance technicians who work on A320 family, A330, and A340 aircraft are aware of the presence of DLUs on their aircraft and perform the necessary training to manage DLUs correctly.

Airbus developed a tool called "Configuration Cockpit" to further assist Operators in managing their aircraft technical configuration. This tool has been available since May 2024 for Skywise customers, and since June 2025 for non-Skywise customers, for the A320 family, A330, A340, A350, and A380 aircraft. 

The Configuration Cockpit tool brings an additional safety check in addition to the LRU IDENTIFICATION step against any configuration mismatch.

The operator transmits the following configuration data files to the Configuration Cockpit tool:

• The “As-maintained” configuration file for each aircraft, which corresponds to the aircraft configuration recorded in the operator’s Maintenance Information System (MIS) and/or,
• The “As-flying” configuration file, which corresponds to the actual configuration of the aircraft listed in the Avionics Configuration Report (ACR), generated by the maintenance or data loading system onboard the aircraft.   

The data files are transmitted either automatically for Skywise customers, or manually for non-Skywise customers.

The Configuration Cockpit tool checks and compares the “As-maintained” and “As-flying” configurations of each aircraft.  They are then compared to the “As-reported” configuration, known by Airbus, and crosschecked with the allowed parts list.

The results of these analyses are displayed in the Configuration Cockpit Interface.

(fig.7) Concept of the Configuration Cockpit tool

The Configuration Cockpit consists of three modules to enable the operators to get access to their aircraft configuration information.

The Configuration Checker module displays a configuration status for each aircraft. It highlights the number and percentage of identified configuration errors and lists the expected P/N (fig.8). A list of the wrong part numbers and the part numbers to be further analyzed can be displayed for each aircraft.

(fig.8) Home page of the Configuration Cockpit tool that displays fleet status

The configuration status displays the number of parts linked to a specific status:

• Wrong Part: The part number received from MIS or ACR does not match with the allowed part numbers provided in “As-reported” configuration and allowed parts list. Another reason is that the interchangeability condition for the part is not fulfilled. A “Wrong part” is considered a configuration mismatch.
• To be Analyzed: The configuration status of the part cannot be assessed automatically and requires manual checking by the Operator. This status applies to customized software parts or interchangeability conditions that cannot be determined automatically. 
• Match: The part number received from MIS or ACR matches the “As-reported” configuration and allowed parts list. The interchangeability condition, if any, is fulfilled.

The ACM module enables operators to download the list of all the modifications and Service Bulletins installed on each aircraft.

The Configuration Browser module displays the list of parts installed on the aircraft, derived from the MIS and ACR files, along with additional information. It also displays the list of modifications and Service Bulletins, including their respective concurrent requirements, if any.