More than 30 cases of incorrect aircraft technical configuration were reported to Airbus over the last two years. In all cases, the aircraft was dispatched with a computer 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.

Every new aircraft delivered to an Operator is equipped with the latest computer standards and full compatibility with all of its systems is ensured. This is called the “As delivered” initial certified configuration of the aircraft.

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 replaces the original component with an updated component. The new component has a new Part Number (P/N) corresponding to the new standard. 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 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.4).

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).

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. 6).

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.

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 the Configuration Checker to further assist Operators in the management of their aircraft technical configuration: this tool is available in the Allowed Part(s) menu of airnav^X since June 2021 for A320 family, A330, A340, A350, and A380 aircraft.

(fig.8) Prototype of the interface of the Configuration Checker tool in the Allowed Part(s) menu of airnav^X

Operators can upload the aircraft configuration file that contains the P/Ns installed on an aircraft into the Configuration Checker. The tool then compares the installed P/Ns with the list of allowed P/Ns per position and provides a report that highlights the configuration mismatches, if any.

The Configuration Checker tool brings an additional safety check on top of the LRU IDENTIFICATION step against any configuration mismatch.

Note that the uploaded data is not archived and the report is only visible to the Operator.