What capability does a DEU have in case of a failure?

The capability of a Display Electronics Unit (DEU) in the event of a failure is to control all four Multi-Function Displays (MFDs). This redundancy is crucial for ensuring that essential displays remain operational even if one or more components experience malfunctions.

In aircraft systems, the DEUs are designed to integrate and manage data from various sources, presenting it across multiple displays. If one DEU fails, the system is architected in such a way that the remaining DEUs can take over to ensure that pilots have uninterrupted access to vital flight information and controls. This design prioritizes safety and operational continuity, allowing for comprehensive situational awareness throughout the crew.

The other responses do not accurately represent the full extent of the DEU's capabilities in addressing system failures. For instance, controlling only two MFDs would limit operational capability and is not sufficient for the redundancy intended with DEUs. Reporting faulty systems may be a function of other monitoring systems but is secondary to the DEU's primary role of maintaining display functionality. Bypassing manual controls, while it might suggest an alternative in certain scenarios, does not reflect the DEU’s primary responsibility of ensuring all displays remain functional in the event of a failure.