When is it necessary to report a mechanical irregularity concerning battery voltage?

Reporting a mechanical irregularity concerning battery voltage is crucial when the voltage is below operational limits. This is significant because battery voltage is essential for the proper functioning of various systems on the aircraft. If the voltage drops below specified thresholds, it may indicate a malfunction that could affect the aircraft's electrical systems, potentially leading to adverse operational outcomes or safety concerns.

Monitoring battery voltage is part of ensuring the aircraft's airworthiness, and any irregularities should be addressed promptly to prevent complications during flight operations. This protocol emphasizes the importance of responding to immediate safety concerns, as it allows maintenance crews to take necessary actions before any further flights are undertaken.

The other options do not align with the critical timing of reporting voltage issues that could impact safety. For example, while reporting after landing or during pre-flight inspections is important, it is the active monitoring of operational limits that dictates immediate attention when an irregularity is detected.