Which action is forbidden until required crewmember verification is complete?

The action that is forbidden until required crewmember verification is complete is the closing of all entry doors for taxi or pushback. This procedure is critical for ensuring that all crewmembers are present and accounted for before the aircraft begins its movement on the ground. Verification typically involves confirming that all required personnel, such as pilots and flight attendants, are on board and ready for the flight.

Safety protocols dictate that aircraft doors should remain open during the initial stages of boarding and preparation, which allows for easy access in case of an emergency or if additional personnel need to board or disembark. Once verification is complete and all necessary crewmembers are confirmed to be present, it is safe to close the entry doors, which signifies that the aircraft is ready to proceed to the next phase of its operation, such as taxiing or pushback.

The other options involve actions that can be completed without the need for prior verification of crewmember presence or readiness. For example, closing aircraft windows and releasing luggage for offloading can occur independently of crewmember verification, as these tasks do not directly affect the operational safety concerning the crew's readiness. Similarly, boarded passengers can be handled prior to full crew verification as well, provided that the aircraft is safely secured