When may a Duty Period be extended with crew concurrence?

The ability to extend a Duty Period with crew concurrence is specifically applicable when delays arise from uncontrollable circumstances. This typically refers to situations like weather disruptions, mechanical issues, or air traffic delays that are beyond the crew's control. In aviation, it is critical to ensure that crew members can operate safely and within regulatory limits, but in instances of uncontrollable delays, extending the Duty Period allows the crew to manage the situation effectively while keeping safety as the top priority. This practice acknowledges the need for flexibility in response to unexpected events while still maintaining regulatory compliance.

The other options do not accurately capture the circumstances under which a Duty Period can be extended. For instance, limitations based solely on regulatory guidelines or pre-planned circumstances do not account for real-time developments that may necessitate a change in operations, which is why recognizing uncontrollable delays is key to proper operational flexibility.