What action is necessary to perform a normal descent in an airship?

To perform a normal descent in an airship, the necessary action is to valve gas, which allows for the controlled release of lifting gas, typically helium or hydrogen. When gas is released from the envelope, the overall weight of the airship increases relative to the lifting capacity, causing the airship to descend. This method allows for precise control over the descent rate, making it a safe and effective technique.

In contrast, increasing ballast, while it could also cause descent, is not the preferred method as it adds weight rather than managing the lifting gas directly. Reducing speed affects the aerodynamic forces but does not directly contribute to altitude loss in the same way that valving gas does. Engaging all stabilizers is primarily focused on maintaining or enhancing stability during flight rather than directly affecting descent rates.