When is a boom extension considered to be in its stowed position?

A boom extension is considered to be in its stowed position when it is pinned to the boom base section. This configuration ensures that the boom extension is secured and cannot move during transportation or when the crane is not in use. Pinning it to the base section prevents unintended movement or damage that could occur if the boom were left unsecured. This is critical for safety, as an unsecured boom extension could pose risks during transport or storage.

The other options depict configurations that are not suitable for stowing a boom extension. Fully extending it for transportation is contrary to the stowed position, as it indicates that the extension is being deployed rather than secured. Angling it upwards for storage does not provide the secure and stable condition required in a stowed state. Lastly, retracting to a vertical position may suggest it is prepared for use, but without being pinned, it does not meet the criteria for being considered stowed. Thus, the correct answer emphasizing the safety and practicality of securing the boom extension is pinning it to the boom base section.