When does a red unlocked indicator illuminate?

The red unlocked indicator illuminates when the landing gear is in transit. This indicator serves a critical purpose in informing the pilot about the status of the landing gear during the deployment or retraction process. When the landing gear is moving between the 'up' and 'down' positions, it indicates that the mechanism is not yet fully engaged, thus requiring the pilot's attention to ensure that the gear has completed its cycle.

If the landing gear was not in transit, such as when the main gear doors are closed or the landing gear is fully down and locked, the red unlocked indicator would not be illuminated. The emergency brake being applied is unrelated to the status of the landing gear and therefore would not trigger this specific indicator. Thus, the red unlocked indicator is a key safety feature that alerts pilots about the current movement of the landing gear, emphasizing the importance of ensuring that it is either fully extended or retracted before proceeding with flight operations.