The given answer "not available" indicates that the appliance is not available for a further call. This could be due to various reasons, such as the appliance being out of service, being occupied with another task, or being unable to proceed due to a specific reason. The information provided in the question does not specify the exact reason for the unavailability of the appliance, but it is clear that it is not able to respond to another call and is required to return to the station.