This is correct. To enter Class Bravo airspace, one must have clearance from Air Traffic Control. Pilots are free to request clearance through Class Bravo, bu

This is correct. To enter Class Bravo airspace, one must have clearance from Air Traffic Control. Pilots are free to request clearance through Class Bravo, but it's not always granted. For example, flying a Cessna 172 out of San Carlos Airport in the San Francisco Bay Area, it's very convenient to travel through the nearby Bravo airspace of San Francisco airport. Sometimes it's granted, other times we have to go around. Furthermore, having obtained a Bravo clearance, you must pay close attention to and promptly obey any instructions from ATC (which can be of the form "turn left 10 degrees immediately for traffic avoidance"). By contrast, controllers have no means to track drones or communicate with their pilots.