Under what condition is it acceptable to depart when the aircraft ahead of you is in sight?

The correct answer emphasizes the importance of clearance from air traffic control when operating in controlled airspace. Clearance by the controller ensures that the proper separation and safety protocols are being adhered to. This is critical for maintaining orderly traffic flow and preventing collisions.

When the aircraft ahead of you is in sight, it indicates that you have visual contact, but it does not alone guarantee the absence of other traffic or hazards. Receiving clearance from the controller confirms that it is safe for you to depart, ensuring compliance with the established airspace management rules. Such clearance is crucial because it validates that all conditions, including spacing and traffic density, are appropriate for a safe departure.

While local Standard Operating Procedures (SOPs) and actions of the aircraft ahead provide context, they do not replace the need for clearance from air traffic control, which is the definitive authority on safety in the airspace.