When should an escape slide be detached?

Detaching an escape slide is typically necessary under circumstances involving a fire, damage to the aircraft, or ditching. This is because an escape slide is designed for rapid evacuation of passengers and crew when safety is paramount. In situations where the aircraft is compromised, such as a fire or if it needs to be evacuated over water, ensuring that the slide is deployed correctly enables a swift and safe exit from the aircraft.

When considering other options, detaching the slide while the aircraft is simply on the ground does not warrant the same urgency, as the situation has not escalated to a threat level that necessitates evacuation. Likewise, detachment during emergency landings or at the instruction of ground control does not consistently align with establishing a safe evacuation protocol and could lead to unnecessary risks if done outside of critical situations.

Thus, the specific conditions outlined in the correct answer capture the essence of when it is vital to detach the escape slide to facilitate an urgent evacuation when faced with immediate danger.