What command is important just before an aircraft is scheduled to depart?

The command "Ready to depart or ready to tow" is crucial just before an aircraft is scheduled to depart because it signifies that the aircraft and ground crew are prepared for the next phase of operations. This command ensures that all necessary pre-departure checks have been completed, and that the aircraft is in the proper position for either taxiing to the runway or moving away from the gate for towing.

By confirming readiness, the crew can ascertain that the flight will proceed without unnecessary delays and that all safety protocols are being adhered to. It creates a clear line of communication between the flight deck and ground personnel, which is vital for safe and efficient aircraft movements.

In contrast, the other commands focus on actions that follow or precede the departure phase. For instance, "Stop engines" would be used post-departure, "Deactivate airstart unit" relates to engine start procedures, and "Close external doors/retract airstair" is part of the boarding process before a flight begins. Therefore, these commands, while important at their respective stages, do not hold the same significance in confirming the immediate readiness for departure.