What indicates that an aircraft is ready for pushback?

An aircraft is ready for pushback primarily when it is connected to a tug or towbar, and the engines may be running to facilitate a quick departure once clearance is granted. This state indicates that the aircraft is prepared to start its taxiing process as part of the pushback maneuver. The presence of the tug or towbar indicates that ground personnel are ready to move the aircraft safely away from the gate.

In addition, when the engines are running, it typically means that the crew is preparing for an immediate taxi once the pushback is completed. The readiness for pushback in this context emphasizes operational efficiency and the aircraft's readiness to enter the next phase of its movement.

The other options don't fulfill all the criteria required to indicate readiness for pushback. For instance, if the engines are off and the beacon lights are on, this may indicate that the aircraft is stationary and not ready to move. The marshaller's position and open doors typically concern boarding or disembarkation rather than readiness for pushback. Lastly, while having wing walkers in position is essential for safety during the pushback process, it does not alone signify that the aircraft is fully prepared for the maneuver without the connection to a tug or an indication of engine readiness.