Final answer:
The question involves air refueling procedural knowledge for college-level engineering related to aircraft operations, focusing on visual signals during radio silence when the receiver is behind the refueling aircraft.
Step-by-step explanation:
The question pertains to air refueling procedures, specifically regarding the radio silent methods for a receiver aircraft when it is in an astern position—meaning it is behind the tanker and preparing to receive fuel. During radio silence, standard visual signals or pre-agreed procedures are used instead of radio communication to coordinate actions between the tanker and receiver.
The closing and opening of the receptacle door by the receiver is one such visual signal. This action might indicate readiness to engage or disengage from the refueling boom or probe. Precise protocols are outlined in air refueling manuals and would be part of the required knowledge for pilots performing such operations.