What condition must be met for an aircraft to be "number one" in the upwind position?

For an aircraft to be considered "number one" in the upwind position, it must meet specific Standard Operating Procedures (SOPs) for departure. Being "number one" implies that the aircraft is the first to take off in a sequence, and fulfilling SOPs is crucial as they outline the required actions and safety protocols for initiating a takeoff.

SOPs typically include factors such as communication with air traffic control (ATC), ensuring the runway is clear, and confirming all pre-takeoff checks are completed. By adhering to these procedures, the pilot ensures that the aircraft is properly prepared and legally authorized to depart. This regulatory framework helps to maintain safety and efficiency in busy airspace operations, particularly during departure sequences where multiple aircraft may be involved.

While other options mention various situations, they don't specifically address the requirement that determines when an aircraft can rightfully claim the upwind position for takeoff. Thus, referencing and following SOPs is essential for operations in controlled air space to mitigate risks and facilitate safe departures.