Final answer:
Crewmembers must complete a Readiness Level Progression (RLP) in each flight mode authorized by the commander to advance to Readiness Level 1 (RL1), ensuring proficiency and safety.
Step-by-step explanation:
All crewmembers must complete a Readiness Level Progression (RLP) in each mode of flight authorized by the commander before progressing to RL1. This process ensures that crewmembers have demonstrated competence in various operational conditions and are proficient in their responsibilities during flights. The RLP typically includes training and evaluation in different phases of the mission, under different environmental conditions, and potentially with different crew configurations. Meeting these requirements is essential for maintaining a high standard of safety and operational effectiveness in flight operations.