What stipulation is there regarding corrective lenses for pilots?

The requirement that a spare set of corrective lenses must be available for pilots is based on safety considerations and the need to ensure that a pilot can maintain proper vision during flight operations. In aviation, clear vision is essential for effectively monitoring instruments, navigating, and maintaining situational awareness.

Having a spare set ensures that if a pilot's primary pair is lost or damaged, they can continue to operate the aircraft safely without delay. This requirement aligns with aviation regulations and best practices, demonstrating an emphasis on preparedness and risk mitigation.

The other options do not support the need for a pilot to have immediate access to corrective vision aids during flight, which could compromise safety. For instance, not requiring spare lenses ignores the risk of potential damage to the primary lenses, while only requiring prescription sunglasses does not account for the need for regular corrective lenses under various lighting conditions and operational environments. Additionally, sharing corrective lenses among crew members can create significant safety risks related to prescription accuracy and fit, which are critical for safe aircraft operation.