What defines repairable damage in aircraft structures?

Repairable damage in aircraft structures is characterized by the requirement of repair to prevent performance restrictions. This type of damage implies that while the aircraft may still be safe to operate, the structural integrity or functional capability may be compromised, leading to potential limitations during flight. Addressing such damage is crucial to maintain the aircraft's operational standards and to ensure it performs as intended under various conditions.

The other options do not accurately capture the essence of what defines repairable damage. Damage that enhances the performance of the aircraft is contrary to the concept of repairable damage, as it implies an improvement rather than a detriment. Damage that does not affect the aircraft’s safety may be serious enough to warrant repair but does not encompass the broader implication of performance impacts. Finally, minor cosmetic damage that can be ignored focuses solely on surface issues and does not reflect critical structural concerns that could arise from deeper damage requiring repair.