A change from grade-A-cotton to a synthetic covering on a fabric-covered airplane is classified as which of the following?

A change from grade-A-cotton to a synthetic covering on a fabric-covered airplane is classified as a major alteration because it involves a significant change to the aircraft's structure or aerodynamics. Major alterations are defined as modifications that might require a new type certificate or an alteration that substantially changes the weight, balance, structure, flight characteristics, or performance of the aircraft.

Switching from a natural material to a synthetic one alters the characteristics of the covering, which can affect the aircraft's overall performance and compliance with safety standards. This type of change often requires engineering evaluation or additional testing to ensure that the new covering meets the required specifications for safety and performance, further supporting its classification as a major alteration in the eyes of aviation regulatory standards.

Other classifications do not fit this scenario adequately. Minor repairs typically refer to small fixes that restore the original condition without major changes. Also, insignificant modification or major repair does not encapsulate changes that considerably influence the safety or performance of the aircraft. This reinforces the understanding that any major change in materials warrant careful consideration and classification, ensuring ongoing compliance and safety in aviation operations.