What can be a consequence of failing to properly prepare surfaces before repairs?

Failing to properly prepare surfaces before repairs can lead to weaker bonding of repair materials. Surface preparation is a critical step in ensuring that adhesives or any other bonding agents effectively adhere to the material. Poorly prepared surfaces may have contaminants like dirt, oil, corrosion, or even paint that can prevent proper adhesion. This lack of a strong bond could result in the repair failing under stress, compromising the structural integrity of the aircraft component.

In contrast to this, increased fuel efficiency, enhanced visual appeal, and longer lifespan of repaired structures are outcomes that typically relate to properly executed repairs, not the failure to prepare surfaces adequately. Therefore, the strongest reason for ensuring proper surface preparation is to achieve optimal bonding and maintain the strength and reliability of the repair.