What type of damage requires notification to the NTSB?

Substantial damage that adversely affects structural strength or flight characteristics necessitates notification to the NTSB because such damage can critically compromise the safety and integrity of the aircraft. The NTSB (National Transportation Safety Board) must be informed to ensure that a thorough investigation can be conducted. This is essential not only for the aircraft involved but also for the safety of other aircraft, as similar issues could arise if not properly addressed.

In contrast, minor interior damage impacting passenger comfort or cosmetic damage that does not affect performance are not required to be reported, as these do not pose a risk to the aircraft's operational capabilities or safety. Likewise, damage that does not result in equipment failure does not meet the threshold for mandatory notification because it doesn’t directly jeopardize the safe operation of the aircraft. Thus, the correct answer emphasizes the importance of serious structural and performance-related issues that the NTSB needs to be aware of for safety oversight and potential regulatory action.