To which types of aircraft do Airworthiness Directives (AD's) apply?

Airworthiness Directives (ADs) apply specifically to particular types of aircraft deemed to require compliance to ensure continued safety. The correct response highlights that ADs are primarily intended for standard category aircraft, which are those aircraft that are designed and manufactured under the guidelines and standards provided by aviation regulatory authorities.

Standard category aircraft include those that are certified by the FAA and meet specific design and operational standards. By issuing an AD, the FAA mandates that the owner or operator of the aircraft must comply with certain requirements, such as inspections, modifications, or other safety measures, based on findings related to the airworthiness of those aircraft.

While Airworthiness Directives can be issued for other categories, such as Light-Sport Aircraft (S-LSA) and amateur-built aircraft, they do not apply universally to all aircraft, which confirms the focus on standard category aircraft in terms of mandatory compliance through ADs. Therefore, the specificity of the answer emphasizes the regulatory approach to maintain safety standards in the more conventional and widely operated aircraft as defined by the standard category classification.