What FAR has the operating conditions that make a 100-hour inspection mandatory?

• A. FAR Part 43
• B. FAR Part 91
• C. FAR Part 121
• D. FAR Part 135

Answer: (B)

The thing being tested is when a 100-hour inspection becomes required based on how the aircraft is used. A 100-hour inspection is mandated for aircraft that are used for hire or used for flight instruction for hire. Those operating conditions are described in FAR Part 91. When the airplane is flown in those scenarios, it must undergo a 100-hour inspection at 100-hour intervals (with the specific inspection items listed in FAR 43 Appendix D). If the aircraft is used only for private, non-hire operations, the 100-hour requirement doesn’t apply, though other inspections (like an annual) still govern airworthiness. The other parts cited cover maintenance procedures or different operator categories, but Part 91 is the one that specifies the conditions under which the 100-hour check becomes mandatory.