Which inspection can be substituted for a 100-hour inspection?

The correct choice is that an annual inspection can serve as a substitute for a 100-hour inspection. This is significant because both the 100-hour inspection and the annual inspection are designed to ensure that aircraft are maintained to safe operational standards, but they cater to different needs based on flight hours and time intervals.

An annual inspection is thorough and comprehensive, conducted once a year, regardless of the number of flight hours. It covers all aspects of the aircraft's airworthiness and provides a complete assessment, addressing any potential safety concerns. If an aircraft has accumulated 100 hours of operation within a year, performing an annual inspection in place of the 100-hour inspection satisfies regulatory requirements while maintaining safety and compliance.

In contrast, a progressive inspection system is a different method of aircraft maintenance intended for continuous oversight and typically does not directly correlate to the 100-hour inspection. A pre-flight inspection is vital for ensuring the aircraft is ready for immediate flight but does not replace the in-depth checks performed during a 100-hour or annual inspection. Finally, stating that no inspection can be substituted is inaccurate, as regulations explicitly allow an annual inspection to fulfill the requirements of a 100-hour inspection, thereby providing flexibility in maintenance schedules.