At a minimum, all aircraft need an annual inspection. If the aircraft is used for hire, a 100-hour inspection is needed as well. Depending on aircraft, the transponder and pitot-static system may need to be inspected as well.
The 100-hour inspection is similar to an annual inspection. The primary difference that the annual inspection must be signed off by an Airframe and Power Plant (A&P) mechanic with and Inspection Authorization (IA) designation. An annual inspection may substitute for a 100-hour inspection, but a 100-hour inspection may not substitute for an annual inspection. When used for hire, such as flight instruction, the 100-hour inspection may only be exceeded by 10 hours, and this exception is only to allow the aircraft to be transported to a maintenance facility. However, the timing of the next 100-hour inspection does not reset, it is based off the original time the 100-hour was to be completed. If a transponder is to be used in controlled airspace, it must be inspected every 24 months. If operating, instrument flight rules (IFR), the pitot-static system is inspected every 24 months as well.
Although more common in large operations, a progressive inspection program could be used. In such a program, multiple inspections are made throughout the year in order to minimize the consecutive downtime to the aircraft, allowing for less disruption to operations. For example, an inspection might be able to be completed at night or between flights, where a typical annual inspection could be a week or longer.
14 CFR 91.409 Inspections
14 CFR 91.411 Altimeter system inspection
14 CFR 91.413 Transponder test
14 CFR 43.15 Additional performance rules for inspections
14 CFR 43 Appendix D: Scope and Detail of Items To Be Included in Annual and 100-Hour Inspections
FAA-H-8083-25B Pilot’s Handbook of Aeronautical Knowledge pg. 9-8