If you work for or operate an FBO or flight school that offers aircraft rental as well as flight instruction, whether Part 61 or 141, you know the timing for completing aircraft inspections can sometimes be confusing. Now, I'm not talking about the annual inspection that must be conducted on all aircraft every twelve calendar months or sooner pursuant to 14 C.F.R. 91.409(a). That requirement isn't particularly confusing. Rather, it is the 100-hour inspection under 14 C.F.R. 91.409(b) and its timing and limitations that are sometimes misunderstood.
Section 91.409(b) states that "no person may operate an aircraft carrying any person (other than a crewmember) for hire, and no person may give flight instruction for hire in an aircraft which that person provides, unless within the preceding 100 hours of time in service the aircraft has received an annual or 100-hour inspection." Thus, unless the aircraft is subject to a progressive inspection program, or is a large aircraft (to which 14 C.F.R. Part 125 is not applicable), turbojet multiengine aircraft, turbopropeller-powered multiengine aircraft, or turbine-powered rotorcraft which has selected an inspection program under Section 91.409(f), then that aircraft must receive an annual or 100-hour inspection if it is going to be used for flight instruction.
Keep in mind that the 100-hour limitation may be exceeded by up to 10 hours as long as that time accrues while the aircraft is enroute to reach a place where the inspection can be done. However, if that happens, the additional time used to fly to the facility performing the inspection must be included in computing the next 100 hours of time for the aircraft to be in service.
Now, in order to determine whether the 100-hour inspection is required for an aircraft that is used for both flight instruction and rental, and when that inspection is due, we need to look at how the aircraft is operated during a particular flight. And this is where some of the confusion occurs. If the flight is operated for the purposes of providing flight instruction, then the aircraft must have had an annual or 100-hour inspection within the preceding 100 hours of time in service. But if the aircraft is simply rented to a customer without a pilot or flight instructor, then the aircraft need not have had an annual or 100-hour inspection within the preceding 100 hours of time in service.
How does this apply in real-life? Here are some scenarios where the FBO or flight school uses an aircraft for both flight instruction and rental and how Section 91.409(b) may or may not apply to the example flights.
Example 1: A customer reserves an aircraft for rental only and anticipates flying approximately 10 hours. When the customer reserves the aircraft, it has a total of 95 hours of time in service since the aircraft's last annual inspection. If the customer's flight does not exceed 10 hours and a 100-hour inspection is performed upon the aircraft's return, does this violate Section 91.409(b)? No, because the aircraft is not being operated for hire or to provide flight instruction. In fact, when the customer returns the aircraft does not need an annual or 100-hour inspection unless it is going to be used for flight instruction, or 12 calendar months have elapsed since the aircraft's last annual inspection.
Example 2: The FBO or flight school dispatches an aircraft on a local training flight with a flight instructor and student pilot that is anticipated to, and does last one hour. At the time of dispatch, the aircraft has accumulated 99.9 hours of time in service since the aircraft's last inspection. A 100-hour inspection of the aircraft is performed when the aircraft returns from the flight.
Is this a violation of Section 91.409(b)? Yes, because the flight instructor and student pilot clearly intend to fly beyond the 100-hour limitation during their training flight. The 10-hour grace period does not apply because the aircraft was not being flown enroute to a location where the inspection will be performed. Rather, the aircraft was operated on a local training flight which does not benefit from the 10-hour grace period. As a result, Section 91.409(b) is violated after the first tenth of an hour during the training flight. If the FBO or flight school wants to continue to use the aircraft for flight instruction after this flight, an annual or 100-hour inspection must be performed and the next inspection after that must be performed before the next 91 hours of time in service.
Example 3: An aircraft is dispatched on a cross country training flight with a flight instructor and student pilot. The flight is anticipated to take 1.5 hours of flight time to the destination and also 1.5 hours of flight time on the return trip. When the flight departs, the aircraft has accumulated 97 hours of time in service since its last inspection. During the cross country flight, unexpected winds and ATC vectoring result in the trip taking a total of 3.1 hours flight time. Upon return, a 100-hour inspection of the aircraft is conducted.
This situation does not violate Section 91.409(b). Why? The flight instructor and student pilot did not intend to overfly the 100-hour limitation. Additionally, the 100-hour limitation was exceeded while the aircraft was enroute to a location where the required inspection will be performed (e.g. the original departure airport). When the aircraft returns, an annual or 100-hour inspection will be required before the aircraft may be used for flight instruction, and the next inspection after that must be performed before the next 99.9 hours of time in service in order to continue to use the aircraft for flight instruction.
Example 4: An FBO or flight school owns an aircraft that has accumulated 100-hours since its last inspection. Although the aircraft is used for flight instruction, an inspection cannot be performed within the next week. As a result, the aircraft's schedule is marked "for rental use only." During the next week the aircraft is rented to customers, without a flight instructor, who accumulate a total of 15 hours of flight time. Additionally, no flight instruction is performed with the aircraft during the week.
Similar to Example 1, this situation does not violate Section 91.409(b). The 100-hour inspection requirement does not apply to aircraft operated for rental purposes and the FBO or flight school is free to rent the aircraft to customers as long as it is not providing a flight instructor or pilot and the customer is not operating the aircraft for hire. However, before the aircraft is again used for flight instruction an annual or 100-hour inspection must be performed and the next inspection after that must be performed before the next 85 hours of time in service in order to continue to use the aircraft for flight instruction.
As you can see, in order to apply Section 91.409(b)'s 100-hour inspection limitation it is important to not only look at the purpose of a flight, but also the intention of the operator in conducting the flight. Further, as is the case with all areas of regulatory compliance, it is critical that you have documentation or other evidence to be able to prove the purpose and intention for the flight. Aircraft schedules and rental agreements should include the purpose of the flight (e.g. rental or flight instruction) as well as the intentions for the flight (e.g. local, cross country etc.). With an understanding of Section 91.409(b)'s limitations and documentation in hand, you will be able to prove that you properly performed your 100-hour inspections in compliance with the regulations.