If you own or operate an aircraft that is operated under 14 C.F.R. Part 91, you know that your aircraft requires maintenance in order to remain in an airworthy condition. And sometimes it isn’t exactly clear what maintenance items are and are not required. This can be especially true when your maintenance provider starts talking about “inspections” and “overhauls.” However, it is important to understand the difference between these two items and to know when they do and do not apply.
Inspection versus Overhaul
As a starting point, it is helpful to review 14 CFR Part 1, § 1.1 which tells us that “[m]aintenance means inspection, overhaul, repair, preservation, and the replacement of parts, but excludes preventive maintenance.” So, by definition we can see that “overhaul” and “inspection” are separate items and each a unique form of “maintenance.”
Inspections involve examinations or manual checks to determine the condition of an aircraft or one of its components. An inspection may include a routine visual examination up to a detailed examination involving complete disassembly or the use of X-ray, ultrasonic, eddy current, or magnetic particle equipment to determine the condition of the aircraft or component. In a typical inspection, the inspected component is not replaced unless it is actually defective.
On the other hand, an overhaul consists of disassembly, cleaning, inspection, repair, reassembly, and testing of the aircraft or the particular component. The primary purpose of an overhaul is to restore a component to a known good condition that will give a reasonable assurance of operation for a specified amount of time (the “time between overhauls” or “TBO”). So, while inspection of an individual aircraft component may be an integral part of an overhaul, that inspection is just one part of the overall overhaul.
Why Does The Difference Matter?
This distinction is important for Part 91 owners and operators because it will dictate in many instances whether the inspection or overhaul must be performed in order to maintain an aircraft’s airworthiness.
The regulations require each Part 91 operator to have an “inspection program” for that operator’s aircraft. This program may be a 100-hour, annual, manufacturer’s recommended inspection program, or one of the operator’s own design, depending on aircraft type. Inspection programs include scheduled inspection items to be performed at defined intervals to check for hidden damage and continued serviceability in order to determine the condition of the aircraft and its components (airframe, engines, propellers, rotors, appliances, survival equipment, and emergency equipment).
An inspection program’s “scheduled inspection items” are distinguishable from “unscheduled inspections” that are event-driven from a known malfunction or discrepancy. The purpose of unscheduled inspections is to determine the level of damage that has occurred to the aircraft or component so the operator may perform the necessary maintenance actions to restore the aircraft or component to an airworthy condition.
Unscheduled inspections items are not part of an inspection program. Similarly, inspections that are part of a larger maintenance process, such as inspections performed during an overhaul, are also not a part of an inspection program. For example, scheduled replacement of parts (such as filters, seals, etc.) that is a part of the overall maintenance program is not included in an inspection program. However, if an inspection destroys a component and requires replacement of the component after the inspection, it is appropriate to include that inspection item in the inspection program.
Functional checks are a form of an inspection as well, but such checks may not necessarily be part of an inspection program. Whether the functional check is included in an inspection program will depend upon why the inspection is being performed.
If the functional check is listed in the inspection program then it is a mandatory inspection. However, if the functional check is performed as part of the return to service after a specific maintenance activity, then the inspection is part of the maintenance procedure and is not part of the inspection program. On the other hand, the functional check could be part of a pilot’s pre- or post-flight procedure required by an aircraft flight manual or pilot’s operating handbook, in which case the inspection item is neither required by the inspection program or a maintenance procedure.
In contrast, overhauls are a form of maintenance, rather than an inspection. As such, overhauls are not included in an inspection program. However, an overhaul is a maintenance process that is part of a maintenance program, whether a manufacturer’s or FAA approved program. But Part 91 operators are generally not required to comply with a manufacturer’s entire maintenance program or program approved by the FAA (as opposed to Parts 121, 125 or 135 operators, for example, whose compliance is required).
So, this is why the distinction matters: If an inspection is included in the aircraft’s inspection program then it is mandatory. Overhauls, on the other hand, are not inspection program items, and as a result they are not mandatory for Part 91 operators.
Under § 91.403(a) the owner or operator of an aircraft is responsible for maintaining the aircraft in an airworthy condition. With an understanding of the distinction between “inspections” and “overhauls”, you will be in a better position to determine when each is required by the regulations so you can make informed decisions regarding the aircraft you own or operate under Part 91.
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