How They Fit Together: Part 91 Inspection vs. Part 135 Maintenanc

The things that make the nine or less operation different than Part 91 operations and those things that are different about other Part 135 operations.


Over recent months there have been many discussions about 14 CFR Part 135.411(a)(1). This is the rule that specifically defines what constitutes the infamous (nine or less) Part 135 aircraft. What we will discuss this month is all of the things that make the nine or less operation different than Part 91 operations and those things that are different about other Part 135 operations (10 or more). I will be referring exclusively to requirements applicable to large and multi-turbine powered aircraft for the purposes of this article.

For starters there is a logical transition flow from Part 91 to Part 135 nine or less and on to Part 135 ten or more. It's almost as if God created Part 91, rested then created Part 135 nine or less, rested and then created Part 135 ten or more.

First let's take a close look at Part 91 inspection requirements.

CFR Part 91.409(e)

(e) Large airplanes (to which Part 125 is not applicable), turbojet multiengine airplanes, turbopropeller-powered multiengine airplanes, and turbine-powered rotorcraft. No person may operate a large airplane, turbojet multiengine airplane, turbopropeller-powered multiengine airplane, or turbine-powered rotorcraft unless the replacement times for life-limited parts specified in the aircraft specifications, type data sheets, or other documents approved by the Administrator are complied with and the airplane or turbine-powered rotorcraft, including the airframe, engines, propellers, rotors, appliances, survival equipment, and emergency equipment, is inspected in accordance with an inspection program selected under the provisions of paragraph (f) of this section, . . .

This language refers to the replacement of life-limited parts contained in FAA approved documents such as the aircraft specifications and TCDS's. For clarity, aircraft specifications and TCDS's have basically the same purpose. Aircraft specifications were used in the past and apply to older, less complex aircraft. In those cases, life-limited parts are actually listed in the aircraft specifications. For newer aircraft which have a TCDS, the document(s) that contain a list of life-limited parts is referenced in the notes section of the TCDS itself. The TCDS points us to these additional FAA approved documents and refers to them by name and part number as well. Regardless of how you get to the list of parts, the life-limited parts are also commonly referred to as Airworthiness Limitations.

Now, the above language states that the airplane must be inspected in accordance with an inspection program selected under paragraph (f) of the same rule. And it goes on to include reference to all of the parts of the airplane — the airframe, engines, propellers, appliances, survival equipment, and emergency equipment as needing to be included in the inspection program selected. Here is what paragraph (f) looks like.

CFR Part 91.409(f)

(f) Selection of inspection program under paragraph (e) of this section. The registered owner or operator of each airplane or turbine-powered rotorcraft described in paragraph (e) of this section must select, identify in the aircraft maintenance records, and use one of the following programs for the inspection of the aircraft:

  1. A continuous airworthiness inspection program that is part of a continuous airworthiness maintenance program currently in use by a person holding an air carrier operating certificate or an operating certificate issued under Part 121 or 135 of this chapter and operating that make and model aircraft under Part 121 of this chapter or operating that make and model under Part 135 of this chapter and maintaining it under Sec. 135.411(a)(2) of this chapter.
  2. An approved aircraft inspection program approved under Sec. 135.419 of this chapter and currently in use by a person holding an operating certificate issued under Part 135 of this chapter.
  3. A current inspection program recommended by the manufacturer.
  4. Any other inspection program established by the registered owner or operator of that airplane or turbine-powered rotorcraft and approved by the Administrator under paragraph (g) of this section.
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