BUT THERE IS NO WAY I AM CURRENTLY AWARE OF TO LEGALLY EXCEED THE MANUFACTURE'S TBO OR CYCLE LIMITS IF YOU ARE USING THE MANUFACTURE'S MAINTENANCE SCHEDULE ON A TURBINE ENGINE.
Donv might be correct that it will be hard to find a mechanic to sign off on it, because there's a lot of confusion in this area. But it's in the wording. Overhaul is not inspection. Inspection is not overhaul. Mandatory overhauls is an SB, not an AD. You can ignore SB's as part 91. However, inspections and cycles must be followed.
Let's look at 91.409.
(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, except that, the owner or operator of a turbine-powered rotorcraft may elect to use the inspection provisions of § 91.409(a), (b), (c), or (d) in lieu of an inspection option of § 91.409(f).This is the catch-all. However, the first word is Large and large means above 12500lbs as per FAA definition. However, after reading carefully, the comma between the subsequent wording makes it clear it applies to Large
as well as all the following. Which means all twin engine turboprops in our case.
But hang on, it's not over yet...Part (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:Doesn't apply to part 91.(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 § 135.411(a)(2) of this chapter.Doesn't apply to part 91.(2) An approved aircraft inspection program approved under § 135.419 of this chapter and currently in use by a person holding an operating certificate issued under part 135 of this chapter.Doesn't apply to part 91.(3) A current inspection program recommended by the manufacturer.
Does apply.(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. However, the Administrator may require revision of this inspection program in accordance with the provisions of § 91.415.Could apply if you were willing to write your own inspection program and have it approved by FSDO. But unlikely, which leaves 3. So, it's clear that an inspection program or maintenance manual must be followed, either the manufacturers recommended one (most likely their own) or one you've made up yourself and had approved. Now, let's read 43.13 and the FAA interoperation of it:
http://www.faa.gov/documentLibrary/media/Order/8620_2A.pdfApplicability.
a. Section 43.13(a) states, in part, “Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in:
1) The current manufacturer’s maintenance manual or;
2) Instructions for Continued Airworthiness prepared by its manufacturer, or;
3) Other methods, techniques, and practices acceptable to the Administrator.”
b. The language of § 43.13(a) clearly provides a person with three permissible options when performing maintenance, alterations, or preventive maintenance on a product. Section 43.13(a) does not provide an order of precedence for these three options. Further, although § 43.13(a) does not specifically address SB’s or SL’s, an OEM may legitimately incorporate an SB or SL into one of its maintenance manuals by reference. If it does so, the data specified, and the method, technique, or practice contained therein, may be acceptable to the Administrator. However, unless any method, technique, or practice prescribed by an OEM in any of its documents is specifically mandated by a regulatory document, such as Airworthiness Directive (AD), or specific regulatory language such as that in § 43.15(b); those methods, techniques, or practices are not mandatory.As you can see,
Other methods, techniques, and practices acceptable to the Administrator, not just the maintenance manual. So that contradicts or amends 91.409. But let's read on through the interpretation:
7. TCDS. Consistent with 14 CFR, a TCDS is part of a product’s type certificate (TC). A TCDS is a summary of the product’s type design. It is used primarily by authorized persons during initial or recurrent issuance of a Standard Airworthiness Certificate. It is neither a regulation, a maintenance requirements document, or a flight manual document. As such, for aircraft holding a valid and current airworthiness certificate, a TCDS should not be used as a sole source to determine what maintenance is required or what the flight operations requirements are. Any language on a TCDS, by itself, is not regulatory and is simply not enforceable. There must be a corresponding rule to make any language on the TCDS mandatory. For example, there is a mention of “operating limitations” on most TCDS. The corresponding rule for “operating limitations” is 14 CFR § 91.9(a) which states, “Except as provided in paragraph (d) of this section, no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards, or as otherwise prescribed by the certificating authority of the country of registry.” Without § 91.9, the TCDS requirement to comply with operating limitations would not be enforceable.Aha, here we reach deeper:
Any language on a TCDS, by itself, is not regulatory and is simply not enforceable. There must be a corresponding rule to make any language on the TCDS mandatory. Which means that the MM based on the engine TCDS is simply not enforceable and only a recommendation. More clarification:
8. TCDS Notes. TCDS notes are intended primarily to provide information on the various requirements for issuing an airworthiness certificate as well as the type and location of various technical documents used to operate and maintain the product. Some OEM’s have placed mandatory language such as “shall,” “must,” and “will” on their TCDS that imply that compliance with TCDS notes is mandatory. However, in the absence of regulatory language, or an AD that makes such TCDS notes mandatory, compliance with such notes is not mandatory. It would mean that FAA regulations effectively authorize OEMs to issue “substantive rules,” i.e., it would enable an OEM to impose legal requirements on the public that differ from the 14 CFR requirements. This would be objectionable for two reasons. First, the FAA does not have the authority to delegate its rulemaking authority to an OEM. Second, “substantive rules” can be adopted only in accordance with the notice and comment procedures of the Administrative Procedures Act (APA), which does not apply to an OEM.The summary:
Some OEM’s have placed mandatory language such as “shall,” “must,” and “will” on their TCDS that imply that compliance with TCDS notes is mandatory. However, in the absence of regulatory language, or an AD that makes such TCDS notes mandatory, compliance with such notes is not mandatory.So it is clear, that in general, TBO is not enforceable for part 91, not for piston, nor for turbines. However, this info is based on the long thread about PT6's and there
could be other regulatory amendments for TPE331's that make them mandatory that I'm not aware of. For instance, if overhaul times were somehow part of the aircraft TC, or in some other way inserted in a FAR or way that make them regulatory for this particular type. I don't have access to the TCDS for the TPE331, nor have I been able to find anything that suggest that anything is mandatory, but this would need an interpretation from a FSDO or someone smarter than me.
