FAR Requirements for Life Limits

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zaven.torossian
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FAR Requirements for Life Limits

Dear BOB
As aircraft maintenance Technicians we all know that a rule has been issued that most of the aircraft steel parts has been life limited to maximum of 12 years , of service , after which the item should be removed from the aircraft and overhauled and NDT inspected.such as main landing gears , crankshafts, attach pins , flap carriages , etc...
My question is that , is there any FAR requirements or statement for such limitations. and on what basis the manufactures has limited the life of such components.
Thanking you in Advance

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Stacheair1
Stacheair1's picture

“As aircraft maintenance Technicians we all know that a rule has been issued that most of the aircraft steel parts has been life limited to maximum of 12 years , of service , after which the item should be removed from the aircraft and overhauled and NDT inspected. such as main landing gears , crankshafts, attach pins , flap carriages , etc...”

I have not heard of this 12-year maximum life limit on steel parts as being covered in the Code of Federal Regulations (CFRs) that I can find. The CFRs do not set life limits on parts, but they do refer you to the TCDS, Ads, and current manufactures manuals for life limits. The CFRs talk about record keeping and tracking as explained below, which was up dated in 1992 under section 44725 in title 49, United States Code.

Existing regulations, specifically 14 C.F.R. § 91A17(a)(2)(i), require each owner or operator to keep records containing the total time in service of the airframe, each engine, each propeller, and each rotor. This is accomplished by the owner or operator recording and tracking in some form and manner the time in service of the airframe, engines(s), propeller(s), and rotor(s) from the moment the aircraft leaves the surface of the earth until it touches it at the next point of landing, as referenced in 14 C.F.R. § 1.1. In addition, § 91.4l7(a)(2)(ii), and similar provisions in 14 C.F.R. §§ 121.380(a)(2)(iii) and 135A39(a)(2)(ii), require owners or operators (certificate holders) to keep records that show the current status of life-limited parts of each airframe, engine, propeller, rotor, and appliance.

The FAA adopted § 43.10 in response to a newly added section 44725 in title 49, United States Code, that required the agency to require the safe disposition of life-limited parts removed from an aircraft. The regulation applies directly to maintenance providers who remove and install life-limited parts. It was intended to provide the necessary information to installers of previously removed parts to ensure "they know the life remaining on a part and prevent the part being used beyond its life limit." I The records obtained from the owner or operator must be sufficient to show, with a high degree of certainty, the current status of those life-limited parts.

Section 43.10 also defines (for the purpose of that rule) life status as "the accumulated cycles, hours, or any other mandatory replacement limit of a life-limited part." These times would be derived from the requirement in § 91.417(a)(2)(ii). The FAA would expect a maintenance provider to comply with § 43.10 by having a system in place that meets the acceptable methods noted in the rule.

As we noted above, this information is found in the 1992 interpretation of section 44725. The two pertinent paragraphs from that interpretation follow:

"Under these sections, the operator needs to maintain a recordkeeping system that will substantiate the time that has accrued on the life-limited part. A complete audit trail to the origin is not needed for all life-limited parts. However, it is the responsibility of the operator to substantiate that its recordkeeping system produces sufficient and accurate data to determine how the current status was obtained. The requirement is merely to show with a sufficient degree of certainty that the time elapsed is correct. [Emphasis added.]

An audit trail tracing a life-limited part back to its origin would be required only in those situations where the operator's records are so incomplete that an accurate determination of the time elapsed on the life-limited part could not be made. We would expect a request for such records to be the exception rather than the norm." (Emphasis added.)

zaven (not verified)
Anonymous's picture

Dear Mr.Bob
I thank you for your quick reply .
Most of the manufacturers have limited the steel part of the aircraft and engines to 10 to 12 years, there after the the item should be removed from the aircraft or engine for inspection and overhaul ,even the item has not reached to its hours/ cycles limitation, such as most of the landing gears of the all airplanes ,turbine engine discs, piston engine crankshafts, variable pitch propeller hubs .
How did they reach to this limit by the manufacturer? was there any regulatory agency mandated this rule ?,
I will be very thank full if you can find an answer to this subject.

AskBob
AskBob's picture

Actually the initial answer was contributed by member Denny Pollard. Denny is well versed on the regulations from years of working on that side of the industry.

As to the question of FARs influencing OEM Life Limits there is not anything in the regulations I know of indicating what the limits should be. There are rules on OEM establishing a continued airworthiness program and rules on record-keeping on the compliance with the program but I think the actual limits are established solely by the OEM.

Now, how does the OEM come up with the limits? From contacts I have made over the years it comes down to experience and history of each model. There are some that say part sales and aged fleet retirement factor in but I would hope this is minimal.

Bob

bob.pasch
bob.pasch's picture

Zavon, in my opinion Stacheair1 is correct in that the FARs themselves do not select Life Limited items or set the times. That is left up to the manufacturers' discretion however it is cemented as a general regulation in FAR Part 23 Appendix G [G23.3(b)(1)] (... information for each part of the airplane and its engines, auxiliary power units, propellers, accessories, instruments, and equipment that provides the recommended periods at which they should be cleaned, inspected, adjusted, tested, and lubricated, and the degree of inspection, the applicable wear tolerances, and work recommended at these periods... ...The recommended overhaul periods and necessary cross reference to the Airworthiness Limitations section of the manual must also be included...) and [G23.4] (...This section must set forth each mandatory replacement time, structural inspection interval, and related structural inspection procedure required for type certification...)

Stacheair1
Stacheair1's picture

Aircraft life-limited parts are those parts identified by the aircraft manufacturer or production certificate holder as being limited to a total life counted in hours, cycles, landings, or by calendar. The question is how do manufactures set the life limits.

Life limits is set by a risk factors based on allowable damage tolerance the manufacture sets to prevent or lessen liability if the part fails.

Damage tolerance. An element of the life management process that recognizes the potential existence of component imperfections, which are the result of inherent material structure, material processing, component design, manufacturing or usage. Damage tolerance addresses this situation through the incorporation of fracture resistant design, fracture mechanics, process control, and nondestructive inspection.

The relative risk of a failure caused by material, manufacturing or service induced anomalies and the standard against which probabilistic assessment results (stated in terms of component event rates and/or engine level event rates) are compared. Since not all variables may be considered or may not be capable of being accurately quantified, the numerical predictions are used on a comparative basis to evaluate various options with the same level of inputs. Results from these analyses are typically used for design optimization to meet a predefined target, or to conduct parametric studies. This type of procedure differs from an absolute risk analysis, which attempts to consider all significant variables, and is used to quantify the predicted number of future events with safety and reliability ramifications.

FAA AC No: 33.70-1 provides guidance for manufactures on this subject, but the bottom line is product liability for the manufacture. This is why you will often see parts with a life limit to protect the manufacture because there just cannot determine how and when a part may fail based on how it is used. Thanks to all the law suits manufactures try to protect themselves and their business from being sued and put out of business.

However, in some cases based on a set of known factors, like type of metal, heat, cycles and etc. manufacture can predict very close when a part may fail. A good example is main rotor blades and certain rotating engine parts and experience or lesson learned.

No Fly Zone (not verified)
Anonymous's picture

Understanding that I am NOT an expert on (Time) life-limited parts, or any other part of airframe/power maintenance, I must believe that all of the above replies are correct. The blanket language of ten (or twelve?) years for all or most steel parts is just NOT they way the FAA makes rules! (They usually make it far more complicated...) I think it also fair to say that life-cycles for some parts, particularly on new aircraft are evolving. That's why the OEMs issue SB and the FAA often converts them into ADs. This applies to every part and adjustment on the machine, not just steel parts. The take-home here is that the ultimate responsibility for compliance with these suggestions and mandated procedures rests with the operator: One more reason to maintain direct, frequent contact with the OEM, even if there is some subscription fee involved. Compliance with ADs is mandatory and compliance with SBs and other notices that are not mandatory remains high on the list of Best Practices. Flying machines in the airways are NOT automobiles that can pull over while the operator scratches his/her head in wonder. If it fails while flying, you may fall out of the sky and go SPLAT. Follow the rules! They are there to protect you as well as others.

bob.pasch
bob.pasch's picture

While your overall assessment is very accurate Mr. Zone, SBs and ADs are NOT the methods used to set, correct or adjust Life Limited components and times affecting them. A Life-limited part, by definition, is any part for which a mandatory replacement limit is specified in the type design, the Instructions for Continued Airworthiness, or the maintenance manual, all the responsibility of the OEM.

n14ky
n14ky's picture

Bob and Dan have given you good information, to add to it here is a little more:

The Type Certificate Data Sheet will identify where to find the life limited items for a given aircraft. Aircraft TCd after about 1980 will usually have this in Chapter 4 of the Maintenance Manual if that manual is in the ATA format. Some aircraft certified before 1980 have the life limited items in the Flight Manual as that was the only FAA Approved document back then. All Life Limited items have to be FAA Approved, but the holder of the TC has to identify the component and the limit prior to certification. This all gets into a legal issue surrounding The Administrative Procedures Act and the separation of powers between the Legislative and Executive branches of government. This has to do with the way the U.S. Government is made up. If you want to know more, take an Aviation Law class.

Something to consider when discussing Life Limited items and Airworthiness Limitations. The Airworthiness Limitations identify those components required to be removed from service, or overhauled. From a Maintenance standpoint, there are also Certification Maintenance Requirements that are independent of the Airworthiness Limitations. These CMRs are usually only on Transport Category aircraft and are based on anticipated fatigue life of the aircraft. In short Airworthiness Limitations are items that need to be removed and discarded or overhauled an a set interval based on time or cycles or calendar. CMR items are inspections outside the continuous Airworthiness Inspection program. Typically service experience can be justification for adjusting your inspection program, but CMRs are fixed intervals that are not changed the same as life limited items.

As to the OPs comments about steel parts, there are far more aluminum parts that have life limits than steel. In the small airplane arena, there are still aircraft with steel fuselages, landing gear and wing hardware that are 80+ years old.

zaven (not verified)
Anonymous's picture

Dear Bob
As we all know that TCM and Textron lycoming piston engines are life limited by year with a SB and SL.which are 10 - 12 years
My question is :
1/ Are we allowed to operate those engines more then the time limit as stated in the SB or Sl.
2/ Is it mandatory to drop the engine and send to overhaul when it reaches the life limit as stated in those SB or SL .
Thank you
regards
zaven

bob.pasch
bob.pasch's picture

No sir! Respectfully, they are not LIFE LIMITED! Lycoming and TCM (and other OEMs) have set Recommended Times Between Overhaul which is quite different. If they were Life Limited, you'd have to remove and dispose of them. At TBO, the manufacturers recommend that certain maintenance actions be taken for a multitude of reasons not the least of which is liability.

They base their times on engine and component wear and tear on data they've acquired during the development and certification process and may adjust after certification based on operating information.

To answer your questions Zavon, we'd have to know how your aircraft are operated. FAR Part 91 operators are not required to comply with Recommended Times Between Overhaul as long as an authorized maintenance entity complies with the requirements of that particular aircraft's maintenance program [e.g. Annual, 100Hr for aircraft used in training, Progressive or an other program approved under §91.409(e)]. Aircraft operated under FAR Part 135 are subject to more stringent requirements under §135.411 and §135.413.

In any case, I always try to educate my customer to all aspects and options available to them regardless of how they operate. An educated customer makes informed decisions based on that knowledge and not just cost! So the more informed you are allows you to pass that knowledge to your customers.

For instance, not many people take advantage of extending TBO in Lycoming-powered flight school aircraft (or privately owned for that matter) that operates consistently for 40 hours per month may extend its TBO to 2200 or 2400 hours IAW Service Instruction 1009AW (see notes).

I've linked an article below that may help you in more depth, hope this helps...

http://www.aviationtoday.com/am/repairstations/Understanding-Piston-Engi...

Bob, is correct TBO is only an recommendation and not a life limit. That is why when you reach TBO you "should" perform 100-hour inspections on the engines and monitor them. If they were life limited it would be listed on the TCDS and they are not.

John France (not verified)
Anonymous's picture

I need to correct a statement here about Airworthiness Directives not adjusting life limits of parts. There are Airworthiness Directives that require changes to the engine life limits section (Chapter 05-10-00) of the Engine Manual and require removal of Disks at earlier life than specified in the life limits section. I know of A.D.'s on Rolls Royce Engine components that we work on.

John France
Senior Quality Engineer

AskBob
AskBob's picture

I would not want to be the IA setting is a courtroom of a wrongful death lawsuit for a over TBO engine that failed that I had signed off as airworthy.
Could alter the rest of your life.

Zaven (not verified)
Anonymous's picture

I am very thankful for the info you gave me Bob , It was so helpfull
Zaven

As and former FAA inspector I have investigated many accidents and engine failures in my career. I have been involved in some court proceeding where families want to hold a mechanic responsible. However, the FAA CRFs are law and makes the owner/operator under section 91.7 fully responsible for his or her aircraft. The mechanic is on solid legal ground performing 100-hour inspection on engines over TBO as long as the inspections meet the minimum requirements and recorded in the aircraft records. The down side is the mechanic has to defend him or herself at their own expense. For this reason, I used to carry liability insurance at a high cost.

I have learned how to protect myself and the best way is with a digital camera taking lots of pictures before and during the inspections and saving them on an external drive until the work is repeated or superseded per part 91 rules.

bob.pasch
bob.pasch's picture

Believe it or not my friend it's an every day occurrence! As a matter of business, I have done this more often than I like. The liability rests in the depth and quality of the inspection you perform. Of course, the following is predicated on the fact that the original assessment of the aircraft has been well established and is for a returning customer.

For example, I have all my customers on an oil analysis program, I recommend 35 hour oil changes and analysis for every one but those whose engines are nearing TBO I strongly request they adhere to the 35 hour oil and analysis. My reasoning for 35 hours is that you get 3 oil changes per 100 hour instead of 2 and it's more reasonable than every 25 hours; and we're all aware that analysis is based on trend data and is more critical as you approach TBO.

I educate my customers as to all their options and the possible aspects and consequences of their choices. I pay particular attention to the compression readings looking for significant differences in pressure between cylinders. I become more critical inspecting baffles, components and exhaust for signs of vibration. I like to pull valve covers and inspect springs and rockers. These are some examples of extra scrutiny and I finish with a dynamic balance.

I think we can all agree that 43 Appendix D is a joke pertaining to annual inspections. As a CRS, the manual allows us to use Appendix D however we use the manufacturer's maintenance programs for obvious reasons as well as compliance with §43.15. I peruse manufacturer's data for special inspections associated with TBO or aging. I also refer to an FAA pamphlet, Best Practices Guide for Maintaining Aging General Aviation Airplanes just to reinforce we're doing all we can.

All of this, as well as stringent quality assurance, are the reasons that I can tout a clean safety record. Since I started in aviation in 1969, NEVER has there been an incident or accident causing even a scratch on a pilot, crew member or passenger due to faulty maintenance performed by myself or my teams! NEVER! All of this won't stop the frivolous law suits from happening (remember the McDonald's hot coffee spill) but it damned sure will reinforce your ability to rebut any claim of misconduct or wrong doing...

It is interesting, but most GA owners only want the minimum performed on each inspection. I have met very few owners that would pay to have additional inspections like oil sampling or soap tests performed every 100-hour on their engines. It does cost a little extra, but in my opinion, it is well worth it to catch trends before a failure.

Families will drag many mechanics into court cases when there is a fatal accident. Their lawyers sue not only the aircraft, engine, and propeller manufactures, but also anyone that has made a part that a mechanic installed and the last A&P or IA to sign off the last 100-hour or annual inspection on the aircraft.

Most mechanics I know do not have liability insurance to cover lawsuits against them. But most lawyers know mechanic are not the deep pockets person they will get money from and will overlook them most of the time, however I have seen them go after a mechanic for personal assets like their homes.

For this reason the mechanic must know their responsibilities and limitations per FAR/CFRs and follow them. In addition, how the mechanic signs off maintenance and inspections is another liability area for mechanics. If not done correctly mechanics certainly will open themselves up for a liability claim. In the IA renewal course, I teach I cover this subject and walk through a couple of scenarios that teach the rules and how to protect yourself as a mechanic. This is an import area that I think many IA renewal course overlook this, but it is a very import area.

This area about liability would make a good discussion.

TT (not verified)
Anonymous's picture

Depends on the country. UK wise we can extend the TBO on a commecially operated aircraft, which includes schools by 20% on calenter or hours, and then subject to 100 hr inspections. a private aircraft engine can run indefinately subject to the 100 hr inspections..

see GRN24 for UK requirements

http://www.caa.co.uk/docs/33/CAP%20747%20Issue%203%202014.pdf

(page 370 to 379)

T.Rae (not verified)
Anonymous's picture

Yes, I'm sure that statement was made, as several have been made by various persons during this discussion, that were very absolute, and maybe not fully pondered. There are AD's (and many more S.B.'s) that life limit parts and even accessories. Just off the top of my head there is a Cessna late model oil pressure switch limited to 3000 Hrs. (which later was added to the Airworthiness Limitations Section of the Maint. Manual, but is still an AD), a 500 hr. paper air filter replacement, and a Twin Turbo Cessna 500 Hr. V-band clamp replacement, as well as many more, that I'm sure the very competant and well respected maker of the initial statement realizes. And I agree with almost everything else that he said, (although speaking from a person with a full 30 years experience in GA and corporate, Granted 15 years less wisdom than he has, I wish that I always had 100 % of my customers agree to do all of what I recommend, because it sounds like we recommend very similar maintenance programs for Part 91 operators, although well under 50% take my advice to spend the extra money. I'd like to just get rid of them all but it makes paying 16 mechanics harder). In short, Life limits are only Mandatory for Part 91 Operators when found in:
TC Specs
FAA Approved AFM's or POH's
AD's
Any FAA Approved Airworthiness Limitations Section ("Usually" standardized as Section 4) of:
Manufacturers Maintenance or Overhaul Manuals
Service Bulletins (but you won't find many)
Manufacturers Instructions for Continued Airworthiness
and
(Be careful here) Specified on or referenced on an FAA form 337 for a major repair or alteration done to the relevant aircraft that has been field approved. (That data is FAA approved, though let's not point this out to many FSDO Inspectors)
and there may be more that I may be forgetting or still need to learn. I try not to make Absolute statements, I'm not that good yet :)
But if there are more, they must be FAA Approved. We live under a set of rules that does not let the manufacture legislate any replacement times (impose costs) on the consumer (aircraft owner/operator) under threat of Federal prosecution ($10,000. and/or 10 Years per offense) if you do not adide by what they say. The FAA in OK City may forget that some times, but the FAA in DC does not. At least for now.
Also: Everyone go right now and voice opposition to the proposed $100. Aviation user fee in the new budget to your Senators and congressmen, It's no good for any of us. Thanks You.

T.Rae (not verified)
Anonymous's picture

I just thought of one more place that you can find life limited items that would be mandatory under Part91:
Operating Limitations either on or referenced by an other than standard or utility catagory Airworthi.ness Certificate.

Any More? I missed that one, I'm sure that I missed more. Keep thinking!

n14ky
n14ky's picture

Your comments are partially correct. Yes, an AD can place a limit on an item, but it is not an Airworthiness Limitation per se. Airworthiness Limitations are determined by the Type Certificate holder at the time of the design based on anticipated fatigue life and various other criteria. Airworthiness Directives are regulations (Part 39) and are issued as a result of finding unsafe conditions that may be present in an aviation product. Airworthiness Directivvees have to go through the regulatory process and outlined in the Administrative Procedures Act.

A manufacturer or TC holder cannot change the Airworthiness Limitations section post fact as that would violate the Administrative Procedures Act. That is why most after the fact safety issues result in an AD.

In truth, we have to abide by both ADs and Airworthiness Limitations. They both may require the retirement of certain products, or direct certain maintenance actions.

When we talk about ADs, and Airworthiness Limitations, lets not forget about Certification Maintenance Requirements. CMRs are maintenance actions that are required to be complied with based on the certification requirements for the aircraft. They usually only appear in Transport Category aircraft, and will be identified in the TCDS.

Anonymous (not verified)
Anonymous's picture

I would not want to be the IA sitting in a courtroom of a wrongful death lawsuit for a UNDER TBO engine that failed that I had signed off as airworthy. That could alter the rest of you life too.

Really, don't imagine circumstances that don't exist. There have been plenty of cases where the scenario you described has happened. As long as you performed your work in accordance with the manuals, ADs, and regulations, the TBO isn't an issue. If you are more afraid of the imagined actions of a lawyer than you are of doing proper maintenance, I sure wouldn't want to take a plane to you.

AskBob
AskBob's picture

Good feedback. Would like to here more on how you handle releasing aircraft over TBO. Any recomendations?

bob.pasch
bob.pasch's picture

As I said before, I have all my customers on an oil analysis program. I recommend 35 hour oil changes and analysis for every one but for those whose engines are nearing TBO I strongly request they adhere to the 35 hour oil and analysis. My reasoning for 35 hours is that you get 3 oil changes per 100 hour instead of 2 and it's more reasonable than every 25 hours; and we're all aware that analysis is based on trend data and is more critical as you approach TBO.

That said, my techs are trained to be more critical and less accepting when it comes to service tolerances. For example, spark plugs that are worn but meet minimum service limits would be replaced as would internal magneto components in similar minimal but serviceable condition.

Other areas would be minimum compressions in cylinders, checking the history on a particular low cylinder to see if it's historically been low or if it's a recent change. If a new reading, a boroscope inspection is performed. Valve springs and guide wear are a must on TBO [or close to] engines.

Engines with ANY signs of vibration are dynamically balanced. Some symptoms may be instrument panel shaking in particular the standby compass, cracking of engine baffles, generator/alternator failures and mounts breaking, vacuum pump and magneto failures, exhaust system cracks, spinner and spinner bulkhead cracking, repeated instrument & avionics failures, carburetor air box cracking, cowling and sheet metal cracking and cracked or broken engine mounts and worst case scenario-a cracked engine case.

As we all know, aside from the fact that Hartzell, McCauley and most reciprocating and turbine engine manufacturers recommend balancing, smoother operation means less component fatigue and longer engine/airframe life. Excess vibration will shorten the life of internal engine components, engine accessories and the items listed above. This becomes more critical as TBO approaches.

Vibrations may also manifest in the rudder pedals causing your feet to "fall asleep". In this instance, it may cause a failure of stabilator attach bearings in some Piper and Cessna models.

Some TBO engines are attached to newer, modern design aircraft but the greater majority are on older aircraft, 20 years or older. It would be wise to issue AC 120-84 Aging Aircraft Inspections and Records Reviews to your techs to keep on the floor...

GLG (not verified)
Anonymous's picture

I am process of purchasing another C414 for a Part 135 operation and have found several possible purchases, however most of the airplanes have low time engines that were installed over 12 years ago. Is there any work around to have these low time engines inspected to comply with this maintenance requirement/directive?

n14ky
n14ky's picture

While Lycoming SI 1009 does call out a recommendation to overhaul in the 12th year, it's really up to the FAA PMI for the carrier. I've seen Op Specs that has the 12 year limitation, and I've seen op specs that only identify the hours limitation. Talk to the PMI and see what he would be putting in the Op Specs, and make your decision accordingly.

n14ky
n14ky's picture

Since returning an engine that is over recommended TBO to service in a Part 91 operation is within the regulatory framework, the actual return to service statement should have no more and no less than what is required by 14 CFR 43.9 or 43.11 as appropriate. Do what you say, and say what you do!

There is no liability for performing the functions of your certificate within the bounds of the regulatory system. Should you step outside those bounds, then there is the potential for liability, and certificate action.

If you are so scared of liability that you are not willing to exercise the privileges of your certificate, then you shouldn't hold said certificate! The best insurance is to do the job correctly, and document what you did correctly.

Buddy
Buddy's picture

There is another factor that might warrant consideration relative to overhauls and “Recommended” maintenance activity and that is your insurance underwriter. I have yet to see an insurance contract that did not have a rather large section that spoke directly to what MUST be accomplished if you expect them to pay any claims. In most cases, the Insurance underwriter will make the FAA look like “Bambi”.

Earlier in this string the question was asked “How do the OEM’s establish the mandatory retirement lives?”

I had the pleasure and honor of working in one the helicopter OEM’s “Destruction Laboratory’s”. This is where they drive flight critical parts to finite life. They hired myself and one other A&P so we could assemble the test specimens (Helicopter Parts & Components) like they would be assembled in the “Field”. Possibly the most valuable education in my career.

I certainly cannot speak to every OEM but at the one I worked at it was absolute scientific, validated through rigorous testing. A Million string gages, with a diligent effort to test in extreme operating conditions, sand, cold, heat, salt laden environments, volcanic ask, you name it. Static testing, dynamic testing, and engineers of every flavor you can imagine. The retirement times have a 1.5 safety factor built in so the engineers can sleep at night, and minimize risk.

One might think the OEM’s prefer many short life retirement lives to sell parts. Not the case, as this approach drives the published Direct Operating Cost (D.O.C.’s) through the roof, and would drastically affect sales. It’s actually more prudent to impose inspections with tight wear tolerances and allow the operator to retire the part/component.

I can speak only as a former FAA inspector on this subject. There is a difference in Part 91 TBO and Part 135. Under part 91 the engines can be over TBO and have a 100-hour inspection and be on condition under part 43 Appendix D. However, for part 135 aircarrier operator the FAA OpSpec will default to what every maintenance program the aircraft is on in most cases. Usually the aircraft on a part 135 certificate will be on the manufactures maintenance program so all the Service Bulletins would apply as well as TBO and all time limit inspections as well. Many of the aircraft on Part 91 and 135 will also be on a CAMP program. Keep in mind Part 135 is held to a higher level of safety than a Part 91 aircraft. The OpSpecs will set the requirements to the maintenance program there is no way around this sorry to say. So if you are on a manufacturer’s program and it calls out a 12-year inspection for the engines it is now mandatory to accomplish this inspection to meet the airworthiness requirements on the aircraft airworthiness certificate part 1 and 2 type design and limitations.

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