Question of the month: Does TBO apply to flying clubs? (2023)

Gather two pilots and drop the phrase "TBO". Now step back and watch the fireworks!

No doubt, if you operate a plane long enough, at some point in the future it will require work on the engine and propeller. Whether it's a repair, overall, or replacement depends on a number of factors, but it will happen, and clubs need to prepare for that certainty. Although the notion of TBO is more familiar when applied to engines and propellers, there are other real or experience-based TBOs that deserve attention... we'll look at some of these later in this article.

TBO, "time between overhauls", is a simple concept that is (very) often misunderstood, which can quickly become expensive. If you think about it, the literal TBO doesn't make much sense. Why would you review something if you don't need it? In fact, given what we now know, that fiddling with anything unnecessarily will most likely result in a mess, then time alone doesn't seem like a good enough reason to fiddle with things.Bottom line... if it ain't broke, don't fix it!

Now, there's a lot more science behind this than a hackneyed idiom. In fact, in aviation terms, it goes back to WWII, when the RAF (Royal Air Force, not the other) realized that initial reliability after performing time-based maintenance was actually worse than (in general) do not perform maintenance. absolutely. I use "in general" here because common sense (and indeed more science) shows that maintenance is a good thing. The point here is that blindly tearing down a complicated machine just because "it's time" can increase the risk of a problem. In addition to the possibility that the job was not done correctly, there is a finite probability that, for example, a tool is left in the wrong place, or a cable is broken, or... If you've experienced the chaos of everything falling apart after your IT group completes scheduled computer maintenance, then you'll get the point.

On the other hand, not doing any maintenance and just letting things wear out is not going to work (literally) for aviation, and not just for the planes themselves; clearly we want to make sure that the ATC system is maintained. at a reliable level, that NOTAMs are reliably available (oh, wait...), and so on.Without going into details, this is why there is so much attention on "aging aviation infrastructure" right now... the uninformed see a failure as proof that the system is worn out, which is actually a big injustice to dedicated people keep it running and keep us safe.

Forward. I think it's fair to say that the notion of TBO is not just a ploy by the manufacturer to get people to part with money, and that it does, in fact, have a place on the preventative maintenance continuum. I will also say that in many situations it is a good thing, especially when history and statistics show that there are more benefits than risks. By the way, keep in mind that we are talking about real, invasive maintenance here and not inspections, mandatory or otherwise. Clearly yearly, rolling, 100 hour inspections, or whatever, are good things, especially when a time bomb is found, but we're talking about the risks of doing complicated maintenance, and I'd say taking an engine apart it is a complicated task!

By the way, if you are now wondering if 100 hour inspections apply to flying club aircraft,please read this article.

This is not an either-or argument.Some time-based maintenance is absolutely necessary, and we all need to do it for a few things and circumstances. Check tire pressure every week, lubricate every month, change oil and filter after n hours of use…it all makes sense. However, checking tire pressure is not likely to lead to engine failure, so we should always look at both sides of the coin and weigh the benefits of performing maintenance thatcouldlead to unintended consequences (and indeed the severity of the consequences) with the fairly certain result of no maintenance at all.

There is so much more that can be said about this, and luckily for us, a lot of it has already been said by people more qualified than myself... see the reference at the end of this article!

Ok, the stage is now set for the relevant part of this article... Does TBO apply to club planes?

Well, for starters, TBO is not required for Part 91 (flying club) aircraft, unless prescribed by an AD, but it should definitely be considered as an arrow in the club team's safety and reliability quiver. . It's just not sensible to say that "we don't have to comply with TBOs" just because it's not required under the regulations.In fact, a counter argument is that if it applies to other operations under the rules, why wouldn't we comply? After all, the aircraft doesn't care what FAR Part it is operating under!This is the same debate for the 100-hour inspection of flying club aircraft, even if the club's operations don't trigger FAR 91.409(b), and they absolutely shouldn't, if the data shows that other operations are safer because to 100 hour inspections. Why wouldn't a club make them? Some members will argue that it will increase the cost of flying, and indeed it will, but what is the price of safety?

I suggest that a better approach is to consider the non-mandatory aspect of TBO, and 100 hour inspections, as offering a consciously and carefully applied level of flexibility. If a club's aircraft flies 120 hours between (non-negotiable) annuals, then it may be reasonable for a club to exercise its right not to conduct 100-hour inspections. But what about the club plane that flies 200, 300, 400 hours annually? If the data (and derived regulations) state that aircraft operations for hire or compensation, or provided for flight training purposes, require 100-hour inspections to protect the public, why wouldn't club members want to be equally protected?

At the end of the day, for the flying clubs, the 100 hour argument probably comes down to the cost of flying, but then again, what price is safety? If a club plane flies less than 100 hours on a yearly basis, then don't worry. If a club aircraft flies, say, 120 hours between annuals, then club members should have the option (via vote) to wait for the annual, but if an aircraft regularly flies more than 100 hours (and the actual threshold should be discussed and openly agreed), then a payment plan must be established. It doesn't really add much to the cost of flying since, by definition, a 100 hour inspection pays for itself in 100 flight hours. Let's say a 100 hour inspection costs $1500. Add $15 per hour (equivalent to about 2 gallons of fuel) to the usage fee, so the money is in the bank when the plane reaches 100 hours. If for any reason you don't reach 100 hours annually, use the extra money for an improvement fund or provide a refund to members. If you still decide not to do time-based inspections between yearly, at least be more diligent about oil changes so you can keep track of trends and evolving situations.

I propose that the TBO engine and prop situation is very similar to the 100 hour case. Plan and budget based on the manufacturer's TBO, but exercise flexibility by carefully monitoring actual conditions. Let's say the recommended TBO of the engine is 2000 hours and assume there are 1000 hours left before that time is reached. For a $30,000 overhaul (or replacement or whatever), you need to save $30 an hour. If there are 1500 hours left on the motor this drops to $20 per hour and with the new motor in place the load per hour on the motor will drop to $15 so start saving as soon as you can. The same goes for the TBO prop, so add a few more bucks for that.

A quick clarification, here. It is true that club standard (airworthiness) category aircraft operating under Part 91 do not “need” to meet TBO recommendations, unless required by an FAA-issued AD. If you operate an LSA, you'll need to be a bit more careful, as by consensus airworthiness standards, manufacturer's service bulletins have the same weight and compliance requirements as ADs.


The big remaining question regarding TBO revolves around liability. I get several calls a month from club officials asking me about the risk of exceeding the recommended TBO – could the club be held liable if something bad happens and the cause is traceable to failure to follow a recommended TBO?

The hackneyed answer is “yes, there is always the possibility of liability since we fly planes”, but there is more to it than that. A better, but equally unsatisfactory answer is "maybe," but that begs the real question: "What can we do to limit our liability if we choose to go beyond the manufacturers recommended TBO?

I am not going to offer any legal advice here; for that, talk to our AOPA attorneys (you are a member of theAOPA Legal Services Plan, you do not? ), but a lot of this comes down to common sense. Exercising the privilege (under Part 91 as explained above) does not relieve you of the obligation to keep your aircraft airworthy. If your A&P/IA determines that your engine beyond TBO (or even before TBO, for that matter) is not airworthy, then you will have decisions to make. On the other hand, if the engine is deemed airworthy, I suggest there are still some sensible safety measures you can take to limit potential liability exposure; indeed, perhaps to quash any suggestion that the club is somehow negligent in not adhering to the rules. TBO, and that's going above and beyond with preventative maintenance and record keeping.

Here are some suggested actions:

  • Increase the frequency of oil changes, and of course, change the filter every time.
    • Yes, this is to keep the oil nice and clean, but it's also an opportunity to...
  • Cut the old oil filter at each change
    • Keep dated and annotated photos of the filter element open, both sides
    • Identify and catalog any particles found in the folds of the element.
    • You will likely find some carbon, but if you find "metal", follow the engine manufacturer's recommendations, to the letter.
  • When you drain the oil, take a sample and send it to your favorite analysis lab (read instructionsbeforestarting to drain the oil!)
    • Don't jump between different labs. The point is to keep a growing record of trends, rather than just spot checks.
    • Read analysis reports carefully and keep them with your maintenance records
    • If you have power, enter the data into a spreadsheet and draw some graphs, as it's easier to see emerging trends in a picture.
  • Remove and check for particles in the oil filter. This is a thick trap to keep the nasties out of the oil system on wet sump engines; read the engine operator's manual for details. The screen is usually the first line of defense, while a full flow filter is the second. Oil screens vary in location with different engines, even from the same manufacturer. Your engine's Illustrated Parts Manual is a good source for finding out where it is—it could be on the side of the crankcase or maybe on the bottom. On my Bat's O-235-L2C, the screen is on the bottom and is held in place with a 1” nut and lock washer. tools and a stock of lock washers before jumping in. You probably won't find a proper torque setting for the new nut/washer combination, but conventional wisdom says to hand-tighten until the washer is flush with the crankcase, then add an additional three-quarters of a turn to squash the washer down enough to to form a good seal. Then put a safety cable on the nut in place.
  • Depending on the oil change interval, either every change or every other, remove the (top) spark plugs and take compression readings, but perhaps more helpful and important, use a borescope and take photos (or video) of all the valves and upper cylinder. (head) as well as the condition of the cylinder walls
  • Keep impeccable records. Keep a folder with:
    • tachometer and hobbs times
    • Dated photos of the oil filter element and borescope results
    • It's not a bad idea to take pictures of the electrode ends of all the spark plugs as they come out of the heads. This can be helpful in determining emerging problems with piston rings, valve guides, etc. It's also a good way to visualize how the members tilt the engine, or not. For more information on tilt, seehereyhere.
    • Oil analysis results... read and understand. Again, graphing the results will help visualize emerging trends.
    • Oil added between changes and keep a current record of oil consumption (per hour)
    • Any other notes and observations
    • By the way, remember that most club management tools (such asflight circle) allow you to set reminders/notifications for upcoming tasks, such as oil changes.

Other TBO for Flying Clubs:

TBO is a concept that doesn't just apply to engines and propellers. Virtually every part on every machine will have a useful life and that's why we do time-based inspections. In fact, some modern composite airframes have time constraints, beyond which "intensive" maintenance is required.

Now, while I'm a big fan of condition based maintenance, there are two parts I regularly change/check on a 500 hour schedule, and those are the vacuum pump (yes...I know) and the magnetos. These parts are too important to leave to chance, and there isn't much you can see, externally, to help determine the condition. I just add the cost of these, divided by 500, into the hourly cost of my plane, so the money is there when I need it.

Carefully read your aircraft's operator's manual for maintenance schedules: what the manufacturer recommends doing every 50 hours, 100 hours, etc. Each aircraft is unique, so listen to it and learn its quirks beyond "just" recommendations. For example, I found that the vibration damper on my Aerobat needs to be serviced every 55 hours to prevent sudden onset of shaking...all seals and such are in good shape, that's just what this unit does!

Beyond the generally accepted understanding of TBO, why not expand the notion a bit further to include all other time-based club tasks? These could include:

  • Planning and annual budget
  • Update member information: things like flight hours, sure, but also a skills and talents spreadsheet to make it easy to find members to help with various tasks and projects.
  • Regular review of bylaws and operating rules - they become outdated and outdated surprisingly quickly
  • Membership on various committees to ensure good representation of members


For clubs operating under Part 91, there is no obligation or requirement to adhere to manufacturers' recommended time between overhauls unless accompanied by an FAA-issued AD or manufacturer-issued SB if the aircraft is certified. like LSAs. However, unless you truly believe that TBO is just a ploy to get you to spend more money, you would be wise to consider that it is based on data derived from thousands of hours of operation, thus setting a statistical window. Instead of just starting the engine at exactly TBO, think of it as an alarm call to get your attention.As your engine or whatever approaches the listed TBO, start taking extra precautions and increasing inspections and preventative maintenance as, at least statistically, things will start to degrade. Getting ahead of the curve will allow you to establish "normal" behavior, making it easier to spot the inevitable decline.

As you go through the planning process, think about other aspects of flying clubs that have some sense of time sensitivity and include them in your planning and reporting system. You'll be glad you did!

view this monthOutstanding clubyresource highlightfor other ideas for taking your engines beyond TBO.

As always, fly a lot and safely!


Here are some good resources to check out:

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