geosync

Us in claims don't really mind going above TBO, because wear and tear items are no covered by insurance. For instance, if you had a propstrike which requires a IRAN inspection, it is torn down to check the crankshaft, gears, etc. If the shop looks in there and lo and behold there is corrosion and worn cam lobes, that's is not insurable damage, and unrelated to the propstrike, so the owner is on the hook for that. Now, if the owner wants to go ahead and overhaul the engine while it is down for inspection, then fine. We pay for what is necessary to inspect for the propstrike(R&R, labor) so that money can be used towards the overhaul, in fact, that would be wise if near or over TBO, since the typical IRAN cost on an 0-360 is 8-10k.

If insurance covered wear and tear, every owner would end up have a mystery "propstrike" at TBO to get the company to pay for an overhaul, and the whole concept of insurance crumbles to pieces.

In the jet world, there are maintenance service plans to set aside $$ for maintenance and overhaul. In the piston world, it's left up to the owner. Of course no owner sets aside money every flight hour for a "recommended" overhaul.

rickair7777

TBO has a clear correlation to one thing... resale value. At or above TBO, the value of the plane will be about the same as a similar plane with a fresh motor, minus the cost of an overhaul.

I would have no issue going over TBO if I new the history of the motor. Probably wouldn't buy a SE plane at TBO (since my family would fly in it).

BFMthisA10

I think all of that was fairly boilerplate. My question had more to do with hull loss that was either coincidental or as a result of power loss and the engine was beyond TBO.

BFMthisA10

Yep, I’ve seen that correlation as well.

JohnBurke

What makes you think there will be a hull loss attending a power loss, and what has TBO to do with power loss?

BFMthisA10

Not to say that it would be causal, just coincident. Hull loss mishap happens, power loss is involved (for whatever reason), engine happens to be beyond TBO. My question is then, would an adjuster find the owner negligent in maintaining an airworthy powerplant in the event of a mishap, causality or not. But based on what you’ve taken the time to explain, I’m gathering that this isn’t an insurance “gotcha” so to speak.
Very helpful info; I’ve learned some things.

JohnBurke

That would depend on the operation and the policy, I suspect, but that's not my area. An insurance representative replied above, an indicated that TBO wouldn't be the determinate factor, but that excess wear on condition would not necessarily be covered, depending on circumstance.

The poster did note that the appropriate preparation for such expenses is to lay aside an hourly value for overhaul or replacement. A ballpark value for that, in my experience, has been a number roughly equivalent to the cost of fuel. Take what the fuel cost per hour, and set that amount aside in an account in preparation for maintenance. It will exceed engine cost, but will also account for other expenses during the time to TBO (or whatever interval is used).

It's worth noting that it's not uncommon for owner/operators to have a "top overhaul" or cylinders replaced on the way to TBO, in a piston engine. It's beyond the scope of this discussion, but it's not uncommon for a cylinder to be replaced, then have problems in the opposing cylinder on a horizontally opposed engine, or other issues, in a cylinder that appears otherwise functional. Removing cylinders on through bolts or bolts which affect opposite cylinders, or placing a strong cylinder opposite a weaker one, can lead to problems that add expenses and increase the potential for failure or other issues well before TBO.

Regular, consistent operation is important for long engine life, and there are many variables as to how operation might affect an engine. One of the most important parameters, often not given the due it deserves, is cylinder head temperature. With cylinder heads secured to cylinder barrels by an interference fit, it's easy to understand why excess cylinder head temperature, causing head expansion, can cause cylinder head separation. Those who consistently operate at higher temperatures place themselves at greater chance for failure.

Many who operate piston engines use single-point EGT, and some use only a single point CHT reference (ostensibly on the hottest cylinder, but not necessarily so). As a result, a great deal of data is missed, and on most piston engines, wide mixture and temperature variation can occur between cylinders. Add valve wear or carbon buildup, variations in induction tubes and exhaust, intake or induction leaks, imprecise fuel metering or mixing, and it's possible for an operator to think he or she is well clear of peak temperatures, yet operate some (or most) cylinders in unsafe ranges or ranges not conducive to long engine life.

Large or rapid power changes, power off descents, low power operation, frequency of operation, maintenance, and other practices can also reduce engine life, making TBO more nebulous as well. It's a general reference number, but there are far too many aspects to consider to see it as much more than a generic forecast.

Another element to consider is the single most common metric that owners reference when determining engine health: compression. It's a number with far less meaning than most think, and a highly variable one. I can perform a dozen compression tests on an engine and get different values each time. Engine temperature, number of revolutions since the last test, valve positioning, guide wear, test unit, evaluator, and other variables all change the compression tests, and there are ways to make it appear higher than it is, or to mistake a higher reading. An operator may think the engine is stronger or in better condition than it is.

I've see a number of magneto failures over the years, some quite spectacular. A slipped mag or change in timing can not only cause a failure or rough engine, but can cause damage that drastically reduces engine life; the engine may be well under TBO, but it's not uncommon for magnetos or accessories to require repair or overhaul well before (mags typically at half of TBO or less), and a faulty mag may introduce stresses or damage which occur at a later date and are unsuspected.

An aircraft which has been roughly maneuvered may have considerable stress placed on the crankshaft; this may not show up until some time later, and an airplane which is purchased with a good maintenance history and that is within TBO may have a catastrophic failure due to the way in which the aircraft was operated; this isn't something found in a logbook and isn't something normally passed on in the sales description. Rentals are wildcards; there's no way to know what the previous renter did, or how they operated the aircraft.

I've seen engines that are well past TBO which are in excellent condition, flown by private owners, some by 135 operators, that are strong and could go much longer. I've seen many others which never made TBO.

An engine that's got considerable internal wear, pitting, corrosion, etc, may be a lot more expensive to overhaul, which comes back to regular operation and oil changes, spectrometric oil analysis, etc.

The issue of a failure beyond TBO is also complicated by other legal issues that are beyond my expertise, such as the potential with passengers, etc. How will a civil suit for personal or property injuries play out if an attempt is made to connect the high-time engine to the injuries or damage? I can't say, but I suspect it would be a potential concern. Even if no passengers are on board, even if no damage is done by the aircraft, envision a situation in which a driver is distracted by the site of an airplane landing off field, departs the road, and injuries occur. It's possible that legal action might attach the forced landing to the vehicle incident; a lot of possibilities, but in each case I'm sure the engine condition and hours might be factors.

I think it would be wise to discuss engine times with insurance.

One of my duties involves Part 137 airplanes, and there we respect TBO, cycles, and all inspection intervals, service bulletins, AD's, and other aspects of engine maintenance. We don't push anything. Propellers are overhauled on calendar cycles, even though well under time limits. This is done in close concert with insurance, and for safety, and for value and condition as they approach TBO. These are turbine engines, but same concepts, and where questions arise, such as rocks drawn up into a prop arc, we've split at the c-flange and had repairs and overhaul done well inside TBO or inspection intervals, out of an abundance of caution. Those airplanes have just one engine, and none of us want it stopping until a runway is under us. We do the same with piston engines.

I was approached by the owner of a Seneca once who had engine trouble. When examining the engines, I didn't find a single cylinder that had better than 25/80 compression. He intended to wring every bit of flight time out of those engines, and was fortunate that he didn't have a mishap. His overhauls were expensive, as he attempted to fix the problem by swapping jugs and inherited numerous other problems, when the engines should have been torn down, or replaced. There's such thing as false economy, but TBO is a poor indicator of where the balance lies.

badflaps

Thanks for the explanations, I learned something today.

TiredSoul

It’s rare that people take this much time and effort to post a meaningful reply.
Thanks JB