For some of those bigger block engines, they didn't need an STC at all, just new ICA instructions:

https://www.ainonline.com/aviation-news ... c-pt6a-60s

"Minden, Nev.-based Maintenance On Reliable Engines (More Co.) received approval from the FAA for its instructions for continued airworthiness to extend the time between overhaul (TBO) for seven Pratt & Whitney Canada PT6A engine models."

"The new engines covered by the instructions are PT6A-60A, -60AG, -61, -65AG, -65AR, -65B and -65R."

It wouldn't surprise me if the engine list expands over time. I think your statement is misleading that there is some sort of issue with making the big block Pratts go past TBO when there's no evidence that is the case.

Indeed, Pratt has issued TBO extension guidance for the -67 engines in Beech 1900s, so even Pratt thinks the big block engines can go past TBO.


The logic here doesn't pencil out.

If you OH at 3500 hours and it is low cost, then most of your parts were reused. Those parts then fly another 3500 hours.

If you fly past TBO, you are flying the same parts. You get to fly them for less than doing a full disassembly and rebuild of the engine just to put the same parts back in.

If you go 1.5 TBO periods (you flew one HSI interval past TBO) and those parts are now worn out, then they would have been worn out had you overhauled at TBO, too. How does going through an overhaul prevent future part wear out? Indeed, in some cases, the overhaul CAUSES wear out. This is true, for example, with props where the blades get dressed down and end up under limits sooner if you overhaul them more.

Your airplane is worth less with a past TBO engine, no doubt, but do you get ALL the money back if you do an OH? I doubt it. So economically, you are still ahead. And a lower hull value translates into lower cost of capital, taxes, and insurance.

This all fits with your general advice of paying more money for things. Sometimes value and cost are not so related as one would hope.


No, that is incorrect. There are new limits and there are overhaul limits, and they are different. An overhaul doesn't bring everything back to "new".

Mike C.

I'm an A&P in the piston world. In that world when an engine is overhauled can be brought back to service limits, not new limits. When a turbine engine is overhauled are they required to bring it to new limits (standards)? Technically a piston engine can be overhauled, then flow for one hour and be out of service limits.

Vince

By the way Mike, instead of relying on an internet search and an inaccurate article from 2008, you need to call MORE and ask them if you can simply put a -6* engine on the MORE program.

Taking your advice will certainly be an expensive education.

Flying past TBO is one possible way to fly more economically.

Mike C.

I'm an A&P in the piston world. In that world when an engine is overhauled can be brought back to service limits, not new limits. When a turbine engine is overhauled are they required to bring it to new limits (standards)? Technically a piston engine can be overhauled, then flow for one hour and be out of service limits.

Vince

Their website says:

"The MORE STC’s cover 31 PT6A engine models, and the MORE Non-STC Version (ICA) cover all PT6A-60 series engine models."

http://www.morecompany.net/about-us/overview/

You should tell them their website is wrong about PT6A-6x engines.

Mike C.

Their website says:

"The MORE STC’s cover 31 PT6A engine models, and the MORE Non-STC Version (ICA) cover all PT6A-60 series engine models."

http://www.morecompany.net/about-us/overview/

You should tell them their website is wrong about PT6A-6x engines.

Mike C.

Cool, so you can fly past TBO on the PT6A-6x series safely with FAA approval.

I bet the basis for this is rooted in some TBO extension process Pratt has, like the Beech 1900 PT6A-67 relief they have. The MORE folks used that to convince the FAA that the same treatment Pratt does can be done by others.


It makes sense.

The new owner can apply for the same relief to the FSDO. Given the plane was already approved for that, it would seem odd they would deny it. This is like a custom inspection program under 91.409(f)(4) which doesn't transfer, but you can reapply it once you are the new owner.

Even in the unlikely event the FAA denies the new owner the same relief, the prior owner got a lot of value by flying past TBO and the new owner paid less for the aircraft with a runout engine. Even if the sales price was 100% discounted for the overhaul, they both are ahead. The seller because he got engine use past TBO, the buyer because he didn't pay extra sales tax on the engine overhaul value at purchase. Once the aircraft value is established in a runout condition, you can then pay less property tax on that value going forward.

BTW transfer of Textron LUMP doesn't involve the FSDO since it is a program provided by the OEM and qualifies under 91.409(f)(3). I had mine 6 days after I bought the plane.

Mike C.

Pay me now. Pay me later.

There is no free lunch in aviation.

I’m all for operating the small Pratts past TBO, I think, based on my experience doing so with the large Pratts isn’t cost effective.

Someone who is expense adverse like you will go past TBO.

Someone who is risk adverse will overhaul.

To each his own.

Taking your advice will certainly be an expensive education.

Flying past TBO is one possible way to fly more economically.

Mike C.

There are plenty of ways to pay too much for lunch.


You imply flying past TBO is riskier than not but present no evidence for that.

The parts in your overhauled engine are the same ones it had before the overhaul.

Taking the engine apart comes with risks. Maintenance is not risk free.

Turbine engines don't have the part to part wear that piston engines do, they just spin. Very little to go wrong.

The hot section is still inspected on the HSI interval.

Mike C.

There are plenty of ways to pay too much for lunch.


You imply flying past TBO is riskier than not but present no evidence for that.

The parts in your overhauled engine are the same ones it had before the overhaul.

Taking the engine apart comes with risks. Maintenance is not risk free.

Turbine engines don't have the part to part wear that piston engines do, they just spin. Very little to go wrong.

The hot section is still inspected on the HSI interval.

Mike C.

Can you be specific about what way they are hurting? What symptoms do they show? What parts need replacement that wouldn’t at 3600 hours?

Can you be specific about what way they are hurting? What symptoms do they show? What parts need replacement that wouldn’t at 3600 hours?

Almost always an issue in the hot section which gets regular inspections during an HSI.

So if an engine is making power, per the 5 point check or other metric, you are okay with going past TBO?


If your at TBO overhaul was inexpensive to save you money in the long run, which you claim is true, then most of your parts are retained and continued for another TBO period. If you don't overhaul, those parts are continued as well. What happens at OH that magically makes those parts last longer? The engine is getting HSI still, those are not skipped.


Hot section part, checked with HSI.


Hot section part, checked with HSI.

Basically your theory is that an OH adds life to parts in a way that an HSI can't. Explain how and what parts are these?

Mike C.