Mike,
Thanks for all the useful figures. I certainly don't claim superior knowledge of the HSI or overhaul costs. But I do question the methodology of your last step, why would you overhaul a -5 (or a -10, maybe)?
I look at these aircraft as purchase price, less running costs, with a terminal value of parts when the engines are done. Maybe they are worth more... you can hang some remaining life engines on them but the likelihood of somebody overhauling -5 engines seems remote. You are more likely to upgrade to -10 engines or get whatever you can as parts. For what I hope to be my plane in the near future, I certainly am not particularly thinking it likely that I overhaul the engines in ~3000 hours. That is an infinity from today. I'm assuming terminal value of zero for what I'm looking to buy. Doesn't really matter what terminal value is, though due to the costs in between being much more significant in terms of a present value calculation. (Reminds me of the bond math on hundred year bonds, that principal payment isn't worth much, the value is in the coupon stream in NPV calcs).
The costs between today and that future date are much more interesting to me. I know more about those than I did before your post, so thanks for that.
Any idea what to expect for that gearbox inspection, I may have missed that figure.

People said that in the 1980s. I am so glad they didn't trash them back then. Seems people are perpetually predicting the end of these airplanes and they keep on trucking.

This is the golden age. There will never be another time when these classic airplanes will be built. Every one of them that goes to the junk yard is slowly eating away at the private aviation culture.

What Adam is doing is admirable. Keeping it flying doesn't make economic sense. So what. If aviation was only about making sense, very little of it would exist. So sometimes we do things for reasons that aren't related to the bottom line.


It happens. Saw a -6 on an MU2 which had been overhauled 80 hours ago. My puzzlement over that is why they didn't convert to -10 at that time, but it is what it is.


I'm guessing $15-20K if you don't need something. If they crack the gearbox and find an old torque sensor or something else ancient, could be some more. Generally, the gearboxes are fine (which is why they can go 5000+ hours without being looked at when driven by a -10 hot section).

Mike C.

Mike,
I agree with everything you said in the last post.
I think what Adam is doing is great and I hope his enthusiasm for these old birds continues to be contagious. I love his YouTube, pprune, euroga and beechtalk posts. I hope that young aviators are inspired by his experiences and the capabilities of out of production twins and decide to buy Aerostars rather than Cirri, twin Commanders rather than C172s with G1000.

Salvage value is my realistic "base case", I certainly don't look forward to it and would hope for something better. I am likely to do something sentimental rather rather than scrap a well functioning aircraft. I'd love to be wrong and discover someone else wants to buy it if I upgrade. I just think amortizing the investment to zero is a fair base case.

Also, I do appreciate your figures and I think I now understand the case for pre-TBO upgrade to -10 engines decision more than I did before. My argument is only that I think a fair analysis wouldn't include the overhaul cost, would instead be the plane or engines being sold at TBO=0 for whatever you get and would mean you amortize the purchase price, rather than reinvesting in the airframe at TBO=0.

I agree with you regarding the golden age. In terms of GA aircraft, and especially on the the multi engine front, there is nothing new or better than these old aircraft. In terms of pilots it's pretty similar, I'm in my 40s and nearly all the guys I've met who fly a lot of fixed wing, not just did their ppl and stagnated, are older than me. The exception being the young guys and girls on their way to the airlines. Maybe I'd feel a bit different if I'd bought a Cirrus, that seems to be the aircraft of choice for the crowd not worried about their medical... And I notice a decent number of young guys learning to fly helis (it is on my to do list after some great rotary experiences as a passenger and a few hours handling the t-bar of Robinsons).
[edited for numerous corrections and clarifications]

Let's hear from Bob himself:

---cut---

From: Ciholas, Mike
Sent: Thursday, November 12, 2015 11:48 PM
To: Bob Hancock
Subject: HSI, OH costs these days

Bob,

I was curious what the typical HSI are for -5, -6 engines, and -10 engines like mine?

> -5-6= 80K
> -10=45 to 90K

Also, what are typical overhaul costs for -5, -6 and -10 engines?

> -5-6=180k to 210K
> -10=160K to 215K

When I mean "typical", I mean, say, 2/3rds of the folks get out for that price or less. There are obviously the outliers who end up much more.

> Above are real numbers.

---cut---

The -10 HSI costs were higher than I expected, which I think has to do with some of them being older -10s that aren't up to SB status (engines back from the mid 90s or earlier, meaning more conversion engines are likely to be at the low end since they have upgraded torque sensors and other expensive SBs done).

The -5, -6 HSI was about what I expected, I actually said $70K, $10K less than Bob.

So, for 5400 hours on -5, -6, we got $180K for two HSI and one gearbox.

For 5000 hour eligible -10, we got $45K for one HSI and no gear box.

Add in the overhauls for a full TBO cycle, we get:

-5, -6: 5400 hours, $390K, $72/hr.
-10: 5000 hours, $260K, $52/hr.

If you consider you flew the same miles for both TBO cycles due to the extra performance of the -10, then the effective cost of the -10 is 33% less than the cost per mile of the -5, -6. For a twin, you will save about $260K over that cycle in engine work, PLUS the plane flew 400 hours less air time which saves about $100K in airframe maintenance ($250/hr?), net savings is $360K. An extra $360K will buy a -10 equipped airplane over a -5 one, and you get much of that back on sale, so the money is not lost, just tied up.

Mike C.

The -10 engine spans two generations, the first ones out in 1979, and then conversion engines starting in about 1998.

The old ones may have more expensive HSI due to lacking certain SBs.

I also now noticed I used the high end of OH for both engines.

As a historical note, the -10 engine when it first came out had serious problems to the point a -5 airplane was more valuable. The problem was carbon build up in the combustor which eroded the hot section quickly resulting in power loss after only a few hundred hours of operation. This was the "-501" engines. Later, they came out with the "-511" mod and these problems were fixed.

Mike C.

I just realized that I have never seen a Turbo Commander with 4 bladed props. I wonder why that is?

Clearance from the fuselage an issue?

Clearance from the fuselage an issue?

Let me show you one with 5-blade MT's...

Actually, I heard it was for an STC that never got finalized. But the MU-2 has the 5-blade STC, so I assume it should be possible to do for the Commander. Just need someone to put down the cash to do it. They'd look wicked with it!

Not quite as wicked as this bad boy...
Saw this over at Chino recently and I'm pretty sure this is as bad*ss as it gets outside of stuff with guns or missiles

That's pretty badass. Looks like a 400LS. Crazy performance.

Well, there's a tragic story that goes with that.

The Commander pictured suffered an in flight break up while under an experimental certificate with the 5 blade props, 4 fatalities:

http://ntsb.gov/_layouts/ntsb.aviation/ ... 004&akey=1

They were apparently going to a trade show (NBAA?) when the breakup occurred. This was the test airplane for getting the STC.

It has been 9 years since this accident, and no one has gone back to finish the job.

One thing you have to be aware of is that changing the prop blade count changes the dynamics of vibration on the airframe, particularly the tail (ask Cessna about that for the 441, a hard lesson for them, too). A question I have is whether the new prop incited vibration modes that lead to structural failure. The NTSB didn't indicate this possibility, but I would consider it something to be aware of.

The most telling thing to me is that the main wing failed in a downward direction and both elevators were separated from the horizontal tail. This is very consistent with an incited vibration mode cause failure of the tail, which then leads to downward failure of the wing. The accident reports for the 441 tail failures reads almost the same. Usually, turbulence does NOT cause downward failure of the wing, also being over gross actually improves resistance to turbulence.

So, given this particular accident and the fact no one has sought to try this again would give me pause as to putting the 5 blade on the Commanders.

Mike C.

Well, there's a tragic story that goes with that.

The Commander pictured suffered an in flight break up while under an experimental certificate with the 5 blade props, 4 fatalities:
Mike C.

Possible, but heavy rain is not the same as extreme precipitation. I also think high intensity thunderstorms are not usually 30 miles across.


Again, possible, but the majority of breakups are wings break in positive direction from a strong updraft, and/or pilot disorientation and they pull back overstressing the airplane. In both cases, that typically does NOT cause the elevators to be lost.

The signature for a tail break up occurring first is loss of tail control surfaces followed by wings failing negative G. So it seems clear the tail failed first. If the gust is strong enough to fail the tail, it usually breaks the wing first.

You can't prove it wasn't the weather, but the way the wing failed suggests the weather may not be all of it. Something let go in the tail first.

Mike C.

Here's a good document comparing the various Jetrop models from when Gulfstream owned the line. The model numbers can get confusing, so it's hard to keep track even for the initiated.

Notice that some models that came with -5's often updated to -10's, so the performance will be slightly better for the models that have had that mod done, but also more expensive to get into.