Twins: why one engine has more wear than the other ?

[jdwatson]

Greetings POAers !

Most of the used twins that I've been looking at (while dreaming about affording them) have engines that have large differences in engine times. What's up with that ? Is there a particular engine that wears faster than the other ? Like the counter-rotating one ? The one that's started first ?

 

[gismo]

Greetings POAers !

Most of the used twins that I've been looking at (while dreaming about affording them) have engines that have large differences in engine times. What's up with that ? Is there a particular engine that wears faster than the other ? Like the counter-rotating one ? The one that's started first ?

If a twin is used for part 135 ops then it's common for both engines to be replaced or overhauled at the same time when both reach TBO and reaching TBO in an airworthy condition is fairly likely given the typical short calendar time it takes a twin flying charters to accumulate that much time. Otherwise engines are usually replaced/overhauled on condition which means one is likely to be need this before the other. Mine are staggered by about half the TBO which is pretty much the situation when I bought it. On the plus side, the expense of two engine replacements is spread over a longer period of time. The primary downside is that the plane is out of service a greater percentage of time since it doesn't take much longer to do two than one.

 

[rcaligan]

If a twin is used for part 135 ops then it's common for both engines to be replaced or overhauled at the same time when both reach TBO and reaching TBO in an airworthy condition is fairly likely given the typical short calendar time it takes a twin flying charters to accumulate that much time. Otherwise engines are usually replaced/overhauled on condition which means one is likely to be need this before the other. Mine are staggered by about half the TBO which is pretty much the situation when I bought it. On the plus side, the expense of two engine replacements is spread over a longer period of time. The primary downside is that the plane is out of service a greater percentage of time since it doesn't take much longer to do two than one.

What Lance said.

It's easier to plonk down $25K every five years than $50K every ten.

 

[jdwatson]

Thanks for the replies. I thought there might be a design issue or something. Odd that typically one engine or the other needs work before the other.

Twins seem to be at a bargin right now, but all that maintenance is scary.

 

[Len Lanetti]

Twins seem to be at a bargin right now, but all that maintenance is scary.

I agree. In my informal review of ad's in Trade a Plane I would say that asking prices for twins and big motor'd singles is depressed. It might be a good time to buy if your mission requires one of these aircraft.

With regard to twin engine aircraft maintenance cost...not only does it cost more to maintain and the cost is for more than just another engine 'cause there are generally more systems and those systems are generally more complicated but all of other costs are significantly increased as well... higher engine reserve, two more expensive props and prop systems, more fuel, more oil, higher insurance cost, bigger hangers cost more to rent, more training...

Len

 

[Len Lanetti]

It's easier to plonk down $25K every five years than $50K every ten.

I don't know about anyone else but I'd rather have the opportunity to invest $25,000 for an extra five years.

I've seen plenty of Part 135 and Part 91 twins with similar engine times and dissimilar engine times.

The best laid plains of mice and men are often screwed up by a line of taxiway lights. Whap! "Huh" Whap! "What the heck! "Whap! "What was that?"

Len

 

[gismo]

Odd that typically one engine or the other needs work before the other.

Not much odder than two vacuum pumps failing at different times in different airplanes operated the same way. No two engines are likely to experience the exact same life even when attached to the same airframe. Also different owners of the same airplane may react to a cylinder problem differently topping in one case and overhauling in another. Once the TSMOH gets separated, it's not likely to get back together unless an engine conversion is done.

 

[jdwatson]

Good point, thanks !

I've always wanted to fly a twin. For now, I've put the rating on hold until I can figure out how to stay current. I figure I'll have to go the partnership route, the local FBOs either don't have or don't rent twins solo. My bride fears the cost of engine replacement more than anything when it comes to "ownership".

Of course, unless I hit the powerball the point is probably moot. But a pilot can dream, no ?