Which is safer- a twin piston or a single turbine?

[astanley]

Andrew:

I've been looking into this and getting pretty frustrated in the process! The TBM is here now, but a new one is a bit more than what you may think. If you want to compare used to new, that's not apples to apples, but is valid in that you can get something now vs in the future.

It all comes back to mission and cost. Most folks don't understand the capability differences and cost differential. Part of the reason is the manufacturer still hasn't released the POH on the Eclipse; TBM has it on their site. TBM is proven; Eclipse isn't.

The Eclipse offers the redundancy and dependability of two jet engines. As dependable as TBMS may be, many people still want two fans and will pay for that. TBM is French; parts, availability, price changes due to foreign currency translation all comes into play. Eclipse is US. Eclipse seems to be efficient at FL350; the TBM would be more efficient lower. TBM is a bit slower, but has better range. Avionics are different. TBM would do shorter runways easier.

Lots of things to look at. The VLJs sound great, but still don't have much on the ramp other than Mustang (which says it's not a VLJ). If one wants proven performance; VLJs are still a pipe dream. A new plane will most likely depreciate in value quite a bit in the first couple years; the used counterpart may be more stable in price.

I'm watching because I could be in a position to play with a partner, but I'm pretty cautious. Wouldn't want to spend that much and not be happy. In my mind, what's out there isn't proven enough for me to risk that much money; I don't need to have it; it's optional. If I did want it, I don't like the pre-purchase terms I'm seeing. Some don't specify any substantial performance terms; just big picture stuff. So, I'm just not a test buyer of million dollar plus stuff.

Best,

Dave

Dave,

Thanks for the response!

I totally missed the fact that the two "biggest" (sorry Jeff) cabin-class turboprops are European - one EU, one Swiss - and parts pricing varies at inflation plus currency arbitrage. That's an excellent point.

IIRC the new TBM is in the $2.7M range, which is a lot of cake for a new plane. Assuming you twiddle with it, and by the time you have your training done and your insurance time complete, it's probably a $3M purchase. Seems like a lot of money for short capability.

Tony, to your point, I was thinking of the "summer" conundrum - building and existing storms easily passing FL250, but capping out at FL300 and FL350, which a jet can more easily get around/above if required. Now, there are those FL500 and FL600 monsters out there, but even still - in a TP, I'm taking it "on the nose", playing "find the gap" with the radar, or a significant deviation around the weather. Maybe I need to research again, but I was under the impression the TBM et al have a service ceiling in the FL280 range.

In my mind it has to come down to the mission requirements. If you need short fields, endurance, and true cabin class comfort - then you'd trade off the weather avoidance inherent in a higher-flying jet. If you want speed, two fan reliability, and less capital out (although more cost to maintain), with latest-gen technology, then you'd go VLJ.

At the end of the day, it's frustrating as heck (a guy who isn't in the market, but just thinks of these things). If I have $3M to spend on my a/c, do I want to be slogging along in the lower FL's?

Cheers,

-Andrew

 

[gismo]

Well, if you couch it in terms of catastrophic engine failure alone, you're probably right. I was looking at it in terms of sudden lack of propulsion for whatever reason, which is really the bottom line.

Yep, the perspective certainly changes the view. My thinking is that any boneheadedness precipitated failures are pretty much unrelated to the type of propulsion and therefore wouldn't affect such a choice.

 

[gismo]

I can think of two:

• The difference in the price of admission.
• The cost & time to get a type certification for turbfan aircraft.

A third is the likelihood that ATC will relagate the slower VLJs to altitudes where their fuel efficiency takes a big hit, robbing them or range as well as making the trips more expensive and slower.

 

[jdwatson]

A third is the likelihood that ATC will relagate the slower VLJs to altitudes where their fuel efficiency takes a big hit, robbing them or range as well as making the trips more expensive and slower.

Good point. That's has to be a concern of the future of VLJs. I wonder if the class of VLJs will be able to participate in RVSM.

 

[gismo]

First of all, when using Nall reports or any stats, you really have to scan at least 10 years in order to draw any conclusions. The data fluctuates wildly year to year because the sample sizes are small. I mean, 4 accidents? One guy opts not to fly and your group of victims drops by 25%.

Be that as it may, that added complexity is the whole issue. Go back to those 31 and see how many were Vmc rollovers and how many were due to lack of SE proficiency. THAT is your added risk.

An additional "added risk" albeit one that's relatively easy to manage is the temptation to minimize the importance of good maintenance in a twin "because you've got a spare engine". History shows this to be a very bad idea.

 

[gismo]

Good point. That's has to be a concern of the future of VLJs. I wonder if the class of VLJs will be able to participate in RVSM.

I'm certain that any that are certified for the higher flight levels will have to be, but I suspect that if a class of planes is known to ATC as being 100+ KTAS slower than the majority of the high fliers, they won't be allowed in the sandbox because it's too much hassle keeping them separated.

 

[astanley]

I'm certain that any that are certified for the higher flight levels will have to be, but I suspect that if a class of planes is known to ATC as being 100+ KTAS slower than the majority of the high fliers, they won't be allowed in the sandbox because it's too much hassle keeping them separated.

Great point Lance. I wonder, though, will the collective clout of such owners (and migration to "free flight", which Air Taxi/VLJ is such a huge part of) change this?

Cheers,

-Andrew

 

[Dave Siciliano]

It's very difficult to get apples to apples comparisons and to some degree, one may be comparing an existing, proven plane to a new proposed plan with no real evidence of performance, handling, quality of construction, etc. There are a lot of things to take into consideration besides payload, range at optimum altitude and conditions, etc. Several folks I've talked to have been very disappointed in Eclipse for several reasons. None of which were really addressed in the pre-purchase contract. Payload with full full seems to be about 600 pounds. When flying it out from it's home to Florida with three folks aboard, only light baggage was within parameters. Avionics are still an issue; several ADs already; required future inspections and replacements. There are quality and service issues that are unresolved.

People think if one can afford an Eclipse, many other planes are affordable that may not be. By the time one could get an Eclipse if committed today, it would be 1.8 to 2.0 Million. The two big single engine turbos are a million more than that. The Eclipse seems to be aimed more at shorter commercial operations. To carry four and some stuff, full fuel wouldn't be an option. No potty would keep commercial legs to 2 to 2.5 hours. The TBM would be more comparable than Pilatus (which has a wider cabin, potty and more comfort related items).

Let's say one had a pressurized Baron now and wanted a new one. I would think that would cost in the same range of an Eclipse today if one could purchase it. Six seats, payload with full fuel and many other things are comparable except the jet engines. That's how I would look at this. It's for a P-Baron or C-340 owner that wants newer, more capable.

Best,

Dave

 

[mantakos]

I mean, 4 accidents? One guy opts not to fly and your group of victims drops by 25%.

There are only so many multi-engine accidents to look at. If we sum up the past 8 years, we get 20 fuel management multi fatals out of 298 multi fatals, or about 6%, which is pretty close to the overall GA percentage.

So overall, GA fixed-wing sees about 6% of their fatals in "running out of gas", and 5% in "engine broke". Multis are still seeing about that 6% of "running out of gas", even if we assume that they're immune to "engine broke" (which assumes perfect execution of engine-out procedures).

Another interesting stat is the percentage of fuel management accidents that result in fatalities. This is a good measure of "how good are we at gliding". If you sum up the past 5 years, you get:
single engine fixed: 36 fatals out of 400 accidents, 9% fatal
single engine retractable: 19 fatals out of 127 accidents, 14% fatal
multi: 15 fatals out of 50 accidents, 30% fatal

So it seems like multis make for worse gliders than singles. You might speculate that this is due to higher approach speeds, or you might speculate that it's due to differences in operation (e.g. an engine out in IMC is a bigger problem).
-harry

 

[MauleSkinner]

A third is the likelihood that ATC will relagate the slower VLJs to altitudes where their fuel efficiency takes a big hit, robbing them or range as well as making the trips more expensive and slower.

I don't think this is going to be as big a deal as some people make out...With over 1000 hours in a jet that's 40 knots SLOWER than an Eclipse, I very seldom was pushed down into lower altitudes, and that was before RVSM doubled the usable altitudes in that desirable range.

Fly safe!

David

 

[Dave Siciliano]

David:

It seems to be fine now; a lot of controllers are thinking it may change in busy corridors like the NE as more traffic is added. There are a few folks flying Lears now reporting they are not being allowed to climb to their requested altitude in the NE; one guy just reported he was kept at FL280 which is not cool at all in the 30 series Lear.

Guy flying a C II was amazed he was allowed up to the mid 30s being over 100 knots slower than the airlines. He also believes it won't last. Just some opinions now, but a factor to consider.

Best,

Dave

 

[gismo]

I don't think this is going to be as big a deal as some people make out...With over 1000 hours in a jet that's 40 knots SLOWER than an Eclipse, I very seldom was pushed down into lower altitudes, and that was before RVSM doubled the usable altitudes in that desirable range.

Fly safe!

David

It does seem plausible that ATC might reserve some higher altitudes for the "slow movers" that want to fly that high. And if the FAA ever gets caught up with the 21st century, computers could handle the mix a lot better than human controllers.

 

[Witmo]

I just did a quick, highly unscientific, statistically insignificant search through the NTSB databases using engine out for searches for a twin and single engine aircraft. For the singles 12 out of the 40 accidents examined were fatal. For the twins it was 23 out of 30. This may suggest that twins are indeed less, not more safe than piston or turbine singles.

Unfortunately the statistics don't tell you how many engine failures in a twin aren't reported as accidents because the flight terminated successfully at an airport. Similarly, a single engine airplane might successfully glide to an airfield and land with no report to the NTSB but it stands to reason many more single engine aircraft don't make it to an airfield than do once the fan stops turning.

 

[Larryo]

Ah, what an open ended question

I am debating between a turbine bonanza A36 or a 58 baron. Safety is paramount, especially after experiencing piston failures in the past. I do not like the extra fuel burn associated with the baron, nor the extra cost of maintaining two engines.

Acquisition costs are about the same, insurance is higher on the baron, and speed goes to the bonanza by about 30 knots.

Any thoughts? I have spoken to old timers who swear by the "extra" engine in the baron.

The turbine Bonanza will probably cost a lot more to buy and operate, and it's not 30k faster. Some of the conversions had a non derated engine and loose power at altitude and aren't as fast as a TN Bonanza. However, takeoff performance and climb are outstanding, cruise and range are not. But you can back into your parking space.

As for safety, overall, the turbing Bo wins, but with good training, the Baron isn't far behind. The Bo is simple, easy to fly, reliable engine.

As for using the turbine to overfly weather, WAY overrated, but does have some merit. But if can get one in more trouble that just staying low. I know, Dave will argue this one.

 

[Henning]

If/When you run a piece of crap thru that turbine, your maintenance bill will off set any other advantage.

Or when you try to start it with a low battery...

 

[bbchien]

I don't think either wins. It's the pilot that makes the difference. The weak spot of the turbine Bo is going to be the propellor. It's only the turbine if you are a maroon. Four hot starts and you're out for hot section, but if you don't report/record it and keep flying there are no negative consequences for.....a while.

But, I've seen a guy do this....and he lost his turbine in the air (a compressor blade) and "laughs" about it (Allison, not a PT6). This guy is gonna get killed sooner than later....

 

[ApacheBob]

And now my two cents!



It's always been my thinking that in a twin, you are TWICE as likely to loose one than you are in a single. And in a twin with an engine out, unless you do some things pretty much exactly right, pretty quickly, you're better off just pulling BOTH throttles to idle. The light twins we are likely to fly have marginal single engine performance at best.

Just an opinion. Given the choice provided, I'd also go with the turbine single.

This brings up another "statistics" issue. When a twin pilot is forced to land on one engine, does it generate an NTSB report? I am pretty sure that a single engine aircraft that lands (in a field)(or crashes) after losing an engine will generate an NTSB report.
So you may be comparing apples and oranges.
ApacheBob

 

[ApacheBob]

Unfortunately the statistics don't tell you how many engine failures in a twin aren't reported as accidents because the flight terminated successfully at an airport. Similarly, a single engine airplane might successfully glide to an airfield and land with no report to the NTSB but it stands to reason many more single engine aircraft don't make it to an airfield than do once the fan stops turning.

Please disregard my last transmission...(since someone just said the same thing.)

 

[ApacheBob]

S........L..........O...........W............

I love slow. I fly at economy cruise and save a bundle on AvGas.

 

[Dave Siciliano]

I know, Dave will argue this one.

I don't know that I'll argue Larry

It's all judgment. A more capable plane allows a bad pilot to get into worse stuff and a good pilot to use more capability to avoid bad stuff. Kinna like leverage in the RE bus: leverage makes a good deal better and a bad deal worse

The more capable plane opens up windows of opportunity that can allow a mission to continue that would otherwise be scrubbed. Can't tell you how many times I've climbed above bad stuff in the TN A-36 and P-Baron to turn what otherwise would be a bumpy, challenging flight, into an on top in VMC very enjoyable experience.


Best,

Dave