REDUNDANCY

[flyinthebug]

Ya, lets pick one engine over two.

How about two ropey turbines over one good one? One turbine over two pistons? One piston over two piston?

I can only answer for me photofly...personally...Id take a decent piston twin over a single turbine anyday. Id obviously take a turbine single over a piston single. I agree that turbine technology has improved greatly, and they are very reliable engines. However, many IO540s run for 2500 hours without even blowing a single cylinder(if the pilot knows how to avoid shock cooling and treats the quadrant with gentle respect rather than a 50$ hooker).

Turbine is more reliable than piston, and i dont think anyone is arguing that. What some of us are saying is that when one engine quits and you havent got at least one more to take you to safety, your screwed. As good as turbine technology is, its not invinsible...and subject to human error (in build & quality) just like a piston engine.
So for me, 2 over 1 in almost any situation. (And im referring to a decent twin that has been maintained properly and taken care of by its skippers)

examples:
PA31-350 vs PC12...Ill take the Chieftain.
C414 vs Caravan...Ill take the C414
C337 vs C172...Ill take the 337.
DHC3 vs DHC6...Ill take the -6
You get the idea...and yes, I have time on each of these machines.
Fly safe all.

[old_man]

Only one transmission. True, but transmision failures are extremely rare. A lot less moving parts than an engine. It's much less a 'transmission' or 'gearbox' (in automotive terms) than it is a simple 90 (or whatever) degree change in drivetrain direction. Not much to it, much less to go wrong, and pretty much bullet proof.

I don't know if I would refer to it as a 'simple 90 degree change'. There is also massive reduction in speed requiring a lot of gears. It also has to feed your tail rotor as well as drive all sorts of other little things (generators, hydraulics...etc). Yes they are very reliable and have all sorts of monitoring devices to give you a heads up of an impending failure they are still a mechanical device that can fail in traditional ways (loss of oil)

I may have my facts ass backwards, but wasnt/arent transmission failures the cause of several crashes involving the RCAF sea king helicopters?

Once Seaking that ditched, http://www.airforce.forces.gc.ca/dfs-ds ... p?id=10030, not necessarily directly a transmission failure. Couldn't find others but that doesn't mean they didn't happen.

[KAG]

Every time this topic comes up I sound like a broken record - clapped out king air any day. I've had engine failures in both single and twins and I'll take the second engine Ty.

If your going to compare apples to apples compare a PC12 to the BE200 as they have similar performance. At max gross a BE200 will climb stabilized at 500'/min at 10,000' (real world test). I'll take that performance over a slightly faster long legged single any day. Don't get me wrong the PC 12 is an amazing machine, with speed and economics going for it, not to mention cabin size and that awsome cargo door.

Compare say a DC3 to a caravan, I'd actually take the van. BE100 VS C208, the 100. Sure the 100 is doggy on one engine but it will maintain flight.

Its just my opinion but a properly trained crew in clapped out twin - I would put my family in.
I would not place my family in a SEIFR anything.

[Doc]

The day twin pilots do their check rides, from take-off to landing, with one feathered, I will feel safe in a twin.

Obviously you wouldn't take off with one shut down, but I'd be happy to shut it down after take off and fly you around for pretty much anything you could want to do on a ride, with one feathered. I can do approaches, overshoots, balked landings....anything you like, within reason on one.
It's really nothing special. Training departments, and flight schools make it harder than it need be. Just relax, fly the airplane and if you're a little slow, back off the power till the speed comes back. Maintain enough airspeed for a wee buffer...that's really it. The other "trick" is go wide, and give yourself lots of time.

[The Weasel]

I may have my facts ass backwards, but wasnt/arent transmission failures the cause of several crashes involving the RCAF sea king helicopters?

Could well be. Then again, military aircraft are operated and maintained under different standards and regulations than civil aircraft.

[The Weasel]

I don't know if I would refer to it as a 'simple 90 degree change'. There is also massive reduction in speed requiring a lot of gears. It also has to feed your tail rotor as well as drive all sorts of other little things (generators, hydraulics...etc). Yes they are very reliable and have all sorts of monitoring devices to give you a heads up of an impending failure they are still a mechanical device that can fail in traditional ways (loss of oil).

Fair enough. I was over-stating the simplicity. From my experience seeing engine failures, other drive-train failures, written-off aircraft, etc, the transmission is the strongest link in the chain. Also depends on the manufacturer. Some transmissions are a little more/less bullet-proof then others.

Yes, still vulnerable to loss of oil or poor maintenance, but direct mechanical failure of a transmission is very rare.

[CID]

Doc, the problem with this thread is that you are applying redundancy against an entire category of aircraft where redundancy isn't required. Only commuter and transport category require redundant essential systems. From an ops perspective, only commercial operators need two engines to fly IFR (unless you have a factory turbine single) and contrary to what some posters stated, if you want to fly that twin IFR commercially, it MUST be capable of maintaining MSA with one engine out.

To put it in the regulator's terms, commuter and transport category airplanes must be designed so that no single failure can cause the aircraft to be incapable of continued flight and safe landing. All the rest of the categories required this risk to be "minimized".

So single engine airplanes like the PC-12 that are certified to fly SEIFR in Canada needed to demonstrate how they not only minimized the probability of NOT being able to maintain safe flight and landing due to various failures, they had to demonstrate additional mitigation for such events. You won't (for example) see any AFM procedure shutting down the engine for precautionary issues like a chip detector.

Personally, I'm not crazy about commercial SEIFR operations as a fare paying passenger in many instances but the PC-12 is an amazing aircraft with an excellent commercial safety record and the tax payers of Ontario can be comfortable in knowing that their government has selected a very competent aircraft to do the job at a much reduced cost.

And speaking of accident statistics, it's true that single engine aircraft have a better survival rate after an engine failure than a twin engine aircraft but that tends to be skewed by all the non-commercial pilots that just happened to have enough money to by a twin engine airplane they were likely not quite ready to fly.

[Doc]

Doc, the problem with this thread is that you are applying redundancy against an entire category of aircraft where redundancy isn't required. Only commuter and transport category require redundant essential systems. From an ops perspective, only commercial operators need two engines to fly IFR (unless you have a factory turbine single) and contrary to what some posters stated, if you want to fly that twin IFR commercially, it MUST be capable of maintaining MSA with one engine out.

To put it in the regulator's terms, commuter and transport category airplanes must be designed so that no single failure can cause the aircraft to be incapable of continued flight and safe landing. All the rest of the categories required this risk to be "minimized".

So single engine airplanes like the PC-12 that are certified to fly SEIFR in Canada needed to demonstrate how they not only minimized the probability of NOT being able to maintain safe flight and landing due to various failures, they had to demonstrate additional mitigation for such events. You won't (for example) see any AFM procedure shutting down the engine for precautionary issues like a chip detector.

Personally, I'm not crazy about commercial SEIFR operations as a fare paying passenger in many instances but the PC-12 is an amazing aircraft with an excellent commercial safety record and the tax payers of Ontario can be comfortable in knowing that their government has selected a very competent aircraft to do the job at a much reduced cost.

And speaking of accident statistics, it's true that single engine aircraft have a better survival rate after an engine failure than a twin engine aircraft but that tends to be skewed by all the non-commercial pilots that just happened to have enough money to by a twin engine airplane they were likely not quite ready to fly.

There are examples of redundancy beyond the number of engines.
True, a twin must be able to maintain at least MSA with an engine out. Same (in a lot of cases) engines, with the same reliability record. But a single, with the SAME engine can be allowed to become a glider? That's POLITICAL. That requirement all by itself makes the twin safer due in part, to more stringent regulations.
Basically I feel the tax payers in Ontario have been sold a bill of goods, and hood winked into "believing" they are as safe in a single as they are in a twin. And, is the reduced cost really that important? Cost means SFA to the Ontario Government. Check the money they piss into the wind EVERYWHERE ELSE. No the PC12 was a total political move....somebody knows somebody. Any other Provinces/States/Countries us single engine aircraft as their default medevac machines? I can't think of a single one?
As for the rich PPL's buying twins.......and Bonanzas etc. Very true....more in the States than Canada....but I'm sure it happens here.
This was never really intended to be a twin vs. single engine debate.....however I suspected it would become one.
Biggest problem I have with the PC12 is the way it's operated. 100 and 1/2 should NOT be legal. It should be somewhat restricted in regards to IFR limits.

[CD]

Any other Provinces/States/Countries us single engine aircraft as their default medevac machines?

Well, in the U.S., HEMS is moving more and more to single-engine helicopters... Of course, they are also having an extraordinary number of fatal accidents.

[Expat]

The day twin pilots do their check rides, from take-off to landing, with one feathered, I will feel safe in a twin.

Obviously you wouldn't take off with one shut down, but I'd be happy to shut it down after take off and fly you around for pretty much anything you could want to do on a ride, with one feathered. I can do approaches, overshoots, balked landings....anything you like, within reason on one.
It's really nothing special. Training departments, and flight schools make it harder than it need be. Just relax, fly the airplane and if you're a little slow, back off the power till the speed comes back. Maintain enough airspeed for a wee buffer...that's really it. The other "trick" is go wide, and give yourself lots of time.

Then, your my kind of guy! Take off downwind wind, on a gravel runway, up slope, at 8700 ft elevation, 35 degrees celcius, because the mountains ahead offer better SE obstacle clearance. But not much...

[Strega]

You must have never had an engine quit then....

2 is better.

For me personally, id take the "clapped out" twin over the single turbine any day.

I won't.

Perhaps over water it would be debatable. Many piston twins when flying over long stretches of water will get your feet wet should you lose an engine because of the range reduction. Light twins on ferry flights it is pretty much a given that the aircraft will be lost with an engine failure and unless you calculate your single engine fuel range requirements (does anybody do that, do the manuals even have those figures) you probably wouldn't make it on a revenue flight where fuel is at the minimum required.

Perhaps it would be closer to help and give you more time to prepare when you go in or perhaps even make a diversionary field, but the failure rate of two piston engines is several orders greater than a single turbine with an alternate fuel control. Remember, it's not just the hours but the speed--with the exception of the Caravan, a single turbine will cover more distance per hour.

Over the rocks, I'll take a PC12 over a Navajo any day. Navajos don't have the required single engine performance to maintain some of the MEAs here and you would be stuck in the icing layers single engine and soon share the same fate as a PC12.

A PC12 will get me over the rocks higher, give me more options to avoid icing, get me there faster (less exposure to bad terrain), and more reliably.


The other issue is, why should we have to regulate common sense? You can depart an airport below approach minimums, do any of you do that? What would be the problem with ensuring you have a suitable ceiling for SEIFR to ensure you break out at a manageable altitude? Or restrict your operations to 'cloud busting' IFR instead of hard IFR? The number of days you wouldn't be able to fly would be quite few in most parts of the country.

[Doc]

The day twin pilots do their check rides, from take-off to landing, with one feathered, I will feel safe in a twin.

Obviously you wouldn't take off with one shut down, but I'd be happy to shut it down after take off and fly you around for pretty much anything you could want to do on a ride, with one feathered. I can do approaches, overshoots, balked landings....anything you like, within reason on one.
It's really nothing special. Training departments, and flight schools make it harder than it need be. Just relax, fly the airplane and if you're a little slow, back off the power till the speed comes back. Maintain enough airspeed for a wee buffer...that's really it. The other "trick" is go wide, and give yourself lots of time.

Then, your my kind of guy! Take off downwind wind, on a gravel runway, up slope, at 8700 ft elevation, 35 degrees celcius, because the mountains ahead offer better SE obstacle clearance. But not much...

I did say..."within reason...." Where is this "set of the Sound of Music" to which your refer? Can't imagine too many places with an elevation of 8700 feet AND 35 degrees? That'd be a sea level temp of what? 47-51? Think I'd just drink cold beer that day and relax.

[Doc]

C337 vs C172...Ill take the 337.

Now, I don't disagree with you too often, but give me a 172 any day over the 337! LOL!

[Strega]

Its just my opinion but a properly trained crew in clapped out twin - I would put my family in.
I would not place my family in a SEIFR anything.

Couldnt have said it better myself.

[flyinthebug]

C337 vs C172...Ill take the 337.

Now, I don't disagree with you too often, but give me a 172 any day over the 337! LOL!

LOL Doc...well ok maybe that one was a stretch BUT i did do about 70 hours in one doing a moose count for the Sask Gov. It flew well and a rear engine failure you hardly even notice. Whats your beef with this fine "snort blow" Besides dont they say they are a 172 with a 2nd engine?