As always there is the "for" and "against" camps........I wonder how many would be so enthusiastic in their objections to SE IMC...the PC12....C208...TBM 700, if they had actually operated them?
Ive flown 402's......Navajo/Cheiftains....PA23's etc...., and Ive also flown C208's, PC12...and been right seat in a TBM700..and I'm damn sure I feel safer...I know im more likely to walk away if anything goes wrong.....and have less of a chance of experiencing an engine related problem in a single turbine, thats not only my opinion..its a statistical fact.

Yes if it goes quiet..you go down.......but in most cases you force-land with less forward velocity than your average motorway accident....in a far more crashworthy environment.

H:ok:

DJohnsen wrote:

Yes, supposedly. The information comes from a person who was in the presence of the owner/pilot when the news broke via cell phone. And you're right; it is a very intriguing development if the story can be verified.

FOF

Yes......but.
 

Tinstaafl

Correct, but only up to a point. GA twins lack certification for engine out performance and consequently require near perfect technique to stay airborne once the inevitable happens. Navajos, Senecas and even the humble Aztec can hold their own after engine failure but perfect technique, for various reasons, isn't always applied. Your stated 'rolling inverted & spearing in' scenario becomes the end result. Aircraft are standard issued with a rudder, the pilot similar with a foot. Use of both is mandatory to squeeze any benefit from the second engine.


The post by Carrier illustrates the argument rather well. SE turbine aircraft manufacturers, civilian and possibly military, would appear to let bubbling enthusiasm for the product lead to over optimistic claims for the relative merits.

Panama Jack

I think you might be wrong about there being no fatal PC12 accidents. As far as I know there was a fatal assymetric flap accident a number of years back that led to a re-design of the flap system.

"...GA twins lack certification for engine out performance and consequently require near perfect technique to stay airborne once the inevitable happens..."

And that's the crux of the risk. Single engine a/c don't have the severely degraded handling qualities of light twins, nor does the pilot have to make a rapid decision about whether the a/c is capable of flight (it's not guaranteed, remember, although it might be required to have some amount of performance under very strictly limited conditions. Depends on the certification of the type).

The upshot of the figures used by Oz CASA was:

* S/e turbine very rarely have an engine failure where as they're relatively more common in light piston twins.

* Engine failure in a single nearly always results in a forced landing/crash but not so in the light twin.

* Of the a/c that have a forced landing/crash, the s/e case has a lower fatality rate than the twin, due to not having a loss of control factor and also having a lower speed.

So, in the light twin you're less likely to have a forced landing as a result of an engine failure however, of those that do result in a forced landing/crash you're more likely to die.

The overall risk of a fatality in the SET is equal to or better than the light twin.


***All the above quoted from memory of the CASA document(s) ~10 years ago so blame me for any errors.

http://www.atsb.gov.au/aviation/occu...ail.cfm?ID=315 is a good example of what the pc12 won't do.

cs

The Van might use gravity feed to supply the FCU, but recall a high pressure pump circa 650-750psi is an intregal part of the FCU and when it goes...the engine flames out...similar to most turbine engines the pt-6 requires highly atomized fuel to operate...like an injection pump in a diesel engine...same concept......

Bobknowledgy.
Sadly I know of at least one fatal PC12 crash. Late 80's into the back of the Ngong Hill's near Nairobi. Admitedly not engine failure, and was CFIT, so could have happened in anything.
However, with regards to all the engine failures on PT6's in Africa, although it will outrage all the blokes flying them there, a lot of the problem is how they are operating them. Some operators have the problems, others dont. There was a saying when I was there, when asking about the best way to operate a PT6... there are as many ways to operate a PT6 as there are pilots flying them.
The fact is in single pilot ops, with thin SOP's to say the least, people tend to develop their own 'tricks'. As engines come in for inspections and overhauls, the engineers can see whats been done to the engines. We were on the cessna trend monitoring, and the boss could (can) see who cooked the engine on what flight, so we were very conscious (sorry, spelling) of running the engine within company limits inside manufacturers limits. We were new to turbines, and managed to operate the C208 as well as anyone else, and managed to get overhaul extensions from Cessna with no problems. Much easier to keep track of an engine with only a very few pilots flying it.
Didn't mean to annoy anyone, but it is a bit of defense for the PT6.

It was hard to tell what exactly the cause of the problem was, however, in light of the mot recent notice from PWC regarding power roll backs, and presuming that this was the problem, could the pilot not have used the Manual Over Ride (MOR) and fly the aircraft back to the airport for a "safe" landing?

Actually, this accident occured in February 1998 (a/c ZS-OFC).

The PC12's first flight was in 1991.

There were four power roll backs that prompted the P &W/Pilatus inquiries. Two of the roll back events occurred on the ground and the engines flamed out very rapidly. The other two events occurred inflight and in both cases there was sufficient time to recover the Ng with the MOR and land safely; however, in at least one of the cases, the lever was moved too rapidly and the engine was badly overtemped - twice.

As for the Indiana plane, I'm sure we'll know the cause eventually, but right now all anyone can do is speculate. The failure supposedly occurred at 7000' as I recall. That might have been low enough to allow for a rapid roll back. Pilatus is currently collecting data on the rate at which roll backs can occur at different altitudes in order to give better guidance as to the use of the MOR on the PC-12 installation.

My understanding of the power roll-back scenerio is the result of a failure of the FCU unit. In this case the engine will not flame out, but "slowly" roll-back to an idle speed below normal ground idle speed, approximately 40% Ng. The use of the MOR will then deliver raw fuel to the engine, bypassing the FCU altogether, and allow the engine to accelerate to normal operating speed. Of course, as mentioned previously, there is a very high chance of over temping the engine as the rate at which fuel is delivered to the engine is no longer governed by the FCU, but by the pilot.

I'm not saying pilots are to blame, I'm just indicating that the MOR is an extremely sensitive controllever that one cannot advance as rapidly as a Power Lever and that in an emergency situation where the adrenaline is flowing, the tendency to advance the MOR too quikly is very prevalent.

Anyway, should my understanding of the situation be correct, then why did the engine flame out?

It depends upon the altitude and airspeed at the time of the roll back. At 30,000', the roll back is slow and stabilizes at about 70% Ng. As altitude decreases, the rate of the roll back increases and the Ng at which the engine stabilizes decreases. At lower airspeeds, roll back will be faster and Ng stabilization lower (if it stabilizes at all) due to decreased airflow. The flame-outs occurred on the ground, in ground idle, during taxi.

You're right about the sensitivity of the MOR. I recently saw a video of a Pilatus test pilot simulating a Py failure in flight at low altitude. The rapid roll back sneaks up on him and he tries to recover by moving the MOR lever too quickly. Realizing his mistake, he pulls the MOR lever aft, but it is too late and ITT rockets beyond 1000 degrees C. The engine was inspected upon landing and no damage was found. Even though the test pilot was expecting the roll back it dropped below 50% Ng before he could catch it; the average pilot would probably not recognize the problem until well after the event was unrecoverable.

But that is the reason they are doing the testing, to find out what the rate of roll back is for various combinations of altitude and airspeed. And since it takes about seven seconds (on average) for the MOR to become effective, hopefully they can provide some guidance as to when the airplane is too low or slow to recover Ng.

Full of Foehn,

Thanks for the explanation. I was not aware of the difference in roll-back rates vs. your altitude and speed, however it does make sense. What is the most interesting though, is the fact that these test have not already been conducted and the result/figures published!?!? These single engine turbo props are not new investions, they have been around since the 80's, and more and more are coming. So why has the average pilot been lead to believe that there a/c is equiped with a back-up system to over-ride an FCU in the event of a failure when in fact should the FCU fail, it would happen so quickly that catching the failure would be next to impossible, especially at lower altitudes??? ...It's an interestig situation that we have here. I'm interested in hearing more.

Cheers,

Joe

Smallfry
I agree that with no or minimum SOP's low hour turbine pilots will operate the PT6's as demo'd during their conversions, and then the rest is hands on so to speak, ie: each pilot will have his own idea on engine operations.

Reading a resent magazine article, owners of aircraft on charter in the area you mention are now hooking up their ac to their computers at work via satellite. Thus they can see where their a/c are at any moment, and can do their own engine trend monitoring, knowing figures haven't been tweeked.
For the record, I'd be happier in a SE Turbine than a ME piston, IFR or night. Obviously, ME was better for the logbook when hour chasing.

Hi all

I used to fly Twotters for a number of years fitted with the PT-6-27R engine. As I recall, this had an engine driven fuel pump and standby pump for each engine. On faliure of the engine driven pump, the pressure loss detected downstream in the fuel lines would automatically activate the standby boost pump. If this didn't happen, the engine flamed out, but could then be restarted using a manual selection of the standby pump on the emergency panel. The standby pump was more than able to keep the engine running at all power settings on it's own, although in the UK we were limited to max operating altitude of 8000 feet.

Is this not the case with the larger PT-6s as fitted to the PC-12? If so, is this not like taking two steps backwards in design, having no suitable means of redundancy?

The PT6-67B on the PC-12 has a similar configuration; wherein, the loss of the low pressure engine driven pump (43 psi output) can be replaced by fuel boost pumps (31 psi output) located in the fuel tanks. If fuel pressure drops below 2 psi (possible low pressure pump failure or clogged filter), the boost pumps are automatically activated to continuously provide fuel to the high pressure pump.

However, the high pressure pump (800 psi at 100% Ng) that supplies fuel to the FCU has no redundant system. I think most PT6 installations are so configured (anybody?). I guess you'd have to ask Pratt about the engineering logic behind this single point of failure.

FoF