Pilatus PC-12's
 

Was having a chat with a fellow pilot a couple weeks ago about Pilatus PC-12's. It seems to be an overall impressive aircraft with impressive economics. The PT-6 powerplant is one of the most reliable and proven engines, and the aircraft operates on behalf of some serious organizations in some very demanding roles in unforgiving environments(Royal Canadian Mounted Police operates them in the Arctic, Royal Doctor's Flying Service operates them in the outback of Austalia, etc.) Pilatus continually points out that PT-6 powerplant failures are pretty much unheard of and that the engine-out glide characteristics should leave a pilot with a few options up his sleeve if it should happen.

Yet after my conversation with my colleague, and after reading the following articleon AvWeb, I've been pondering this issue:

As my colleague pointed out, the real weakness isn't the PT-6 powerplant, but rather the High Pressure (Engine Driven) Fuel Pump (of which the PC-12 only has one). Lose the HP Fuel Pump= loss of the engine. The low-pressure boost pump does not even approach the pressure required to keep the engine running. I'm not an engineer, but could Pilatus or Pratt & Whitney have designed redundancy into this system by providing for two HP Fuel Pumps?

This is the second PC-12 power loss accident that I am aware of-- the other one occured a few years ago in Newfoundland, Canada, to one owned and operated by V Kelner Airways (who ironically is the Pilatus dealer in Canada).

Any thoughts? :confused:

If they'ed been operating a Caravan.......he could have pulled up over the power lines...done a touch and go on the road...then finally landed back at the field.....Vans are good gliders:p cept when theres a bit of ice about.

Seriously though...this problem cant be as simple as a fuel pump failure?.....(the van uses GRAVITY)...most GA A/C ive operated utilise the LP pump as a standard fuel feed...with the HP pump used at times of exceptional demand.

Am I wrong or what?

In all civil turbine engines that I have operated (including the PT6..as far back as 1966) require an engine driven fuel pump/fuel control unit to feed fuel to the burner cans, for combustion.
EDP/FCU fails...engine goes quiet.

Had this happen on a 707 one time...and the fire went promptly out.

This clearly is not a good thing if you only have one powerplant.
Another failure that a PT6 can have is a prop governor failure.
I personally experienced one many years ago on a BE99 (governor pilot shaft separated), and the prop feathers, due to a lack of oil pressure to same, altho the gas generator continues to function.

haughtney 1 - I think that you would be surprised at how well a PC12 glides. It staggered me when I did my training in it.

Oh - PJ you missed the one off the Russian coast near Sakhalin Island.

But if you have a read of the accident reports, it could hardly be put fairly and squarely on the feet of the PT6/PC12 design.

Think about the number of major accidents (usually Vmca related) are caused by taking off in a Kingair (FAR23) and having it go silent at an awkward moment? And there's twice the chance....

411 my apologies.....LP pump=EDP......and on the 114 version of the PT6 we have a FCU overide..basically it throws raw fuel into the turbine..(fine as long as the pwr lever is at idle..otherwise barbeque time!)

Compressor...I see your in WA...are you flying RFDS?.....or for Air Nigu..thingi ma jig..(aboriginal air services?)...just being nosey.

Im thinking of applying in any case......Europe has crappy winters!

Yep, the former, although I left there recently for other climes. Last I heard Air Nguimaniniguinamingui had sold their PC12 to Police Air Wing in Alice Springs.

And there is the MOR lever on the -67B.

Compressor check your Pms..please


:ok:

Hey jack. The bear had a few, RCMP had one on takeoff, and I know of another that was found making metal and was pulled out just in time. I've logged over 2000 hrs of PIC and never had engine problems. A different way of planning and executing approaches, climbouts, etc makes one feel more secure. But, if you aren't comfortable flying a single IFR then you shouldn't be flying one period. Great aircraft, not too bad engine.

Panama Jack, and any others interested, I suggest you look at some other threads on PPRuNe.

First look at “Van has engine failure in Tanzania” in the African Aviation forum. In particular look at Shenzi Rubani’s post in that thread on 21 October 2004. Eight Caravans going down in a one year span because of engine failure indicates that the PT6 is not as reliable as P&WC and some operators would have us believe. You will note that the aircraft belonged to different operators in different countries so blame cannot be attached to one outfit’s operating procedures or maintenance standards. The only common factor is the PT6. You might also look at the thread earlier this year entitled “Van down in Tanz”. In addition to the Caravans, there have been other single turbine engined aircraft, such as the PC12 you mentioned, going down in the same time frame because of engine failure. In the face of this evidence in only single engined aircraft it is difficult to see how Pilatus can claim that PT6 powerplant failures are pretty much unheard of!

If you have only one engine, when it all goes quiet at the front it does not matter what fuel that engine was using. You are still going down and are dependant on there being a suitable landing site within gliding range and on the pilot’s skill to get you safely on to that site! This assumes the pilot is able to see the landing site, which is most unlikely at night or in serious IMC. As Shenzi Rubani mentions, there have been engine failures in King Airs, etc in the same time frame but they do not show up in the accident statistics because the second engine enabled their pilots to get them safely back to a proper airfield.

To give credit where it is due, the PT6 is a wonderfully reliable engine. However, it is not infallible and its failure rate is high enough to be of serious concern for single engined passenger carrying use, such that single turbine (as well as piston) engined aircraft should not be permitted to carry fare paying passengers in IMC, at night or over water or inhospitable terrain. I see no problem with the use of single turbine engined aircraft by freight or private operators, whose pilots and occupants presumably know of and accept the additional risk. Similarly, I have not heard anything negative on either the PC12 or the Caravan. Both seem to be great aircraft that do an honest job. There has been some mention of airframe icing on Caravans but I suspect this is due to Caravans being regularly used in some pretty harsh climates. Any other type of aircraft used regularly in such climates will also suffer icing more often than if used in a mild climate. The only problem I have with both aircraft is that they have only one engine, which to me indicates that their operations when carrying the paying public should be limited as outlined above.

Second, look at the thread earlier this year on the Canada forum regarding Bearskin Airlines and the PC12. Some years ago Bearskin introduced some PC12s to replace some of their King Airs and similar aircraft. Now it seems they have been getting rid of the PC12s. There must be a reason. Perhaps it would be worth your while to contact Bearskin management or pilots, perhaps initially via a post on the Canada forum, to find out why this change is happening. If you find out by means other than PPRuNe, please post it on PPRuNe. I have also been wondering why this change is taking place at Bearskin.

Hope the above helps.

Thanks for having taken the time to write that information, Carrier. There has been a discussion going on also at the AvCanada Forum about the Pilatus PC-12 with many comments echoing your concerns.

AvCanada Forum Thread

What I found interesting was that up until now there have been no fatal accidents involving the PC-12, due in part to the low stall/approach speeds as well as the crash survivability designed into the aircraft-- a real advance compared to GA designs from a few decades ago.

I have to admit to being a PC-12 fan, and although I agree with all statements made by Carrier, I also have concern at the number of fatalities and serious injuries of the years, due to assymetric operations after an engine out (many while training).

There are pro's and cons for all designs.

Centreline thrust works well - Cessna 337. Maybe we should only fly in jets with 2 or more engines at the rear... obviously Dassault have that equation right!

At the end of the day, it's horses for courses... I love flying fixed and rotary wing, but as far as safety goes, I would prefer in order of preference, single engine turbine, twin engine turbine rotary, single turbine rotary, twin piston fixed, single piston rotary, single piston fixed (unless ballistic shute fitted, then it's probably up the front!)

I specialise in risk management, and at the end of the day, its a risk assessment that we all make, as a pilot, and as a passenger, depending on where we are in our career or what we can afford!

I am sure if there was no such thing as economics, we would be flying around in 4 engined aircraft that stalled at 20kts!

bobk

Thanks Panama Jack for supplying link to Canadian Forum thread.

I read through the thread, and although there was much critisism by those "boys" not flying the aircraft, the pilots that were, had nothing but praise for the aircraft, and the stats speak for themselves - out of all the engine-outs, there have been no Pilatus fatalities, and they seem to float well!:O

Playing the devils advocate..just for a moment...(if there have been no fatalities) the a/c is safer than a 737, 747, DC-10, A320..purely on that point alone.
I believe the problem lies in the perception that with only one engine...it quits...your dead, when plainly with the PC-12, all the engine failure issues have been non fatal, in the same time that the PC-12 has been around...how many turbo-prop twins, piston twins have crashed fatality after engine failures? A Shorts 360 going in after a double engine failure immediately springs to mind...back in about 1998.
Both viewpoints...for and against are diametrically opposed...the thing that I find interesting about all of this is....most of those that operate SET..i.e. PC-12, C208, TBM700 etc....have got nothing but praise from an operational point of view..as long as the a/c are operated in the roles for which they were intended and designed to do. It is invariably when the margins are pushed..or exceeded...that problems have occured.
Finally, just for the record..Im much happier IMC in a SET...than say a Navajo, or C402, the type of general aviation a/c the SET was designed to replace.


:ok:

According to Pratt there are no engine failures on record attributable to HP fuel pump malfunction. However, Pratt and Whitney issued a Service Information Letter in September 2004 regarding power roll backs in the PC12. The cause of the power losses were attributed to a defect in the copper-beryllium bellows in the FCU that resulted in a leak in the bellows assembly. Although the bellows is common to many PT6 variants, the Cu/Be bellows is unique to single engine installations to accommodate the MOR.

Pilatus is currently collecting data on the roll backs and MOR operation procedures will likely be modified. They have found that at low altitude some of the roll backs due to Py leaks are very rapid and probably not recoverable by MOR operation.

I can only speculate about the plane in Indiana, but I'm sure the FCU is a suspect for the “engine malfunction.”

Also, rumor has it the PC12 that went down in the Sea of Okhotsk in 2001 washed a shore in Russia last November. The owner/pilot was reportedly very unhappy upon hearing the news. If true, it is astonishing that the airframe floated for so long, especially in light of the report that the pilot and pax exited the plane through the cabin door allowing water in to the cabin and cockpit.

I would have thought the owner would be at least mildly happy about the Swiss flotsam coming ashore. Unless, he had reason to want it to sink, or perhaps this complicates insurance issues; maybe he was just done with it. I don't know. I'm sure Pratt and Pilatus are quite pleased the plane has surfaced (so to speak).

Has anybody else heard this rumor?

Was it a PC 12 or a Phantom ?:E

I've experienced two in- flight failures of the PT-6: a severed oil-line (EMB-110) and a failure in the interstage bleed valve which prevented engine acceleration from flight idle (SD-360).

If it can fail then it will. Whether powered by turbo- fan, turbo- jet, turbo-prop or rubber band the mathematics are inescapable. One minus one equals zero, down you go...... simple as that.

'Down you go' is true *however* you don't tend to do it after rolling inverted & spearing in, which is an unfortunately common theme in light piston twins. Of the two, s/e failures that result in a crash tend to be more survivable.

I wish I had kept CASA's discussion paper when puplic transport SETO was first mooted. As I recall the risk was similar or better for the s/e turbine because, even though a forced landing was nearly guaranteed, they had virtually none of the loss of control related prangs experienced by the twins AND the likelyhood of a failure was much less.

Does anyone still have a copy of that paper? It doesn't seem to be available online at CASA, only selected quotes in the follow on documents in the reg. reform process.

Didn't a Caravan pilot face a (Pratt&Whitney) flameout near Alaska whereby the prop went into a fairly flat pitch and he was forced to push the plane almost straight down in order to keep it above minimum clean flying speed, and he ditched it somewhere?

Strange prop malfunction, if this is true.:eek:

Anyone else heard the rumour about the PC-12 washing ashore in Russia?

Very intriguing.

A few years ago a PC12 experienced engine trouble somewhere off the coast of Japan and ditched. The crew was rescued within a few hours and the aircraft was last seen floating away...? There were to my knowledge no attempts to recover the aircraft, assuming it would eventually sink. Did this aircraft actually reach the Russian shore?

Dag

Tinstaafl

Well said

Plus people tend not to know that if you are certificating a single engined aeroplane it must have a max stall speed of 61 kts. There is no such limit on the stall speed of multis and many are considerably higher. Given the v squared issues of a landing v matters too!

Regards John

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