Two questions to all you experienced pilots or engineers.
 

As the title says, I have two questions out there that I haven't been able to find an absolute answer to.

The first is in regards to the emergency power lever (EPL) in the C208.

Hypothetical Scenario.
You have got yourself into a situation through bad luck, bad piloting or just sheer muppetry that you find yourself confronted with a sheer cliff in front of you and you have NO OPTION but to try and out climb it.
The current max power setting will not give you enough to clear the cliff.

I understand the how the EPL works in general sense in that it bypasses the FCU and provides unmetered fuel to the engine. Extreme care must be used when using the EPL as it is very easy to exceed engine limits.
It stresses in the use of the EPL that the power lever must be in the idle position.

Which then brings me to my thought pattern.

If the power lever is open, will this then provide fuel via the FCU AND via the EPL?
If so, does this mean that should I need just that extra bit of power to clear the cliff that opening the EPL could increase the power?

Obviously the engine would require a full overhaul after exceeding its limits by that amount as I could imagine the gearbox and hot section would be a mess. But this is better than meeting my maker...


Question 2.

In the event of an overrun... If you had time, is it best to feather the prop or not?

I've heard some interesting theories in this and I would like to leave this up to you guys to discuss... one of the answers I got was pretty thought provoking.

No, absolutely no.


You are limited to the engine/prop torque, RPM and temperature limits. You cannot get more power. Using the EPL does not magically bypass or increase those limits.


I suspect that, with the EPL, the best you can get is only about 70-80% power. It is there to get you to an airfield in the event of a particular kind of failure in the FCU - not to give "extra" power to get over cliffs.

Once saw a PT6A started with the emergengy power switch (no, not a caravan) on. The annunciator catseye was closed. It shot straight up at the limiting temp. Not a good idea....

I must be missing something, but why feather?

If there are no obstacles, there's no problem.

But if there are obstacles, I'd be using the power lever right up until I regained control or was about to impact something, in which case I'd go for the red lever.

cough cough, wingover, cough

Exert directly from the flight manual contradicts what you have said:

! Caution
Inappropriate use of the emergency power lever may adversely affect engine operation and durability. Use of the emergency power lever during normal operation of the power lever may result in engine surges, or exceeding the ITT, Ng and torque limits.

That's the whole point of the "risk" of putting novices on a 114/A in the 208, there is nothing limiting you on the FCU from overtorquing / overtemping the engine to destruction.

Set at 1900 RPM and run up 2500 ft-lb. Using the horsepower calculation forumla thats 904 SHP. 114A is limited to 675SHP.

Thats an extra 229 SHP you just found yourself to try and miss that terrain.

The whole reason its vital to check the EPL is stowed correctly pre start is because if it's not, it's potentially allowing unmetered fuel in addition to the FCU and can cause an overtemp on light off. Again, the flight manual has specific warnings about this.

The same process dictates its going to keep adding unmetered fuel in addition to any fuel entering the mainfolds via the FCU and position you have the power lever set at while the engine is running.

I've personally discussed this scenario with a specialist PT6 engineer who has over 30 years experience on these engines, and his response was exactly as lilflyboy has suggested. If you are about to die and need the power, firewall the lot. The engine will be finished, but it will give you the power for however long it lasts.

The EPL is there for when the throttle linkage breaks and the power lever won't work any more. You won't get any more power out of the EPL that you would have with the throttle.

It's been a while since I've flown one but to memory that's how it worked. And yes if terrain is imminent then you firewall and hold your balls.

Secondly, why do you want to feather after an overrun?

RC.

I understand that the EPL is to be used in the event of an FCU failure.

I'm not meaning that you use the EPL instead of the power lever.

If the power lever was firewalled and the engine was producing full power from that.... if you then open the EPL, does it then introduce even more fuel to the mix resulting in an even higher tq?

Or will it result in a lower power setting? As far as I am aware if the FCU is functioning perfectly, and the EPL is then used... the FCU still provides the metered fuel to the engine while the EPL provides fuel as well. Hence the need for the power lever to be at idle while using the EPL. (Explanation of this was that in case it magically starts working again).

@Ultralights, you have never been shown how to do a wing over and the thought of doing one never entered your mind ;):p


@L0u0k0e Some people have suggested to feather the prop to try and preserve the engine. Obviously they have pulled the mixture too.

Be aware that rapidly advancing the EPL will flame out the engine. Just ask the instructor who had a student put the fire out off Cairns a few years back.

On the suggestion of using the EPL on top of the power lever, more fuel won't give unlimited power. The combustion chamber can only handle so much fuel...:cool:

Agree if you aren't going to survive without it, might as well pull everything you can out of the engine, stuff the damage. Equipment can be replaced, people can't. Was a caravan had an oil px light after take off from Beagle Bay WA several years back. Pilot shut down and feathered immediately and ended up with the aircraft arse up and the engine substantially further ahead of the aircraft on the ground. Could be argued they should have just flown the circuit back until the engine let go...

Exactly Makeit~

It's why I asked this particular question.
I only have one engine in front of me. While I do my best not to abuse it and treat it the best I possibly can... In the event that I do get myself into some form of trouble, I will fly that thing until it stops/disintegrates, if it will get me (And by proxy, my passengers) to safety.

I figured that the engine can only burn so much... but as a side effect of that... would that also then provide a cooling effect across the turbine like in a piston aircraft and enriching the mixture?

Its little tricks and tips like these that I am trying to store away for future reference in case its ever needed.

How about you just use good judgement and flightplanning to ensure you don't need these little tricks in the future?

Fly as per the flight manual and plan as per the regs. I've never had to go outside of the certified limits of any airframe or engine in 1000s of flight hours. GA, regionals and international airline ops.

Personally I'd never feather a prop unless the engine was not operational IN FLIGHT or during start/stop sequences. The feathered propeller will resist bending once contacting terra firma and cause an aircraft to flip. An unfeathered propeller will bend.

Having said that I'd do whatever the procedure in the QRH or flight manual told me. I wouldn't make it up as I go or use hanger talk procedures.

Thanks for that first useful bit of info there bluesky :rolleyes: People do make mistakes.

Take for example my current part of the world.
Take off on a down sloping runway, manage to get to flying speed and get airborne only to find that you have been overloaded for that strip due to someone lying on the weights on the manifest.
You find that you cannot outclimb the rising terrain nor maneuver left or right due to mountains either side of you.

Or a more realistic example, you are at max landing weight into a strip that is at 7,000ft. A aircraft or solid object like a car or truck enters the runway and you go around and try to climb up the valley with hills all around you. You can't outclimb the rising terrain.

There is ALWAYS exceptions to the rules and events that take place in aviation that we CANNOT plan for. I'm sure in your 1000's of hours of flying, you have had one or two events where things did not go as planned. If not, then you have had a very lucky career thus far.



As for the feathered prop thing, thats exactly what I was looking for.
Although I'm not sure about flipping the aircraft? I've heard that instead of that it ends up snapping crankshafts and tearing engines from engine mounts.
People are trying to save engines by feathering the prop before impact but end up doing a lot more damage structurally.
I know that I for one once had a young instructor try to tell me it was better to feather before the accident to try and save the engine if you can.

kingRB,


I don't think you know much about how the PT6 engines work - despite your claiming to have had discussions with a PT6 engineer. This statement gives you away:


"unmetered fuel"? There is no such thing on a PT6. "manifolds"? There is no such thing on a PT6. You are thinking of a piston engine!


Are you saying you can actually do this in a C208? That would be a gross over-torque. Does that engine not have a torque limiter? Every PT6 variant I have flown has had a torque limiter.


Here is a little test for you. What does the power lever actually control? What does it actually do?

Haha really? Not sure if trolling or actually serious....

The FCU has a fuel metering section, a temperature compensating section and a Ng pneumatic governor. Using the EPL bypasses all of these in the typical case of a P3 failure or any other reason the FCU may stop working correctly. Hence why I said "unmetered fuel".

The PT6 114/114A actually has 2 fuel manifolds, a primary and a secondary after the flow divider.

If you don't think PT6's have manifolds, then i'd like to hear your explanation how fuel is delivered to the nozzles in the combustion chamber...

Yes, you can do it, i've seen a newly endorsed pilot do it. No, it does not have any limiter which will stop you overtorquing via the power lever.

perhaps you are the one needing to brush up on what the power lever does :ok:

kingRB,


I've found some material on the 114 engine, and agree that, unlike other variants of the PT6 engine, the 114 does not have a torque limiter.


The only limiter is the "secondary governor" which limits prop RPM in the event of overspeed. It works by limiting fuel flow from the FCU, so this action would be bypassed in the event of EPL use.


This is the only protection that is not available with EPL use. What other protections does the engine have? None - there are no other protections. There is no torque limiter, and there is nothing to limit Ng or ITT.


So, what this all means is that you can use the power lever to exceed normal engine limits and get that extra power. No need to use the EPL.


Wrong. The only place the engine gets fuel from is the FCU. That fuel is always "metered". The difference with EPL use is in how the metering is done. Your statement could be considered correct in a functional sense, but that functional sense tends to imply that the EPL is providing fuel by an alternative source that exists alongside the normal source - hence the idea by the OP that you can get extra fuel via the EPL, and this is wrong.


Ok, so we don't know what the power lever does! Sure, we know what happens when we move it - pushing it forward results in an increase in torque, ITT and Ng, but how does it make the engine do those things? The reason I ask is because if you knew, it would be very clear that there is one source of fuel to the engine, and that this fuel is always metered. You would also know where the EPL fits into the scheme.


Have another go.

I am not giving any advice on this as it is years since I flew similar engines. However Lilflyboy I understand your question and Blueskymine despite meticulous flight planning situations do arise. I got stuck in a downdraught coming out of a Swiss airfield and had to pull out all the stops to get over a ridge. It was called water metanol!

So you want to argue semantics now , but on the premise I apparently don't know much about how a PT6 works... :D

As I just said, the EPL system bypasses the fuel metering section of the FCU. Since you need me to clarify this: It does so by directly controlling the fuel metering valve. If fuel is being sent to the engine that is not being governed by the metering system in the FCU, then I believe that would pretty much make it "unmetered".

Hence the warnings by the manufacturer to ensure you do not have the EPL anywhere other than in the normal position when starting or operating the engine under normal conditions. It's possibly sending more fuel to the manifolds than what the FCU would normally be doing by itself.

In hindsight looking at my original post, I should have said "allowing" instead of "adding"... I'm so glad you picked up on the crucial error.

None of which you've addressed above provides any evidence that the EPL will not provide extra power if used in conjunction with the NPL which has been firewalled.

Again, the manufacturers warnings would suggest that it can.

BTW, still awaiting the explanation on how the PT6 doesn't have any manifolds...

I'm guessing that this means that if the EPL was wide open... then the metering valve would be wide open also.
Would the valve be in a similar position if the normal power lever was opened fully?

King RB you are hitting the nail on the head.
FGV you are reading the B200 manual there is no fuel limiting system in the 114.
Romeo Charlie if you have a C208 endo please return it to the person who gave it to you... Only used if the throttle linkage breaks? I really hope you have never flown a 208.

Looking at the diagrams I believe you would end up with more fuel and therefore more TQ but you would be pushing an engine right through the limit. If you can't get out of it by firewalling the power lever do what you have to.

As for feathering the prop... What happens if you are stopped on a taxiway and you take your feat off the brakes and feather the prop? It moves forward due to the prop moving from the fine pitch stops to the feather position. So if you are trying to slow down in the event of an overrun why would you feather? If you hit something with the engine running feathered or not you are going to destroy the gear box and probably the power and compressor turbine.

Answer the Question!!!!!!!
 

I cant handle this!!! :ugh: In a normally functioning C208 just push the power lever as far as it will go to get over your imaginary obstacle. It will give you all its got and yes the engine will be a boat anchor when you are finished. Forget the EPL unless your FCU has died.

Secondly do not feather the prop. Even a windmilling prop will provide far more deceleration then a feathered one. Just ask the guy who bent a new Caravan at Caloundra a few years ago. Either way in this type of event the Insurance company owns the aircraft and you need to do what is required to save your butt.

Groggy