Turbo-Prop Derated Take-Off Power

[Bounceonland]

Hi,
just wondering :bored: : it's quite usual to use derated take off power in jets under appropriate conditions but it seems not to catch in T-Props, anyone knows why?
Thanks

[SNS3Guppy]

It's very common in turbopropeller airplanes, too, for a number of reasons ranging from retrofit and certification issues, to engine longevity, to the ability to maintain power to much higher altitudes. Both derates and flat rates are very common.

[Grizzle]

Dash 8 Q400 derates to 81% regularly, conditions permitting.

[Bounceonland]

Thanks, but where does one find the corresponding tables for power settings, i.e for PW 124 and 126 engines if not provided in AFM or runway analysis? Does each company have to make their own ones?

[18-Wheeler]

In the mob I work for, we can derate up to 10%.

[Gooneyone]

Bounceonland, to find the figures simply go into the power charts and use a high temp, such as 46C to get a takeoff Tq.
Then go into the Take Off Distances charts and get the TODR at that temperature and check your MTOW. If the weight is restricted, check at a lower temp. until you get a suitable MTOW, then apply that temp to the Tq chart.
Works very well for the PW 123 engines - up to an 8% reduction is the norm. It only gets difficult if there is an obstacle in the after take-off flight path.

[Cyclone733]

http://www.pprune.org/tech-log/292154-turbo-prop-derate.html

[Lookforshooter]

Is this with regard to corporate/charter or an airline operation?

[SNS3Guppy]

Does that matter?

[vakantieman]

all ATRs T/O with a derate of 10%. In case of an EFATO the remaining engine gets an automatic uptrim to 100 % T/O power (ATPCS system). If the ATPCS system fails, you set 100% T/O pwr manually after feathering the failed one.

happy landings

[Lookforshooter]

Yes Guppy it matters...because...according to Mutt, and all your buddies, the big argument for airliners using flex is to save engines. That argument only holds true when you airline guys finally let out the dirty little secret that your running your engines out to as much as 35000 hours. Now If I was looking at taking off, with a pair of 35000 hours engines, I would baby them too. Corporate typicaly doesn't do that, they rebuild at 3500 to 5000 hours. Exceptions do exis but since corporate engines are rebuilt so much sooner, we can run them right up to max on every take off, right up to overhaul, and we do...Flex take offs being just about non-existant in corporate/charter. So the question pertains to this very simple point: Does this question pertain to flying a turboprop airliner with 30000 hour engines, or a corporate charter operation with 2000 hours on the engines? Keep in mind Guppy, I am only using your info, so If I end up hanging it around your neck, don't blame me, it's the Socratic Method at work.

[Bounceonland]

Thanks for the inputs. Yes it is for airline ops with high hour engines and the other question remains on how to go about the distant obstacles below the flight path, clearway etc, since those are not to be found on the AFM graphs nor on any other charts carried in the plane that I know of.

Thanks again so far.

[SNS3Guppy]

Lookforshooter...ssg...tankdriver45...glockshuter...with the same, tired, ill informed message. So transparent.

Yes, corporate airplanes use reduced thrust takeoffs. I did it in the various corporate aircraft I flew, when I did corporate. I did it in turboprops and turbojets doing charter, ambulance, and other missions. I did it in firefighting aircraft, and I've done it flying privately. I've used derated, reduced thrust, assumed temperature, and other methods in aircraft ranging from the B-24/P4Y to the C-130 to the TPE331 and Pt6A powered Dromader to the Air tractor to the B747...and a lot of other equipment in between, such as the Learjet and Sabreliner.

The oldest FSI sim facility, incidentally, is for the sabreliner...and I went there when I flew the Sabre 60. Guess what...we did reduced thrust takeoffs, too. For all your expertise, you really don't know squat. FSI and Simuflite, where you claim to be a frequent resident, each teach assumed temperature reduced thrust takeoffs per the material put out by the respective manufacturers.

Flex, you don't understand and know nothing about...but it's a term you throw about indiscriminately and inappropriately (you apparently don't know where it applies, or why).

You alternately have claimed to be an airline pilot...and when that didn't work out, you claimed to be a corporate pilot and even an experienced helicopter pilot...but got shot down each time. Now you're a single pilot corporate pilot with "single pilot exemptions in six different citations." Yippee. Never the less, you seem to lack even the most basic understanding of turbojet operations (and fear turboprops because you "had a leak in the o-ring seal between lines in an oil pressure return line" in a king air, once. Very credible, you are. You were unaware that a turbojet even employed an oil return line, or that turbojet engines are susceptible to ice, yada, yada. And now you spout off on the same tired, ignorant, ill informed rant about reduced thrust, once again.

It might interest you (but it's doubtful) to know that derating isn't necessarily a means of simply reducing thrust for takeoff. Derating is often done as part of an engine installation. A piston engine replaced by a turbine engine, for example, will often see the turbine engine derated due to the structural limitations on the aiframe. The turbine engine can produce more torque, but it's derated to lower power settings, for lower torque, and enjoys increased life with lower temperatures, to boot.

We nearly always employed reduced thrust in the C-130. As we do in the 747. We do not compromise on runway distance, or on safety one iota. Our typical climb profile involves setting climb thrust at 1,000 above departure elevation; sometimes this means a thrust reduction, sometimes an increase...most often a reduction. All depends on our takeoff thrust setting. You seem to be of the misguided, inexperienced, and ill informed opinion that takeoff thrust ought to be giving it everything it's got...and that's utterly ridiculous. What it means is that you really have no idea what you're talking about.

Many turbine installations are flat rated. The engine will continue to make rated power up to a high altitude, where it's curtailed at lower altitudes. Many PT6A installations employ this practice. Including one you recently posted about in another thread...one which you knew nothing about, either.

That argument only holds true when you airline guys finally let out the dirty little secret that your running your engines out to as much as 35000 hours. Now If I was looking at taking off, with a pair of 35000 hours engines, I would baby them too. Corporate typicaly doesn't do that, they rebuild at 3500 to 5000 hours. Exceptions do exis but since corporate engines are rebuilt so much sooner, we can run them right up to max on every take off, right up to overhaul, and we do...Flex take offs being just about non-existant in corporate/charter.


Now you've claimed to have maintenance experience before; clearly you do not. Unlike you, however, I do. A lot of it. Many years of it. Mechanic, inspector, and I've worked the line, the overhaul shop, engine shops, repair stations, and twice been a director of maintenance. You may not be aware that many overhauled engines on corporate airplanes may have considerably more than 3,500 hours, or that by technical definition, an overhaul means inspected to ensure that all parts are in specification. An engine may be overahuled, and have not one single thing replaced...bet you didn't know that, did you?

A typical engine on an airframe on an airliner will have considerably more history and data on it's type than any corporate engine. While the TFE-731 is one of the single most widely used corporate engines, the number of hours on those powerplants pale in comparison to the total experience with the JT9D, for example. By orders of magnitude. What that means is there's considerable more data by which to base maintenance and inspection programs on many of the powerplants operated by an airline, with generally considerably more oversight. Manufacturers of smaller engines set limits applicable to their product, period. Manufacturers of larger powerplants set limits based on their product and the field experience with it. In other words, there's no "dirty little secret."

If it's a secret, it's apparently a secret only to you...and here you tried to come off as knowing what you're talking about, as an experienced soul instead of the microsoft flight simulator imposter you really are. It's a secret only to you...sort of embarassing to you, isn't it? If not, it ought to be.

A single powerplant on a large airliner can cost more than several of your corporate jets...especially the ones you claim to fly (I say that with a chuckle). Imagine replacing several of the airplanes you *claim* to fly, every 3,500 hours. Utter garbage. You fly throw away airplanes, do you? I don't fly throw-away engines.

A number of powerplants used in corporate aircraft, incidentally, have been run nonstop, that is never having been shutdown, for years. Decades, even. Bet you didn't know that, either. Not just stopped for overhaul and started up again...but run without interruption for years. PT6A's have been on the test stand without being shut down for 12 years, and PT6 installations in generators and other equipment have gone just as long and longer. They're not the only ones. The maintenance performed during that time? Oil was added. So much for being torn down every few hours.

They say a little knowledge is a dangerous thing. This is true, which makes you quite possibly one of the most dangerous men or women on the planet. Time to take your medicine, again.

Yes it is for airline ops with high hour engines and the other question remains on how to go about the distant obstacles below the flight path, clearway etc, since those are not to be found on the AFM graphs nor on any other charts carried in the plane that I know of.


You haven't specified what aircraft, but many airplanes I've flown, both corporate and otherwise, including my current mount, have data available for close-in obstacles and a host of other considerations...including reduced thrust using various systems such as assumed temperature.

Lacking some of that, no doubt you still have more than ample data to cover your operational needs. What are you flying?

[barit1]

Derate means a separate FAA/JAR certification of an airplane/engine combination - Separate AFM performance section, separate limitations perhaps.

FLEX is shorthand for Assumed Temperature Method (ATM) (aka reduced thrust), which may be applied to any airframe/engine combination. There are standing restrictions on use of ATM that you should be familiar with.

FLEX also requires that your operation have in place a condition monitoring system so an engine can't slowly deteriorate to the point that it won't make rated power. Do you have such a system?

The two (derate & ATM) are separate and distinct, but ATM may be applied on top of derate if conditions permit. Use pprune's search function and you'll find the subjects have been exhaustively covered many times. :)

[barit1]

Lookforshooter - How often do you fly a true performance-limited TO? That is, given the runway/pressure altutude/obstacles/OAT etc., you could not legally carry one pound more, for performance reasons?

If you ever did, and compared that to an average FLEX TO at standard day SL conditions, you'd find the FLEX TO gave you quite a bit more margin than the true performance-limited case. Why? Because your TAS (inertial speed - see Newton's third law) is lower because the wing is flying in cooler/denser air.

There's a science to this business, Lookforshooter, and name-calling does nothing to help your case.

[Bounceonland]

:ouch: Sorry Gents, if I knew this was going to cause such an emotional stirr I would not have asked.

( for what it's worth, I'm now in touch with P&W about it hoping to work out a procedure acceptable to CAA as well)

[barit1]

Bounceonland, sorry for the digression.

Turboprops set power by means of torque, right? And you have a table or chart of rated torque vs ambient temperature, right?

And if you look up your TOGW, PA, available runway etc. you can find the highest ambient temperature at which you can TO. Call this the flex temp.

Then go back to the power setting chart for that flex temp, and read the proper torque for that temp.

That's it in a nutshell.

[combineharvester]

Our Route Performance manual contains an extra page for each aerodrome with reduced torque settings (and V1 VR V2 speeds) for a given T.O.M for use in prevailing conditions where reduced power would be prudent. Aircraft is Saab 340B,
GE CT7-9B Engines, lowest figure i have seen in it is 86%. Max torque is obviously 100% however there is an extra 7% availiable from the engine in the single engine case. However due to some of the aerodromes on the network there are a lot of occasions where reduced power is not an option due RWY length/surface/terrain/obstacle performance issues.

[NonFlushingLav]

Barit: I can't remember the last time I ever took off with full fuel, or didn't need to reduce fuel to make second segment. Since I carry people, reduced thrust takeoffs are a luxury. I am always at max weight - people/Fuel. That said purposely extending my runway balanced field numbers into the stopway for the hope and prayer that the engine inspector will let me take those engines out a little longer seems counter intuitive. Trend monitoring is great for the parts that the inspector can see, but I had a #1 bearing failure at 35000 ft, at about 3300 hrs. No cause mentioned, just happened.

[SNS3Guppy]

There's a science to this business, Lookforshooter, and name-calling does nothing to help your case.


Perhaps now that he's been banned, the discussion can return to a professional track.

[NonFlushingLav]

How do you know he's banned...and I am curious..why was he?

[SNS3Guppy]

Two ways to know he's banned: the first is that it says "banned...persona non grata" under his name. That's always a good indication. The second is that you're here, easily identifiable as him...you're the same person, and as always, transparent both for your misunderstanding and your rhetoric.

Since I carry people, reduced thrust takeoffs are a luxury. I am always at max weight - people/Fuel. That said purposely extending my runway balanced field numbers into the stopway for the hope and prayer that the engine inspector will let me take those engines out a little longer seems counter intuitive.


That's a bit of a giveaway, righ there. You have a very poor misunderstanding of reduced thrust takeoffs, and constantly embarrass yourself in a crusade to prove you're right. These comments, that you can't do reduced thrust becuase you carry passengers, are clearly in error, and said in order to push the same tired, transparent agenda. Many of us fly passengers, and have done so for many years, safely using the manufacturer approved and provided data in full compliance with all the applicable regulations, safety practices and procedures, etc, using reduced thrust.

It's you. Painfully, obviously so...hiding behind yet another name because you don't have the maturity, the professionalism, nor the discipline to hold your tongue or have an informed, intelligent conversation.

You're "busted."

[NonFlushingLav]

With regard to my aviation credibility, I will say this...I do it for a living, and get paid well for it. That's enough I think for you or who you pretend to be. I am curious Guppy, if I am a recent reincarnation of someone your having problems with...how does he get back on? Ergo...what is the net effect of being banned, if he can come back at his pleasure and torture you at will?

[SNS3Guppy]

You just referred to yourself in the third person.

[G SXTY]

We de-rate all the time on the Q400 - and with passengers on board. :ok:

'Normal' t/o power (90% of rated torque) is actually used quite rarely, generally for first flight of the day or if specific performance related conditions apply.

For the great majority of flights, 81% torque is perfectly adequate - and it aint exactly underpowered.

[NonFlushingLav]

I guess it depends on the aircraft...if I flew an F16, I guess at 50% power I could probably climb out looking straight up. Not very interested in reduced thrust take offs that squeak over the fence, just to save corporate a buck. If I can reduce thrust, beat out that second segment climb gradiant with ease...sure why not...no sense having the passengers feel like they are in the space shuttle on climb out. Now just how many aircraft have all that excess power? Most are built to min performance spec to for fuel/range economy...not to mention weight.