Derated engines
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Always fun to come here and talk to guys that don't think....
Wow, there are still some that answer to ssg posts?
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NO BODY cares about the whining outside of the aircraft. If you are given a servicable aircraft with all other factors in check, TAKE IT OR LEAVE IT! Your choice. I have strapped into several aircraft that the customer lied about the load, Happy to say it was an MD-11 and we did not notice until 5-6 hrs into flight monitoring fuel trend. The culture here, drivers scared of their own shadows is rediculous. Hey for half a decade I did 3 legs for every one you were assigned and fully involved with most aspects of the flight, technally. Grow a friggin pair, educate yourself. Rant quits now, trust your machine and the people that certify it. It is your JOB, walk away and pick a fight if you have the grounds to stand on, if not STFU!
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per Sillypeoples -
I'm sure, with your vast knowledge of all things aeronautical, you can quote for us a few airlines operating their engines per standard overhaul times 
The manufacturer has derated the engines so far anyway for normal ops to pretty much guarantee that they will go double typical standard overhaul times....
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So what you guys are saying is that if I take off in a corporate BBJ at max take off that's dangerious.But if I take off in a 737 using reduced thrust, that's safe. So if I burn up a 10,000 ft runway in a 737 using reduced thrust...that's safe...But if I burn up 5000 feet of runway, with plenty to spare ahead, incase something goes wrong...that's dangerous.lol.Coming here is always good for a laugh....the way you guys think is beyond Orwellian in it's group think/no think.
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No, I'm not saying that at all. The statistics on EFATO (or RTO) show little effect of full vs reduced thrust. For all I care, you are welcome to thrash those mules every takeoff, because you'll be pulling engines off wing sooner, and consuming more HS parts every time. This increase in parts sales can only benefit my employer and my pension. 
Thank you!
Thank you!
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Incidentally, check your engine warranty with CFMI. You may find fuel burn clauses, and EGT deterioration clauses, and other warranties wherein CFMI reimburses for poor performance.
But you the operator has to hold up your end of the bargain - average thrust reduction of xx%, periodic NDT inspections, etc.
But you the operator has to hold up your end of the bargain - average thrust reduction of xx%, periodic NDT inspections, etc.
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Coming here is always good for a laugh
the way you guys think is beyond Orwellian in it's group think/no think
The intellectually challenged will always have a problem understanding the issues involved, we can direct you to services.
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Brian...how you are tolerated here as someone that is involved in aviation is beyond me...another piece of fruit or nut in the PPRUNE fruitcake. Well Xmas is coming up isn't it....
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Not sure if has been raised but for the examples given regarding varying thrust ratings of say a CFM56 be it a -3 or -7, I seem to recall that depending on the thrust rating chosen this dictates the TBO of certain components within the engine, e.g turbine discs etc.
The higher the thrust rating set the lower the TBO.
The higher the thrust rating set the lower the TBO.
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Parts life vs rating
Bumpfoh -
This may well be true for CFM56 - can't say for sure.
However I know that 747SR (high density seating, lower fuel load, optimized for high cycle short range ops) had its engines de-rated something like 10%. JAL and ANA were big customers. The fallout from this type of ops was extended parts life. I don't think there's any reason this shouldn't extend to the CFM56.
This may well be true for CFM56 - can't say for sure.
However I know that 747SR (high density seating, lower fuel load, optimized for high cycle short range ops) had its engines de-rated something like 10%. JAL and ANA were big customers. The fallout from this type of ops was extended parts life. I don't think there's any reason this shouldn't extend to the CFM56.
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I have read about incorrect numbers being used when calculating reduced thrust that have resulted in close calls on takeoff, so being ready to push the levers forward if not happy with the takeoff performance is not a bad idea. I have had errors in loading (up to 20,000 pound in the 747 and 2000 Kg in a 748, which as everyone knows is an improvement on the 747) that would have been quite a problem if I had used reduced thrust at the time. I personally add .02 EPR to any reduced thrust calculation to cover instrument error!
Full thrust takeoffs and max power climbs, max cruise settings at the highest altitudes will save on fuel. With fuel costs so high, it might be necessary to scale back on reduced thrust takeoffs.
The reason for reduced thrust is to reduce engine wear, and the biggest cause of wear is temperature. The argument is that it is most important to keep the EGT/ITT as low as possible. But reduced thrust means that the takeoff rating has to be held for a longer period. Has a study been made to determine whether a single high temperature limit held for a short period does more damage than a lower number for a longer period of time? Maybe the only reduction that needs to be made is a small one, just to keep the temps away from peak, rather than the large reductions we use now, but have to hold for longer periods.
And that always gets me back to the argument about flap. Using Flap 10, say in a B744 instead of flap 20, gets the airplane off the ground and up to the point at which climb thrust can be set in a shorter time. This would lead to less engine wear, but most airlines will not even consider it.
Full thrust takeoffs and max power climbs, max cruise settings at the highest altitudes will save on fuel. With fuel costs so high, it might be necessary to scale back on reduced thrust takeoffs.
The reason for reduced thrust is to reduce engine wear, and the biggest cause of wear is temperature. The argument is that it is most important to keep the EGT/ITT as low as possible. But reduced thrust means that the takeoff rating has to be held for a longer period. Has a study been made to determine whether a single high temperature limit held for a short period does more damage than a lower number for a longer period of time? Maybe the only reduction that needs to be made is a small one, just to keep the temps away from peak, rather than the large reductions we use now, but have to hold for longer periods.
And that always gets me back to the argument about flap. Using Flap 10, say in a B744 instead of flap 20, gets the airplane off the ground and up to the point at which climb thrust can be set in a shorter time. This would lead to less engine wear, but most airlines will not even consider it.
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But reduced thrust means that the takeoff rating has to be held for a longer period.
Last edited by Denti; 1st Dec 2012 at 19:14.
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boofhead:
True, when you consider only that one flight..
But the legacy of that one flight, and a few dozen more of the same, is an engine with reduced efficiency and it perhaps burns a percent more fuel as long it remains on wing. So long-term fuel conservation does not follow from your suggested protocol.
But the worst element of deterioration is definitely takeoff. The transient from idle EGT to takeoff - several hundred degrees in a few seconds - carries with it the risk of rubs, etc. Anything which reduces the rate and magnitude of the EGT transient helps mitigate engine deterioration.
But after TO power (derate or reduced) has been set, and run stably for a minute or two, then using max climb is a (by comparison) small EGT transient. Most engine folks would say "be my guest" re max climb thrust.
Full thrust takeoffs and max power climbs, max cruise settings at the highest altitudes will save on fuel. With fuel costs so high, it might be necessary to scale back on reduced thrust takeoffs.
But the legacy of that one flight, and a few dozen more of the same, is an engine with reduced efficiency and it perhaps burns a percent more fuel as long it remains on wing. So long-term fuel conservation does not follow from your suggested protocol.
But the worst element of deterioration is definitely takeoff. The transient from idle EGT to takeoff - several hundred degrees in a few seconds - carries with it the risk of rubs, etc. Anything which reduces the rate and magnitude of the EGT transient helps mitigate engine deterioration.
But after TO power (derate or reduced) has been set, and run stably for a minute or two, then using max climb is a (by comparison) small EGT transient. Most engine folks would say "be my guest" re max climb thrust.
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It takes longer to get to the point where the change is made to climb thrust, say 1500 feet. So the engine is getting a lower temp application but for a longer period. Which is worse? The higher temp or the lower temp for a longer period?
In some takeoffs I did I found that I was actually at climb thrust, so there was no reduction to make. I don't remember if the assumed temp takeoff thrust calculation took climb thrust into account.
In some takeoffs I did I found that I was actually at climb thrust, so there was no reduction to make. I don't remember if the assumed temp takeoff thrust calculation took climb thrust into account.
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Originally Posted by boofhead
I don't remember if the assumed temp takeoff thrust calculation took climb thrust into account.
Originally Posted by boofhead
It takes longer to get to the point where the change is made to climb thrust, say 1500 feet. So the engine is getting a lower temp application but for a longer period. Which is worse? The higher temp or the lower temp for a longer period?
Originally Posted by boofhead
And that always gets me back to the argument about flap. Using Flap 10, say in a B744 instead of flap 20, gets the airplane off the ground and up to the point at which climb thrust can be set in a shorter time. This would lead to less engine wear, but most airlines will not even consider it.
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I once worked on an engine that had a time/temperature recorder. It was like an odometer that worked like a variable-speed clock. When the engine ran at a stable EGT, the "clock" accumulated counts at a fixed rate. Increase the EGT 20C, and the clock runs twice as fast; decrease 20C, and it runs at half speed.
So, the counts accumulated are representative of the turbine life consumed.
BTW, the pilots hated the gizmo, because it was a telltale of engine abuse.
So, the counts accumulated are representative of the turbine life consumed.
BTW, the pilots hated the gizmo, because it was a telltale of engine abuse.
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The automated selection of reduced climb thrust on the 737 will take assumed temperature into account, however it is user selectable to a higher climb thrust and that is what we do based on input by Boeing and CFM. That will lead to increased thrust at thrust reduction altitude in nearly all cases.
The lowest usable flap setting on the 737 is 1 and that is indeed the most often used one, however especially during winter the higher take off flap settings up to 25 are routinely used as well, depending on runway condition and obstacle situation.
Well, today that gizmo is realized in software, but it is still in use and can actually lead to reduced leasing rates and of course maintenance costs. It isn't shown to the flight crew though. And engine abuse is reduced a lot since FADEC takes care of keeping stuff within limits most of the time.
The lowest usable flap setting on the 737 is 1 and that is indeed the most often used one, however especially during winter the higher take off flap settings up to 25 are routinely used as well, depending on runway condition and obstacle situation.
Well, today that gizmo is realized in software, but it is still in use and can actually lead to reduced leasing rates and of course maintenance costs. It isn't shown to the flight crew though. And engine abuse is reduced a lot since FADEC takes care of keeping stuff within limits most of the time.
