Reduced Versus Full Takeoff Thrust

[AeroTech]

Hi,

How often (approximate percentage if possible) do you use assumed or derated takeoff thrust versus full takeoff thrust?

Feedback appreciated.

[Wizofoz]

A guess, but 85-90 percent of all takeoffs (EK 777).

Sometimes it's not much (say a 52 deg ASS TEMP on a 38 deg day), but TOGA thrust is usually only used on very heavy takeoffs (say DXB-LAX with a limiting load) or if there is a contaminated runway, or suspected windshear.

[aerobat77]

well... on the current turboprops reduced takeoffs are not approved, but on my previous bae146 time we used reduced takeoffs whenever possible, lets say 90% of the flights.

we had to perform one full thrust take off every 7 days on each aircraft for a performance check .

[TopBunk]

BA B747-400,

Note: retired 2 years ago

Reduced thrust almost every time.

The exceptions being places like Mexico City and Jo'berg, where fuel requirements and payload combined with the density altitude often required virtually full thrust (JNB maybe 1.72 EPR vs 1.74 max, but near as the same thing).

Some places (like MEX, JNB, GRU) also use an Aft C of G optimisation technique to maximise RTOW and gain payload.

Sometimes using a short runway eg Chicago, Cape Town or to avoid a delay also, but even on a long flight ex Singapore, you would normally derate somewhat to reduce from full thrust allowing 20,000+ hours on wing commonly for the engines.

[Denti]

Currently flying 737-800/700, nearly every take off (99,99%) is either reduced, derated or both.

[C212-100]

Flying A319/20/21, every take-off done in rwys in excess of 7000' are done in Flex Temperature (reduced thrust). Except if windshear reported/expected.

Regards.

[Green Guard]

when you need to walk somewhere....if you have an option to walk or run...what would you do ?

[Tu.114]

Dash 8: in summer about 80%. The few times a non-reduced T/O is needed are usually due to limiting runways, which are not uncommon in my conpany.

In winter on the other hand, approx. 60-70% of takeoffs will likely be full power: icing conditions or deicing fluid present on the aircraft are among the items excluding a reduction in T/O power.

[Dufo]

On Saab 340A, we use flex (between 92%-108% of rated power) on 99% of all takeoffs.

[kanetoads]

Are you asking Airline pilots or Corporate/charter pilots? Big difference...the 'why' is where the meat of the discussion lies.

[Desert185]

At the airline and the government, DC-8 operator: Whenever not runway/climb limited, prohibited by environmental conditions or MEL/CDL.

[galaxy flyer]

USAF: heavy airlift, probably 70% of the take-offs were reduced, but the C-5 would require full thrust at many weights.

Corporate: about 50% or so in the Global, could be more if we put emphasis on using reduced power.

Reduced is the way to go probably 90'% or more: better margins, less wear, less likely to have a failure.

GF

[lederhosen]

We do it nearly all the time and since the advent of laptop performance calculations it can look pretty strange. I remember the tower asking us if we had had an engine failure the first time we used the laptop assumed temperature on a 4000 meter runway. Low visibility is another time we do not use it.

[captjns]

I use reduced thrust every time unless limited by company procedures and judgement based on prevailing conditions or situations.

[KAG]

Basically everytimes (B737NG).

[B737NG]

Assumed temp. is used in most cases. Even in outside 36-40 Degrees Cent. we can still use 44 or 46 Degrees to cut the peak.

With the monitoring ability of Engine datas and maintenance from today the "standing time" of engines is increased significant the last 20 Years.

Whenever needed due to RWY, equipment failure or anything else: Full Thrust is used. Also once in 30 days was a proceedure I remember from a prevoius Employer.

Fly safe and land happy

NG

[mutt]

On the 787, we are expected to achieve and average 22.5% thrust reduction to avail of the most advantageous engine guarantees.

Mutt

[stilton]

You are flying the 787 ?

[kanetoads]

'Engine Guarantees'....gotta love that term. Was that coined by the blind mechanic with the blurry boroscope who's job it is to keep the engines up in the air? Tell me Mutt...how does he check if a there is bearing wear? Is there a special radar machine for that?

[FS-chick]

B737 classic/NG. Assumed temp reduced about 80% on the -300 and assumed/derated about 95% on the -800

[barit1]

kanetoads -

You don't know a lot about engine condition monitoring, do you? :p

[AeroTech]

Thank you for your feedback.

well... on the current turboprops reduced takeoffs are not approved, but on my previous bae146 time we used reduced takeoffs whenever possible, lets say 90% of the flights.
Aerobat77, why on the (or your) current turboprops reduced takeoffs are not approved?

Some places (like MEX, JNB, GRU) also use an Aft C of G optimisation technique to maximise RTOW and gain payload.
TopBunk, can you please tell me about this optimisation technique?

Are you asking Airline pilots or Corporate/charter pilots? Big difference...the 'why' is where the meat of the discussion lies.
kanetoads, I am asking all pilots who use reduced and full takeoff thrust.

A reduced takeoff thrust may increase the airplane-to-ground noise level as result of a lower flight path.
If certain airports have some noise restrictions, do you use reduced takeoff thrust or full takeoff thrust?

Feedback appreciated.

[kanetoads]

Aero - Corporate for the most part doesn't use reduced take off power because there is no incentive to do so. We can't extend engine overhaul times, as they are set. In the few exceptions where trend monitoring is allowed to extend overhaul times, we run into cycle limitations..so the overhaul expense might be delayed, but we just pay more when we get there, as more cycle limited components are coming due. All that said...only the robots are burning up more runway then they have to and putting their lives at risk by doing so. You can take the cheapest boss on earth and if given the hypothetical option of stretching overhaul times with trend monitoring..he will quickly tire of the the pilots burning up pavement and throwing up the gear at the end of the runway day after day.

[mutt]

This is like ground hog day, welcome back SSG.... btw when you start flying BIG corporate aircraft you will discover that they use REDUCED THRUST.

Aerotech... I believe Topbunk is talking about alternate forward center of gravity, have a look at this...Alternate Forward CG [Archive] - PPRuNe Forums (http://www.pprune.org/archive/index.php/t-280751.html)

Mutt

[kanetoads]

Well Mutt, It's the same thing, over and over...I come here and see you saying the same thing over and over, with not so much as an inkling as to knowing what your talking about....it's actually kinda sad. How many threads have we gone over with you basically being exposed for not having the information and evidence of what your talking about? So I come here and expose the posers once in a while. Deal with it. When you and John, and the others are willing to have a conversation, and actually finish the conversation on flex, airline hiring practices, why airlines will run an engine out to 30,000 hours etc....then I will be gone. Your avoidance is akin to cock roaches running under the fridge when the lights go on.

[TopBunk]

Aerotech... I believe Topbunk is talking about alternate forward center of gravity, have a look at this...Alternate Forward CG [Archive] - PPRuNe Forums

Mutt, exactly, thanks.

[C212-100]

knateroads,

Assuming (as you did) that reduced thrust take-off endagers operation and reduces safety says a lot about what you know about medium jet engines.

Do yourself a favour and instruct yourself by reading something about this subject.

Regards.

[kanetoads]

Typical on this forum that the only defense to any supposition that I make is that a- they are an aviation expert b- that they are in position to 'school me' in aviation. You guys are going to have to step way, way up to the plate in order to even consider getting up to my level of aviation experience. Bottom line, reducing available runway ahead of you on purpose increases the risk on departure...and for what reason? Because your chief pilot wants to run those engines out as far as he can, because corporate sold him on the idea that the airline will go bust if they spend one penny more then they have to.. Reminds of Delta taking peanuts and pillows off the flight as a cost cutting measure. Certainly this is spoon fed to the pilots who have no clue as to aircraft operational costs, and is just a technique to get the unions to take concessions in pay and what have you. If you got hired under the premise that you can't think independently, nor rock the boat with any ideas that might actually improve things...it's laughable that your going to come here and try to sell others on your expert status in aviation. Your paid not to think, stick with what your good at.

[Lord Spandex Masher]

I take it that you never operate in temperatures greater than that which your engines are flat rated to?

[cheemsaf]

We keep it simple. 100% power or 100% power with afterburner. When more than 50% of runway length will be used to rotate, and/or when start-stop distance is longer than the runway (all things considered, DA, RCR, terrain, etc): we light the afterburner - dramatically reducing the distance numbers. Some exceptions apply if cables are in place with shorter runways (less than 8K). F16

@kanetoads : Why do we put runway behind us? Non-AB takeoffs dramatically increases our ASD, with more available valuable training being met with more gas in the tanks. I'm not defending putting runway behind you 100% of the time; but when you can mitigate it with safety features outweighing the risks with added benefits: then by all means.

& you should seriously check your ego buddy: "to your level of experience"?? Really? I'm pretty sure there are a lot of people on this forum with plenty of more experience than you and I. And don't quote flight time to me. Experience is measured in events, not hours. Pilots with experience know this.

[barit1]

kanetoads:

The airline operates in a competitive environment, and costs are a big concern. The aircraft are - in general - quite overpowered for the operating environment (runway length, density altitude, etc.). Operating efficiently means - among many other things - using flexible thrust to meet OEI requirements, but not a lot more.

If you think doing this and keeping the extremely reliable engine on wing 20k-30k hours somehow compromises safety, you are really out of the loop. I would not be surprised if airline engine reliability (IFSD rate) is an order of magnitude better than your bizjet engine, simply because the experience database is far greater, and the airlines demand this reliability.

[The African Dude]

Bottom line, reducing available runway ahead of you on purpose increases the risk on departure...

The V1 is worked out to enable a stop before the runway end. No person in their right mind stops after V1 so the end result is the same. Reduced thrust takeoff, before V1 you are not putting your life at risk. However, you are saving engine life which means you are less likely to have an engine failure elsewhere. I am sure that that is the REAL "bottom line".

AD

[kanetoads]

Barit - Profits over Safety. Plenty of operators don't use Flex, Reduced power, etc... Cheemsaf - Thanks for making my point. When you do come up with a reason to for putting more runway behind youf or safety reasons I am all ears. African - Your assumption that as long as you have balanced field..is just using the 'good enough' mentality toward mitigation of risk, and only operates in the world of the airlines where if they can get away with it, then 'good enough'. Imagine if the Feds didn't require you to have balanced field...what then?

[grounded27]

WOW this has turned into a long winded topic. Bottom line is that reduced thrust T/O is normal operation unless the full thrust is needed as a result of many variables. Is there any serious question to this answer!

[mutt]

Imagine if the Feds didn't require you to have balanced field...what then? Actually we are not required to use balanced field performance by the Feds, I presume that you have heard about optimized V-speeds, or Min V1, or Max V1, or Improved Climb, or Overspeed?

As for Cheemsaf "making your point", didn't you realize that he was talking about a F16 Fighting Falcon, as there aren't any airline/corporate aircraft with afterburners (Since demise of Concorde :{:{)

I take it that you wont ever fly again in an airliner as we are too dangerous :):)

Mutt

[OverRun]

kanetoads,

This part of PPRUNE operates in a collegial fashion and is usually conducted with some decorum. I rather think you owe Mutt and others an apology.

OverRun

[rubik101]

an analogy: when kanetoads sets off in his car, he floors the accelerator, lays rubber and makes smoke, achieving his top speed within a few seconds of brakes release.
I prefer to gently accelerate, saving wear and tear on my engine and keeping the passengers happy with my smooth acceleration to my moderate cruising speed.
Unless we are at Santa Pod or some similar drag strip in the US, who would you rather sit beside?
My main concern though, would be the wear on my engine, which will eventually affect the performance and reliability. One day, I might need all the power I can get. It is nice to know that my engine is not worn out or close to expiration.
btw, I too have 40 yrs of flying experience and used flex/derate/reduced on almost every take-off for the last 25 or so.

[ross_M]

Assumed temperatures seem quite a hack to indirectly fooling the engine into lower power. Are there maufacturers that just allow the flight crew to enter a percent of rated / calculated power? Seems a bit safer as a philosophy.

[stilton]

I sincerely hope that Kt is not in command of anything more complex than an out board motor.

[Shiny side down]

Assumed temperatures seem quite a hack to indirectly fooling the engine into lower power.

It is not a hack.
Airbus, Boeing, etc, use defined methods and procedures. The process is incorporated into the management systems.

In using reduced thrust, you are using the engine performance that would be available from those engines in a higher ambient temperature (ie not as much oomph), to lift the mass that would be possible in the higher ambient conditions. However, you are still in your own ambient conditions.
Net result- overall wear rates on the engines are reduced.

And if in doubt. Don't select it.

Are there maufacturers that just allow the flight crew to enter a percent of rated / calculated power? Seems a bit safer as a philosophy.

Yes. In some machines. It is a derate. And a slightly different set of circumstances. On the B737NG, it was selectable. ie a 27K engine could be operated at 24K (I cannot remember the full figures)

On several aircraft I flew once, this allowed an intermix of rated engines. ie a 22K engine, with a 24K engine on the same airframe.
But this is not intended as a per-flight, selectable value. They are treated as separate procedures.

ps. open to correction of my poor explanation....:rolleyes:

[de facto]

Since when the Feds require a balanced field?:suspect:
I think the gentleman is confused...
Do you mean balanced v1(since you dont use assume temp)?

[TakeTheHighRoad]

Thread ender - So does anyone use reduced thrust without the financial incentive of extending engine overhaul times, ergo for the express and sole purpose of 'enhancing safety by putting less stress on the engines'? Aside from a few pilots I have known that don't push the engines up at alt during cruise, I haven't seen nor hear of it.

[galaxy flyer]

Having read SSG V1 thru V9 before, I'm a consciousness objector for this thread. As is, I think, another well-known denizen of this forum.

GF

[barit1]

There is a simple economic reason for kt's point of view.

In an airline operation, engine maintenance cost is a very significant part of the corporation's total cost structure, and so flex thrust makes much sense. Costs make the difference between profitability and bankruptcy.

In kt's world, the engine maintenance cost (in fact the whole bizjet operation) is a very small part of the corporation's total cost. If engine maintenance cost were zero, or if it were tripled, wouldn't make a pfennig difference in the corporation's EPS. :rolleyes:

[cheemsaf]

Mutt: Not at all...though some of the things we do I question. Although the thought always does cross my mind when I don't have a parachute strapped to me & I'm not sitting in the cockpit - I hope these guys are on top of their game. I have seen it once (only once) where they weren't. I was sitting by the wing and the flaps started to extend after the power was pushed up for takeoff. Scary...:eek:

I guess at that point, this whole derated/reduced thrust topic goes out the window

[barit1]

TakeTheHighRoad:

I know of one engine OEM that very pointedly says that derate/flex has no effect on safety, but is strictly an economic issue. I think this is the general industry attitude, although some crews believe safety (failure rate) is enhanced with reduced thrust.

There is another point to be made: Flex thrust results in operating at a more constant thrust/weight ratio. This may be trivial or not. It means that the TO roll time to V1 & Vr is more constant, and the pace of cockpit activity isn't hurried one day and leisurely the next. Maybe the human factors crew can comment.

[TakeTheHighRoad]

Barit - If I was allowed to overhaul on condition, you could bet i would do everything to not only get the overhaul cost down, but not have to go through it all all. Having done my share of overhauls, hot sections, and a back and forth with the factory over a bearing failure...it's a pain...really is. But I am just not sure how much grass at the end of the runway I would want to just fly over to put another dollar in the boss's pocket.

[barit1]

Are you saying your airplane won't perform OEI like the AFM says it should? Are you saying bearing failures are a big issue on your engine? :eek:

I note that loss of thrust on one is not an emergency in an airliner AFM. And further, engine reliability is such that the typical airline pilot would statistically fly two or three careers before encountering an engine failure during takeoff segment.

[TakeTheHighRoad]

Barit - I'm just joking. If corporate made us use reduced thrust to save a buck, it would be pretty funny..guys would probably just be pulling it off at the end.... As far as engine failures go, I've had 4 so far...personally I think it's inevitable that a pilot that flies enough is going to see some malfunctions, all over the plane. Maybe it's because I deal directly with the owners...it just seems comical to consider departing farther down the runway, so that we can make the guy a little richer.

[barit1]

I think you've just made my case - see post #44.

[grounded27]

By personal experience, Your CO. is ACMI, your Aircrft and Engines are leased. As a result, your customer rarely fills your aircraft to less than MGW and by personal experience rounds down the numbers. That was a different life that resulted in many full thrust T/O's

[kanetoads]

Well at issue really...is to separate those that have actually gone through the overhaul process vs those who believe what they are told, then run around and regurgitate as gospel.

But I suspect the same people who will argue for reduced power departures are the sames ones who bought it hook line and sinker that taking pillows and peanuts off of Delta flights was what was REALLY needed to save the airline.

If you haven't seen the numbers first hand, spent the money, actually been in charge of this stuff, then your simply going by what your chief pilot/department manager is telling you...

Anyone know what the actual fuel cost is, how about insurance, what about the gate fees, how about the real cost of the aircraft...

It's a tough sell to convince me that your company is going under with out the use of Flex when you just bought 20 new A300s. Just sayin.

[bubbers44]

Using max take off power costs your company money. If you don't need it why waste your companies resources?

[barit1]

kt:

It's a tough sell to convince me that your company is going under with out the use of Flex when you just bought 20 new A300s. Just sayin.

Bought a new CFM hot section lately?

(PS - Where would I go to buy "20 new A300s"? Do they still make them?)

[Denti]

No, they dont, but you can buy refurbished A300-freighters from EADS.

There are big differences between airline and GA business models. A shorthaul aircraft in the airline business needs to fly around 3500 hours a year to earn its keep, a longhaul aircraft around 6000 hours a year. Most GA aircraft do not more than 500 hours a year and many do less. Reliability is a key factor for airlines as they cannot spare extra ground time without schedule problems, therefore high reliability is one of the main selling points of airline aircraft. GA aircraft have a lot more ground time which can be used for maintenance and usually do not reach the same reliability numbers as airline aircraft which isn't really a problem after all with all that much spare ground time.

That said most airlines pamper their engines. For example we wash engines around every other week during scheduled maintenance, of course continous monitoring is absolutely standard with downlinking engine parameters from every few minutes to several times an hour via ACARS/datalink and rigorous maintenance action. As changing an engine is often times faster (around 6 hours for a PW4000) than doing extensive maintenance on the wing we are not against taking them off, however a complete overhaul is a rare thing, it is usually just a parts change. That requires several spare engines of course, but again, that is standard airline operation anyway.

And of course reduced thrust when you do not need full thrust is another measure to increase engine life and at the same time reduce maintenance cost. If full thrust is needed we use it of course, that is why we bought it in the first place. We do use full climb thrust now wherever usefull (doesn't really help with a low level off altitude like london area departures) to save on fuel, so reduced thrust is only used for take offs up to 1000ft AGL. Of course that means nearly every time that climb thrust "reduction" is actually an increase in thrust.

[barit1]

Of course that means nearly every time that climb thrust "reduction" is actually an increase in thrust.

This is cognitive dissonance to many pilots, but from an engine standpoint, it's perfectly fine, even desirable; the takeoff segment serves as a "warmup" for the more demanding climb. :)

[TakeTheHighRoad]

Ok, then it follows that iif you guys pull it back for the two minutes that you could go max thrust...then I will assume that for the other 20000 hours at altitude, your pulling back the power from max cruise as well... Right? ;)

[barit1]

In ships I'm familiar with, you won't reach Max Cruise until well above optimum altitude / normal Mo.

[TakeTheHighRoad]

Well, see Barit, that's where your argument comes undone.

Keeping costs down in a flight operation is a matter of containing costs in a number of areas...

So pulling back on the power for departure might extend engine overhaul times, but flying around at altitudes not optimal for the trip burns more fuel right now...we could go into insurance, training costs...and for me...pointless..

Reminds of when the ex CEO of United blew 100 million on non refundable aircraft orders and almost bankrupted the company...

I won't argue that power reduction can save overhaul costs, but chances are, that procedure in an organization that is probably bleeding money in other areas is like the kid who put his finger in the dam.

Feel free to fly it to fence if you want, but unless I was convinced that the rest of the organization was as motivated in their efforts to save money, I wouldn't put any more runway behind me then necessary.

[galaxy flyer]

TTHR

You do relealize that at Max Cruise Thrust, the engine is at considerably lower thrust levels than at Take-off Thrust?

GF

[TakeTheHighRoad]

Galaxy -

I've done my share of engine overhauls and hot sections...I'll bet you $100 you can't find one guy on Earth who's going to prove that reduced thrust departures (for two minutes) is gong to save more in engine overhaul costs then say 5000 hours of running at max cruise thrust at altitude.

I might also add that more time on the runway, gives the plane more of a chance to pick up FOD...food for thought considering the Concord was over gross...she might have missed that chunk of metal if she had been lighter...

[mutt]

So SSG reincarnation number 10 has finally admitted.....

I won't argue that power reduction can save overhaul costs

But his problem is with management?

Time for his future rants to be in the Airlines, Airports and Routes forum :):)

Mutt

[kanetoads]

Mutt...there is no question that the sum total of your aviation repertoire would fall flat in a person to person debate with me. It would be a slaughter.

Do I argue that pulling back the power to 50% all day long would extend engine life...no...nor would sweeping the runway prior to all departures, or flying only in land, never near the ocean, staying away from the desert, or ice, that could crack off the inlets and dent a blade...or also keeping the 200 hour pilots you hire off the throttles so as not to overspeed inadvertently...we could also start doing oil changes after every flight...

And in the end, it's some mechanic, probably the same guy that missed the jack screw at Alaska Airlines that is checking the blades...

All right Mutt...do you get it? Do you actually fly planes to understand what I am talking about?

So there you are lined up on the runway, pulling it off as far down the runway as possible on some misguided mission to save the company money, when in fact there are a hundred other ways to do so that won't compromise safety one iota.

Seriously Mutt, just shut up..your just too stupid to talk.

[FE Hoppy]

@kanetoads
You may wish to lay off the skydrol cocktails mate!

[Brian Abraham]

Mutt...there is no question that the sum total of your aviation repertoire would fall flat in a person to person debate with me. It would be a slaughter. So says a person who's only association with aviation is as a pax in 46C. :ugh: Worked out that rotor rotation thingy yet? :cool:

[mutt]

person to person debate with me You can find me at the Dubai Airshow next week, either at the Boeing or Gulfstream chalets, come over and chat, we will have immediate access to representatives who can validate your "concepts" of large aircraft operations.......:ok::ok:

Mutt

[rudderrudderrat]

@ TakeTheHighRoad.

If you looked at any metallurgical paper such as DoITPoMS - TLP Library Creep Deformation of Metals - Effects of stress and temperature (http://www.doitpoms.ac.uk/tlplib/creep/stress.php), you'd see that the creep rate of a turbine blade will have an exponential dependence on temperature.

It pays to run the engines as cool as possible with any power setting greater than MCT.

[TakeTheHighRoad]

I think that's probably enough. JT

[mutt]

So true to form, once you are exposed as having no technical knowledge of large aircraft performance or operations, you immediately turn to insults.... usually resulting in a forum ban........

I wonder who you will come back as next time :{:{:{

Mutt

[Brian Abraham]

TakeTheHighRoad aka SSG, take a hike tosser, mutt is a highly accomplished aviator, along with many others you take exception to - galaxy flyer, con-pilot etc. You have proven time and time again under your many guises that you know absolutely zip when it comes to aviation, and have absolutely nothing substantive to contribute to discussions.

Figured out that rotor direction thingy yet?

[enicalyth]

Brian

Well said. By the way you don't still have a copy of my RR Merlin spreadsheet do you? Mislaid mine.

[kanetoads]

Well at the end of the day the real justification is that you guys do what your told...it just makes you guys feel better when pulling the gear up over the fence that you have 'just cause'.

It's the same mentality of a guy that sits down and eats three cheesecakes, obviously overweight...tells everyone he's got a thyroid problem.

[barit1]

Problem? Who has a problem?

I think it's just fine that you run rated thrust on every takeoff, because that's more spare parts revenue for my employer (from whom I've retired, but I still collect dividends from). That's easy money for us. :)

Just don't think that attitude will find traction in an industry that survives or perishes on its avoidable costs.

[Old Smokey]

barit1,

You had me worried for a moment, until I did a re-read of your tounge in cheek remark, which, to me, ends this whole discussion. If an engine manufacturer just loves full thrust takeoffs in the name of increased revenue for them from spare parts sales, that says it all:ok:

Doubters should take a good look at an Engine stress Vs Engine life graph which pretty much says it all, reduce the thrust (if possible), and increase the engine life and likelyhood of Engine failure DRAMATICALLY. I don't have the facility to post diagrams, but will have it done by a fellow prooner (my son). That one diagram is worth a thousand words.

TakeTheHighRoad, SSG, and all of your other mutant offspring, It seems that you have taken issue with one of the regular contributors here, who is part of the back-bone of PPRune. May I refer you to a contributor who:-

(1) Has an incredibly long career as a Professional Pilot and Performance Engineer for a MAJOR airline,

(2) Has vast experience on small to VERY large aircraft in that, and other airlines,

(3) Receives Boeing and engine manufacturer data directly from them, and returns it if faulty, which these major manufacturers accept,

(4) Very gracefully accepts correction if he makes an extremely rare mistake,

(5) Is an absolute gentleman of unparalleled restraint when insulted by FOOLS. He obviously belongs to the school of thought that if an insult is given, but not accepted, the insult remains with the person initiating it.

I have learned a lot from his sharing his considerable experience.

He goes by the name of Mutt on these forums:ok:

On a personal take, most discussion regarding use of Flex/Reduced thrust centres on cost saving. It's a very valid and truthful point, but, even if it were not, I would (and do) use Flex/Reduced thrust for every Takeoff possible in the interests of safety, such safety enhancement emanating from very significantly reduced engine stress, thus leading to a very significantly reduced probability of engine failure:ok:

This was an otherwise good thread for all pilots. Unfortunately it has been soiled by you, TakeTheHighRoad, SSG, and all of your other mutant offspring. Do us all a favour and ... or, as my good colleague Jack Macdonald once observed to me many decades ago .. in respect of a court martial in which he was a material witness .. "He said 'Go away, or words to that effect, Sir". (I have to play with extreme even-handedness) - JT

Now, let the sane debate continue.........

Best Regards,

Old Smokey (who does not share Mutt's degree of restraint.:)

[barit1]

Old Smokey:

Well, I didn't intend my post tongue-in-cheek - I was perfectly serious. It's only a few pfennigs in my pocket, but it somehow feels better when it's coming from hot jock like kt. :E

[BlankChecks]

What I would like to know is how the airlines can run their cycle limited components to 4 and 5 times the component cycles of GA Jet Engines.

[galaxy flyer]

Here it is....SSG V10. :=


For one thing, GA engines are not designed for the use airline engines are, think of it, how mang GA engines will see 16,000 hours?

GF

[BlankChecks]

Galaxy, I am all ears to how you and experts are going to demonstrate that an inner turbine wheel on a JT15D is some how manufactured to a lower standard then say your typical airline engine.

That's good to know though...the next time I do an engine overhaul I can now can call up Garret, Pratt, or Rolls and say...

'You know I heard on the internet that I can get a turbine wheel that will go 20000 cycles instead of the 5000 cycle one your trying to sell me'. and the response will be..

'Oh, yeah, that's the extra super duper turbine wheel that we only sell to the airlines, would you like one?

[Brian Abraham]

how you and experts are going to demonstrate that an inner turbine wheel on a JT15D is some how manufactured to a lower standard then say your typical airline engine.Could it be that the designers fashion an engine to meet the expected usage pattern - metallurgy (single crystal blades), plasma coating blades with exotic materials, cooling (plasma drilling passages, casting blades with passages), active blade clearance. Technology costs money, and the usage pattern of JT15 powered aircraft was probably designed with 500 hours per annum in mind. Calendar time likely to come up before hours or cycles. Could it be? Nah, not a chance.

Formula One guys should buy their tyres at Harrys Cheap Tyres, they do the same job, both just bits of rubber on a wheel.

[BlankChecks]

Brian, we could speculate all day long that airline engines have more unobtanium in them then GA jet engines.

But I think those in the know here, are very well aware that the answer to this question lies in two turbine wheels made to spec...and one operator gets to do 'this' and another operator gets to do 'that'.

[Mad (Flt) Scientist]

Well, here's one example.

The stress in a highly heated part of the rotated machinery in a gas turbine is highly dependent on the temperature of operation, especially the peak temperature. Such that a change in operating temperature of only a few tens of degrees can commonly double or half the effective fatigue life of the component.

the parts are not manufactured to different standards; they are USED to different standards.

Military fast jets are not manufactured to lower standards than civil airliners. yet hardly any military aircraft manufactured in the 70s is fit for continued operation without substantial rework - think of all the rewinging programmes the military routinely conducts to extend the service life of older aircraft. When was the last time you heard of a civil aircraft being re-winged? They dont need to it, because they are "babied" compared to their military brethren - one aircraft flies at a sedate 0.8'g' to 1.5'g', the other between -1'g' and +6'g' perhaps.

[barit1]

It's all dollars and cents.

To design to an airline-standard cycle life (more specifically, Low Cycle Fatigue or LCF) a part will likely be heavier, use higher grade materials, have a more expensive manufacturing process, and/or more stringent inspection. This all adds to the cost.

Applying all these goodies on a bizjet engine that only flies 500 hours/year and which may become obsolete before it wears out, becomes a pointless exercise; and might drive the engine cost to uncompetitive levels.

In short, it can be done, but what's the point?

[mutt]

Blank Check, SSG, Kanetoads, whatevernext

I suggest you download the following presentation and educate yourself before your next posting on this subject.

SmartCockpit - Airline training guides, Aviation, Operations, Safety (http://www.smartcockpit.com/pdf/flightops/aerodynamics/30)

In fact, there are quite a number of presentations on the smartcockpit website that would be beneficial to you :):)

Mutt

[BlankChecks]

Mad - The only differentiation in 'USE' between airlines and GA jets would be reduced thrust departures and possibly a more vigorous inspection program.

So I'll give it to you that an airline submits an operating - maintenance program that helps the engine manufacturer feel more comfortable about allowing longer cycle limits. I am just curious what information the engine guys are crunching.

It's not hard to figure out that an airliner can push the engines out as far as the mechanic with a boroscope will allow based on visible evidence of damage, etc.

At issue are components like bearings, that can't be inspected, that are just allowed to run out say 4-5 times farther on an airliner, based on what?

I see it like this. Obviously the manufacturer doesn't want broken parts bringing down planes, but at the same time the airlines won't accept 3500 engine overhauls due to the obvious cost. I surmise that the engine manufacturers are being really conservative with corporate jets. (Greed)

So what's fair is fair, if the airlines can run their engines out until the mechanics see a problem, corporate should to. In fact I might talk to my local FSDO about this.

[Junkflyer]

Our airline uses reduced thrust whenever possible. The program reduces the available takeoff distance by 1,000 feet to add some fudge factor when factoring the numbers.

[barit1]

The program reduces the available takeoff distance by 1,000 feet to add some fudge factor when factoring the numbers.

Nice touch of conservatism, and I won't argue with it, as long as it produces the average fleet % reduction per the OEM's warranty.

But there's conservatism already built into the assumed temperature (flex) method, in that engine thrust is set per the flex temp, but the airplane wing is flying in the real OAT. So performance is better than book @ the real hot day condition.

[FE Hoppy]

BlankChecks,
Have you stopped to wonder why you are a lone voice on this subject? There are many tens if not hundreds of thousands of flying hours experience on the thread let alone site, who from experience know the theory to work in practice. Supported by evidence from the manufacturers and a big thumbs up from the shareholders and the passengers who fly in ever increasing numbers. Failure rates continue to fall as do operating costs, so please please tell me why you can't see the benefits?

[galaxy flyer]

SSG in all your various guises,

You do know that a number, increasing at that, of corporate engines are "on condition" including the CF-34 (CL-600 series), HT 7000 (CL 300), BR 710 (GLEX, GLF) to name a few. The HT 7000 is hugely derated. The BR 710 offers flex power take-offs thru the FMS.

Please stop extrapolating from one data point--the aging JT-15D. You are making the pros flying newer business planes look like an uneducated group of Neanderthals. Just saying'

GF

[barit1]

SSG et al. brings up an interesting point, namely bearings. He seems to be aware of a bearing life issue that's outside my limited (45 years) experience.

Bearings and lube systems on our engines have generally been very reliable; I can only recall one bearing on one engine type that required special attention, and it is no longer a worry item after the type achieved maturity.

Who else finds bearing life or reliability a significant worry?

[Comeonseriouslynow]

You normally run to a few posts ? Why ever the change in MO ? JT

[galaxy flyer]

Another first time by SSG Version 11!, will we see another?

First, it is "you're", not your. It is a contraction, not the possessive.

Second, I am proud to be associated with Pprune members, such as mutt, Brian and FEHoppy. Can we add Old Smokey, if so, I am humbled?

Third, which way does the rotor thingy go?

Fourth, barit1, the only bearing failure I have heard of, as a design failure was of a military jet. A friend, tech rep and bearing engineer at the manufacturer and ANG pilot, was handed a handful of obviously broken parts, reported to be a main bearing. Asked what the original bearing looked like and a set of drawings, was told that he didn't have a clearance to see them. "Then, he replied, it broke.". j58, btw.

GF

[Brian Abraham]

The GE 90 includes 26 life-limited rotating parts and three stator parts. The lowest limit is found on the HPT with a 3,500 flight cycle limit, while the highest is 30,000 cycles. One part in the HPT has a life of 3,500EFC, another 9,500EFC and others 15,000EFC. Other engine parts, such as the HPC, have lives of 9,800EFC, 10,000EFC and 11,000EFC. The list price for a full shipset of LLPs is $8.07m.

Life limits are defined by the engine’s operational thrust rating and operators must ensure the life used is properly tracked.

The average GE90-94B time on-wing for first run is 16,000-18,000FH. Considering the limiting LLP life is 3,500 cycles, engines operated at the lower ratio will have to be removed to replace this part, while long-range engines will not be affected and are removed for performance deterioration. Once removed, the motor will typically need a core performance restoration — i.e. high pressure compressor and combustion chamber modules will need refurbishing and the high pressure turbine will need overhauling in order to replace the limiting HPT interstage seal.

Once the engine has had a first shop visit, it should have enough performances to remain on-wing for 13,000-16,000FH when operating at a flight ratio of six. At the time of removal, an overhaul will be necessary. The total hours and cycles accumulated will be 29,000-34,000EFH and 4,000-5,700EFC; consequently the replacement of LLP will have to be carefully evaluated considering the expected on-wing time following the repair.
For some airlines, operating the engines at a ratio of two and with engines reaching an interval of 14,500EFH and 7,300EFC, a few LLPs will have to be replaced.

The interval post overhaul is usually equivalent to the first run (16,500 - 17,500EFH and 4,000 - 4,400EFC for operations at 4.0EFH per EFC and 18,500 - 20,000EFH and 2,300 - 2,500EFC for operations at 8.0EFH per EFC). It should be noted that GE has now introduced a new HPT seal with higher life limit; therefore the 3,500 limit will no longer be present.

The GE90-115B engine is still in the ‘young phase’ and removals have been few. This is mainly for technical issues and not for performance restoration, making available information limited. Since the engine is used in ultra-long flights, cycles are limited. The expected EGT margin of new engines is in the range of 40°C for the -115B and 60 Deg C for the -110B version. Based on the experience accumulated on the “smaller” engine model and on on-wing performances, the manufacturer and operators are expecting a first run of between 2,000 and 20,000 flight hours. Similar to the smaller version, a performance restoration will be necessary to restore serviceability and achieve a second run of 15,000-17,000FH, with the limiting factor being most probably the HPT interstage seal. An overhaul type of shop visit will allow the engine to be on-wing for a time similar to the first engine run.

SGI’s experience is a first shop visit costing in the region of $4m. The second shop visit will be both more extensive and more expensive, in the range of $5m. Shop visits are highly dependent upon engine thrust, utilisation, environment and engine standard. Considering the two shop visits costs and the intervals indicated, cost of the engine is between $252 and $310 per hour.

The average utilisation hours/cycles ratio is 5.4. China Southern and Saudia use the GE90-powered on medium-haul services at FC times of 2.5-4.0FH. Air France, Austrian, British Airways, Continental and KLM use the aircraft on long-haul services at FC times of 6.5-9.5FH.

Because of the newer and long range aircraft application, the 115B version has a much higher average ratio (7.1) and accumulated 3 million FH and half a million flight cycles. The 110B1 version with Air India is usually operated at a ratio of 11-13.

The above from a GE handout.

According to Gulfstream, by way of comparison, the GV, which is a long range business jet capable of 14 hour legs, has a ratio of 2.2 hours.

Since your favourite is the Citation, I checked the usage pattern of one model, among the many available, and CESCOM reports an average annual utilisation of 275 hours and the average trip length 435 miles. The Encore had a trip length of 393 miles.

Vast difference between airline and business jet.

It will be noted in the above that an airline engine may be removed for rectification, not because it has reached an hour or cycle limit, but because fuel burn has become excessive. Having to off load pax or freight in order to load extra fuel for a hungry engine at some point becomes self defeating economically.