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777 With De-rated Engines  
User currently offlineembrider From United States of America, joined Mar 2010, 26 posts, RR: 0
Posted (2 years 4 months 4 weeks 1 day 4 hours ago) and read 5971 times:

I was reading about SIA in Wikipedia and learned that all their 777-200 (and they have quite a few of them) are 777-200ER with de-rated engines. What exactaly are "de-rated" engines? Why would an airline choose it over a "regular" engine? What are the real differences between SIA -200 and the other -200s in terms of performance, etc?

23 replies: All unread, jump to last
 
User currently offlinefpetrutiu From United States of America, joined Aug 2007, 866 posts, RR: 0
Reply 1, posted (2 years 4 months 4 weeks 1 day 4 hours ago) and read 5943 times:

Fuel consumption, those are mostly operated on short hauls and long runways. No need for the higher thrust ratings.

User currently offlineViscount724 From Switzerland, joined Oct 2006, 24075 posts, RR: 22
Reply 2, posted (2 years 4 months 4 weeks 1 day 4 hours ago) and read 5943 times:

Quoting embrider (Thread starter):
Why would an airline choose it over a "regular" engine? What are the real differences between SIA -200 and the other -200s in terms of performance, etc?

Probably so the aircraft can be certified at lower maximum takeoff weights which reduces landing fees which are normally based on MTOW. From what I've read, the differences mainly involve paperwork.


User currently offlineembrider From United States of America, joined Mar 2010, 26 posts, RR: 0
Reply 3, posted (2 years 4 months 4 weeks 1 day 4 hours ago) and read 5917 times:

Quoting fpetrutiu (Reply 1):
Fuel consumption, those are mostly operated on short hauls and long runways. No need for the higher thrust ratings

Thanks. It makes sense but wouldn't you have the same effect with "regular" engines, just applying less trust? You would still have a more capable aircraft if you ever need to deploy it on another route


User currently offlinejkudall From United States of America, joined Mar 2004, 615 posts, RR: 1
Reply 4, posted (2 years 4 months 4 weeks 1 day 4 hours ago) and read 5862 times:

Quoting embrider (Reply 3):
Thanks. It makes sense but wouldn't you have the same effect with "regular" engines, just applying less trust? You would still have a more capable aircraft if you ever need to deploy it on another route

To be more clear, typically de-rating is essentially what you describe, at least during the takeoff phase of flight. If runway/airport conditions allow a de-rated takeoff, then the pilots select the appropriate setting in their flight computers and the plane will use a lower thrust rating. The engines themselves are capable of the full thrust, but using the de-rate option puts less wear and tear on the engines, uses less fuel, etc.


User currently offlineQF340500 From Singapore, joined Oct 2011, 160 posts, RR: 0
Reply 5, posted (2 years 4 months 4 weeks 1 day 4 hours ago) and read 5806 times:

thanks for the explanation. I was always asking myself the same question... why has SQ not bought the "normal" 200 then instead, if they dont need the power?

User currently onlineBMI727 From United States of America, joined Feb 2009, 15476 posts, RR: 26
Reply 6, posted (2 years 4 months 4 weeks 1 day 4 hours ago) and read 5749 times:

Quoting fpetrutiu (Reply 1):
Fuel consumption, those are mostly operated on short hauls and long runways. No need for the higher thrust ratings.

I don't think it is fuel consumption so much, since the only changes to the engine in most cases is the software controlling it. The benefit of derated engines is less wear and tear leading to lower maintenance costs and better on wing time.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlinefpetrutiu From United States of America, joined Aug 2007, 866 posts, RR: 0
Reply 7, posted (2 years 4 months 4 weeks 1 day 4 hours ago) and read 5728 times:

Quoting BMI727 (Reply 6):
don't think it is fuel consumption so much, since the only changes to the engine in most cases is the software controlling it. The benefit of derated engines is less wear and tear leading to lower maintenance costs and better on wing time.

It is a software change, one that limits the thrust available and you are right increases the life of the engine. But on routes this is used on, also contributes to fuel savings, particularly during take-off and cruise phase. (usually these are shorter routes where a 20kts slower cruise speed would not make a noticeable difference, except for the pocket book)


User currently offlineCX Flyboy From Hong Kong, joined Dec 1999, 6533 posts, RR: 55
Reply 8, posted (2 years 4 months 4 weeks 1 day 3 hours ago) and read 5602 times:

Also, regulations only allow a maximum derate of 25% from the maximum thrust. So if you regularly fly at lighter weighs, a 25% derate on the day might still be too much thrust. If those engines are derated (and normally given a different engine type name) then you can do 25% derate on the already re-rated engine.

CX has done this on their 777-300s which were fitted with Trent892s, each producing 92,000lbs of thrust. CX fly their 773s regionally only and have lowered the MTOW to 263tonnes. (The 777-300 is around a 300t plane). By lowering the weight to 263t, they pay lower landing fees and overflight fees, and even 263t is plenty when flying around the region. We rarely max out at that weight. Since the MTOW has been lowered, 92,000lbs of thrust was too much so RR did a software and paperwork change in the engines and re-rated them to 84,000lbs of thrust. The engines are now called Trent884Bs. Less thrust means less wear and tear and lower maintenance costs.

Keeping the engines at a higher rating and telling pilots to use less thrust will still result in the highest thrust being used at times, i.e. in turbulent and windshear conditions, and during the latter stages of the climb where maximum thrust might be used to keep the high rate of climb going even though for economic reasons it is not needed.

The Trent884B rating I believe is unique to CX where the engine produces a maximum or 84,000lbs of thrust for takeoff, but those lower thrust ratings are not good enough to keep a decent rate of climb going at higher altitudes and hence as the aircraft climbs, the maximum thrust rating slowly increases so that at higher altitudes, the full 92,000lbs of thrust is available. Without this, the 773 would be limited to lower cruise altitudes which is less than efficient. Its all juggling with costs and tweaking the variables until a lowest cost solution can be found.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 9, posted (2 years 4 months 4 weeks 1 day 3 hours ago) and read 5602 times:

Quoting fpetrutiu (Reply 1):
Fuel consumption, those are mostly operated on short hauls and long runways. No need for the higher thrust ratings.

There's not really a meaningful change in fuel consumption except during takeoff/climb...it makes no difference in cruise since you're not high enough up the thrust curve in cruise to run into the derate.

Quoting Viscount724 (Reply 2):
From what I've read, the differences mainly involve paperwork.

There's a little more to it than that, but not much. Changes to certified MTOW are purely paperwork; "permanent" derate of the engines changes out a physical programming plug on each engine computer. The plug tells the engine computer what thrust rating it should behave as.

Quoting jkudall (Reply 4):
The engines themselves are capable of the full thrust, but using the de-rate option puts less wear and tear on the engines, uses less fuel, etc.

The engine is physically capable of full thrust but, if it's a permanent derate then you can't access the higher thrusts (except in some oddball cases like the 737NG) without actually changing the engine programming plug. By far the most significant reason to do it is reduced maintenance and longer time on wing.

Quoting fpetrutiu (Reply 7):
But on routes this is used on, also contributes to fuel savings, particularly during take-off and cruise phase.

Take-off yes, cruise no. If you're cruising at M0.85 it's going to take the same fuel regardless of whether you have a full or derated engine, since the derate selection doesn't change the aircraft drag polar or physical engine components at all.

Tom.


User currently offlineUnited1 From United States of America, joined Oct 2003, 5815 posts, RR: 9
Reply 10, posted (2 years 4 months 4 weeks 1 day 3 hours ago) and read 5588 times:

Quoting QF340500 (Reply 5):
thanks for the explanation. I was always asking myself the same question... why has SQ not bought the "normal" 200 then instead, if they dont need the power?

Probably because if they ever did need the range from the aircraft their would be no way to convert them...vs the derated 200ERs are simply a paperwork exercise and software/chip update. It probably also helps with aircraft resale being able to market the 200ER vs the 200.

IIRC BA did this with some of the 744 calling them "744 Lite" and by limiting the MTOW they saved quite a bit of money in landing fees on the shorter transatlantic legs where full range wasn't needed.



Semper Fi - PowerPoint makes us stupid.
User currently offlinefpetrutiu From United States of America, joined Aug 2007, 866 posts, RR: 0
Reply 11, posted (2 years 4 months 4 weeks 1 day 3 hours ago) and read 5527 times:

Quoting tdscanuck (Reply 9):
Take-off yes, cruise no. If you're cruising at M0.85 it's going to take the same fuel regardless of whether you have a full or derated engine, since the derate selection doesn't change the aircraft drag polar or physical engine components at all.

You are right. I had to do some research because I realized that I remembered it wrong. Here is what I have:

http://www.smartcockpit.com/data/pdf...mics/Derated_Climb_Performance.pdf

"For a small increase in block fuel and flight time the use of derated climb will result
in a considerable saving on DMC costs and increase in time between overhauls.
By using a procedure that allows flexible use of climb derate based upon operational
constraints, the savings will be maximised. The actual DMC cost savings are specific
to an individual airline’s route structure, average ambient temperature and other
significant factors. Rolls-Royce willingly engages with individual airlines to discuss
specific details of their operation. Overall a major net saving will be seen.
Many 777 operators have taken the ‘Fast Taper’ option, however Rolls-Royce
recommends that the ‘Slow Tapers’ option should be incorporated to enable
enhanced benefits. To maximise benefits, CLB 2 should be used in preference to
CLB 1 whenever possible."



User currently offlinelightsaber From United States of America, joined Jan 2005, 12420 posts, RR: 100
Reply 12, posted (2 years 4 months 4 weeks 1 day 3 hours ago) and read 5417 times:
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Quoting embrider (Thread starter):
Why would an airline choose it over a "regular" engine?

There have already been enough posts explaining it. Basically:

Quoting BMI727 (Reply 6):
The benefit of derated engines is less wear and tear leading to lower maintenance costs and better on wing time.

   A derated engine has a longer cycle life. Usually matched to a reduced MTOW, as already noted, for regional flying where a widebody is being used for the volume of payload and not the maximum takeoff weight.

Quoting tdscanuck (Reply 9):
"permanent" derate of the engines changes out a physical programming plug on each engine computer. The plug tells the engine computer what thrust rating it should behave as.

  

Derating also helps with resale. The 'plug' will be replaced with a higher thrust plug upon resale. When CX and SQ sell their derated 777s, most likely the buyers will need more thrust for higher MTOW missions (longer range or one day there will be a freight 777).

The airframes will also undergo a 'paperwork' increase in MTOW. 772s (A-market) have a much lower resale value than 777-200ERs. The cost to change the plug and increase the MTOW is trivial. SQ bought their 777-200ERs in a very competitive market that allowed them to buy a much more capable jet than they needed for little (if any) increased cost. SQ will make their money back as they resell the airframes.

The same is true of CX's regional 773s. Albeit the 77W has put a crimp on the 773 resale market...

Lightsaber



I've posted how many times?!?
User currently onlineBMI727 From United States of America, joined Feb 2009, 15476 posts, RR: 26
Reply 13, posted (2 years 4 months 4 weeks 1 day 2 hours ago) and read 5363 times:

Quoting lightsaber (Reply 12):
A derated engine has a longer cycle life. Usually matched to a reduced MTOW, as already noted, for regional flying where a widebody is being used for the volume of payload and not the maximum takeoff weight.

To boil it down to a possibly even more basic level, when an aircraft is first designed, the thrust requirement is matched to MTOW. When an airline is effectively never going to use the full MTOW of a given plane, they don't need the full thrust either to meet various performance requirements, so they might as well derate the engine. And for that matter write down the MTOW as well.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineMarkC From United States of America, joined Apr 2006, 259 posts, RR: 0
Reply 14, posted (2 years 4 months 4 weeks 9 hours ago) and read 4710 times:

People confuse "derate" with pilot controlled "reduced thrust". As Lightsaber says, derate engines are fitted with a different plug, and can only get the power corresponding to the plug no matter what the pilots do. Reduced thrust is what the pilots control based on local conditions.

I'll give you another example. Say you were an airline based in SFO, and wanted to put a 4090 on a 777-200 non-er which came with 4077's. You would put a 77k plug in the 4090 to match the engine on the other side.


User currently offlinerjsampson From United States of America, joined Jul 2010, 35 posts, RR: 0
Reply 15, posted (2 years 4 months 4 weeks 8 hours ago) and read 4675 times:

While on this topic: Is the only difference between the GE90-115b and the GE90-110b simply a matter of software? If so, is selection for the -110b over the -115b for the same "paperwork" reasons?

User currently offlinejetlife2 From United States of America, joined Jul 2006, 220 posts, RR: 25
Reply 16, posted (2 years 4 months 4 weeks 8 hours ago) and read 4650 times:

Quoting rjsampson (Reply 15):
While on this topic: Is the only difference between the GE90-115b and the GE90-110b simply a matter of software? If so, is selection for the -110b over the -115b for the same "paperwork" reasons?

The engines are physically the same. The FADEC software contains all the tables for all ratings and bumps, so there is only one version of software. The rating plug (containing a permanently burned PROM chip) communicates to the FADEC which rating tables to enable.

The 777F and 200LR are smaller airplanes than the 300ER and are normally configured with 110's, but can be optionally configured with 115Bs. The customer chooses the model desired. The 300ER can only use the 115B. The extra capability of the 115B brings a price difference also. A 110B can be converted to a 115B and vice versa by changing the rating plug as well as record keeping via a SB.

All can be derated on a flight by flight basis, using either assumed temperature methods or fixed derate buttons (configurable to fixed levels of derate at customer option) or both at the same time. So very significant levels of derate can be used (much greater than 25% is possible, depending on mission).

In GE we usually try to use the word "derate" only to mean adjusting thrust flight by flight, and "rerate" when we are "permanently" changing the capability of the engine via the plug, but certainly that usage is different around the industry.

Hope that helps.

GHR


User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 17, posted (2 years 4 months 4 weeks ago) and read 4483 times:

Quoting jetlife2 (Reply 16):
The FADEC software contains all the tables for all ratings and bumps, so there is only one version of software. The rating plug (containing a permanently burned PROM chip) communicates to the FADEC which rating tables to enable.

For all intents and purposes then, the PROM is just a program the system runs. Two different software in "physical" form.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 18, posted (2 years 4 months 3 weeks 6 days 23 hours ago) and read 4479 times:

Quoting MarkC (Reply 14):
As Lightsaber says, derate engines are fitted with a different plug, and can only get the power corresponding to the plug no matter what the pilots do.

There are a few exceptions to this. The specific one I'm aware of is the CFM56-7 on the 737NG...if the throttles are advanced to the forward stop the engine will go to the maximum rated thrust for that model (-600, -700, etc.) regardless of what rating plug is in place.

Quoting rjsampson (Reply 15):
Is the only difference between the GE90-115b and the GE90-110b simply a matter of software?

Yes.

Quoting rjsampson (Reply 15):
If so, is selection for the -110b over the -115b for the same "paperwork" reasons?

In that particular case, yes.

In airliners with significant differences in length between the longest and shortest frame, but the same physical engine, the maximum thrust on the shorter versions may be capped to a lower value than the longer versions to avoid Vmca/Vmcg problems.

Tom.


User currently offlineaerotech777 From United States of America, joined Aug 2009, 67 posts, RR: 0
Reply 19, posted (2 years 4 months 3 weeks 6 days 11 hours ago) and read 4263 times:

According to this website: http://www.b737.org.uk/assumedtemp.htm, there are 2 types of derate: semi-parmanent derate and temporary derate known as "T/O De-rate.
The semi-parmanent derate would require changes to the EEC, HMU, fuel pump, engine ID plug and the loadable software.

Here the quote from this website:
A de-rate is a semi-permanent engine fix, used to reduce the maximum thrust available; for instance down to 20k from 22k on -3/700's. It is also used to equalise the thrust where B2 & C1 engines are mixed on the same airframe. When an engine is de-rated, the full (un-de-rated) thrust is no longer available because this would require changes to the EEC, HMU, fuel pump, engine ID plug and the loadable software; non of which can be done by the pilot in-flight.

A temporary form of de-rating known as a "T/O de-rate" is accessible through the FMC on TAKEOFF REF 2/2 or N1 LIMIT (NG's) but this is prohibited by some operators. The T/O de-rates (TO-1 & TO-2) can be 10 to 20%. It follows that an engine may be de-rated and also be using reduced thrust in which case you could be taking off at Full power -20% -25% = 60% of the full power of the engine - scary thought! Note that a T/O de-rate can overridden by firewalling the thrust levers.


User currently offlinehal9213 From Germany, joined May 2009, 302 posts, RR: 0
Reply 20, posted (2 years 4 months 3 weeks 5 days 20 hours ago) and read 4050 times:

Quoting embrider (Reply 3):
Thanks. It makes sense but wouldn't you have the same effect with "regular" engines, just applying less trust?

Although everybody already explained well, Ill give another practical example: Lets say, a critical part has to be examined and/or replaced after 1000 cycles, but on the rerated engine, would only need after 1500 cycles, because it experiences less stress. That saves maintenance cost.
If you "just apply less thrust", you cant track or make sure, how the engine was used, so you have to maintain the part after 1000 cycles in any case.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 21, posted (2 years 4 months 3 weeks 5 days 13 hours ago) and read 3934 times:

Quoting aerotech777 (Reply 19):
The semi-parmanent derate would require changes to the EEC, HMU, fuel pump, engine ID plug and the loadable software.

This is only true of older engines (usually the ones that don't have FADEC's). All new large engines I can think of just require changing the ID plug.

Quoting aerotech777 (Reply 19):
The T/O de-rates (TO-1 & TO-2) can be 10 to 20%.

They can be more than that...the amount of % derate that matches TO-1 and TO-2 is selectable by the airline.

Tom.


User currently offlineaerotech777 From United States of America, joined Aug 2009, 67 posts, RR: 0
Reply 22, posted (2 years 4 months 3 weeks 4 days 13 hours ago) and read 3779 times:

Quoting tdscanuck (Reply 21):
This is only true of older engines (usually the ones that don't have FADEC's). All new large engines I can think of just require changing the ID plug.

I think there are talking about engine fitted with FADEC because they mentioned EEC (Electronic Engine Control).


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 23, posted (2 years 4 months 3 weeks 4 days 12 hours ago) and read 3766 times:

Quoting aerotech777 (Reply 22):
Quoting tdscanuck (Reply 21):
This is only true of older engines (usually the ones that don't have FADEC's). All new large engines I can think of just require changing the ID plug.

I think there are talking about engine fitted with FADEC because they mentioned EEC (Electronic Engine Control).

There was some grey area in there for several years where engines had computers but they were only doing scheduling/monitoring and weren't full authority...not sure if those were properly called EEC's or not. I do know it's definitely true that, on the current generation engines, you don't need to change any hardware beyond the plug...the EEC, HMU, pump, and software are all the same.

Tom.


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