Purpose of Semi-Fixed De-rates (TO1, To2)
Dutch CAA
I know that the IVW (Dutch CAA) does not allow fixed de-rates.
At my company we use fixed derates TO 1 & 2, and derate those using assumed temp method, if possible.
This gives a lot of flexibility on short or contaminated rwy's, and allows a lot of derate on long dry rwy's.
We also use 744's that don't have the fixed derates, and derate from the max power setting. This reduces the maximum deration considerably.
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Regarding the Dutchies: it was the RLD in those days, many moons ago. They didn't allow it on our B757/767's and I heard from HV guys that their B733's were all assumed temp of max thrust. I don't know for sure about their B738's, but I think they use assumed off 26K.
I'm not wanting to focus on that point; rather I'd like an answer as to why fixed-derates are a bonus. EU operators I've been associated with have 26K, 24K & 22K ratings. I hear some USA airlines have only 24K or 22K as max. They don't need 26K. If you need 26K on some occasions, fine, but why not just assume temp from 26K? Why have 3 sets of tables to achieve a thrust that matches the performance for the same weight. My performance dept claims to have it from Boeing as a good idea. No further explanation. I can see that lower thrust and lower VMCG might give a higher MTOW from contaminated rwys, but rarely unless very light weights. The reduced CLB could be calculated by the FMC as necessary from the amount of assumed temp. using fixed de-rates and then assumed temp just seems to complicate things and waste paper and printing ink. Save a tree.
I'm not wanting to focus on that point; rather I'd like an answer as to why fixed-derates are a bonus. EU operators I've been associated with have 26K, 24K & 22K ratings. I hear some USA airlines have only 24K or 22K as max. They don't need 26K. If you need 26K on some occasions, fine, but why not just assume temp from 26K? Why have 3 sets of tables to achieve a thrust that matches the performance for the same weight. My performance dept claims to have it from Boeing as a good idea. No further explanation. I can see that lower thrust and lower VMCG might give a higher MTOW from contaminated rwys, but rarely unless very light weights. The reduced CLB could be calculated by the FMC as necessary from the amount of assumed temp. using fixed de-rates and then assumed temp just seems to complicate things and waste paper and printing ink. Save a tree.
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Why even use printed stuff? Performance software does a very good job to test all possible combinations in a few seconds, and boeing gives it out on new planes anyway.
Besides, using a derate has its use during winter operation, and of course it allows less thrust used than using only ATM as ATM is restricted currently, whereas the combination of ATM and derate allows to work around that restriction without any special approval.
We used to have 27/24/22 on the 800s and nowadays use 26/24/22 or 22/20/18.5 on the -800 and -700 respectively. Full thrust is only needed for very few occasion, for example out of LPA with full passenger load, full baggage, a ton of cargo and 16 tons of fuel, which requires the SFP version additionally to full thrust sometimes. Most take offs are done using the lowest thrust setting available and depending on load with up to 60° ATM, usually flaps 1 as well.
Besides, using a derate has its use during winter operation, and of course it allows less thrust used than using only ATM as ATM is restricted currently, whereas the combination of ATM and derate allows to work around that restriction without any special approval.
We used to have 27/24/22 on the 800s and nowadays use 26/24/22 or 22/20/18.5 on the -800 and -700 respectively. Full thrust is only needed for very few occasion, for example out of LPA with full passenger load, full baggage, a ton of cargo and 16 tons of fuel, which requires the SFP version additionally to full thrust sometimes. Most take offs are done using the lowest thrust setting available and depending on load with up to 60° ATM, usually flaps 1 as well.
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Bushman
Some airlines had manufacturer's warranties that rewarded the customer for using a "smaller" engine for takeoff for a certain number of years. The more you could safely use TO1 or TO2, the happier the manufacturer was, and the better "deal" on coverage. The TO, TO1 and TO2 settings essentially provided 3 different certificated engines: big, medium and small.....as they were "fixed" derates. Each one was considered "max" for that "size" of engine. The AT derates provided even further cuts....up to 40% total from TO. On a fully AT-derated TO2 takeoff (obviously light weight with friendly runway/obstacles), we called them "Idle Power Takeoffs."
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Originally Posted by mutt
I wonder if the airlines can statistically show that their engine maintenance costs are higher in the winter season
EDIT:: Derating beyond 25% has no benefit and is just silly, IMO.
Last edited by HazelNuts39; 21st Jan 2011 at 10:07.
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IAD Flyer,
I'm not going to cut and paste, however, if you refer to Boeing Systems Manual, FMC, " Thrust Management", the whole subject is covered and the question you originally asked is answered.
The subject of Fixed Derate, Assumed and a combination of both is clearly explained.
I'm not going to cut and paste, however, if you refer to Boeing Systems Manual, FMC, " Thrust Management", the whole subject is covered and the question you originally asked is answered.
The subject of Fixed Derate, Assumed and a combination of both is clearly explained.
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Bealzebub;
There seems to be discrepancy in our manuals. This is from my systems description manual B757-200.
Displayed (green) selected FMS thrust reference mode:
Takeoff:
TO maximum rated takeoff thrust
TO 1 takeoff thrust one, climb one preselected
TO 2 takeoff thrust two, climb two preselected
Assumed Temperature Takeoff:
DTO assumed temperature derated takeoff thrust
DTO 1 assumed temperature derated takeoff thrust one, climb one
preselected
DTO 2 assumed temperature derated takeoff thrust two, climb two
preselected
(Edited to say sorry for drifting)
There seems to be discrepancy in our manuals. This is from my systems description manual B757-200.
Displayed (green) selected FMS thrust reference mode:
Takeoff:
TO maximum rated takeoff thrust
TO 1 takeoff thrust one, climb one preselected
TO 2 takeoff thrust two, climb two preselected
Assumed Temperature Takeoff:
DTO assumed temperature derated takeoff thrust
DTO 1 assumed temperature derated takeoff thrust one, climb one
preselected
DTO 2 assumed temperature derated takeoff thrust two, climb two
preselected
(Edited to say sorry for drifting)
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And further, the Thrust Mode Select Panel;
Thrust Reference Mode Select Switches
PUSH
manually selects desired thrust reference mode
selected thrust reference mode and reference EPR are displayed
TO/GA
selects TO mode on the ground or GA mode inflight
cancels preselected climb one or two
cancels selected assumed temperature
selecting 1 or 2 with TO or D-TO reference mode displayed:
preselects CLB 1 or CLB 2 on the ground if autothrottles not engaged
subsequent push cancels any preselected 1 or 2
cancels selected assumed temperature
selects TO 1 or TO 2
Thrust Reference Mode Select Switches
PUSH
manually selects desired thrust reference mode
selected thrust reference mode and reference EPR are displayed
TO/GA
selects TO mode on the ground or GA mode inflight
cancels preselected climb one or two
cancels selected assumed temperature
selecting 1 or 2 with TO or D-TO reference mode displayed:
preselects CLB 1 or CLB 2 on the ground if autothrottles not engaged
subsequent push cancels any preselected 1 or 2
cancels selected assumed temperature
selects TO 1 or TO 2
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Sorry Beazlebub its not that simple,
You clearly have not flown a 757 or 767 with boeing optional company fixed derates installed. Thomson guys among others know all about it. If you try and preselect climb 1 on the ground you actually select the fixed derate and then subsequent assumed temp reduction gives you what we call a double de-rate. (ie you derate the fixed derate) The trick is in the eicas. Selecting 1 or 2 on your machine gives a WHITE 1 or 2. On fixed rate machines the fixed rate shows as an all green TO-1/2 etc when 1 or 2 are pressed. Boeing have a huge number of optional extra's available. Your aircraft are just one of several different fits
The 777 EICAS thrust headings are exactly the same using fixed derates then assumed temp. (climb thrust selection is much cleverer though). All selections through the FMS of course.
Why wouldnt you want to use as little thrust as possible and still meet all the performance criteria both from a commercial and risk reduction point of view
You clearly have not flown a 757 or 767 with boeing optional company fixed derates installed. Thomson guys among others know all about it. If you try and preselect climb 1 on the ground you actually select the fixed derate and then subsequent assumed temp reduction gives you what we call a double de-rate. (ie you derate the fixed derate) The trick is in the eicas. Selecting 1 or 2 on your machine gives a WHITE 1 or 2. On fixed rate machines the fixed rate shows as an all green TO-1/2 etc when 1 or 2 are pressed. Boeing have a huge number of optional extra's available. Your aircraft are just one of several different fits
The 777 EICAS thrust headings are exactly the same using fixed derates then assumed temp. (climb thrust selection is much cleverer though). All selections through the FMS of course.
Why wouldnt you want to use as little thrust as possible and still meet all the performance criteria both from a commercial and risk reduction point of view
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I would be curious to know the real overhaul times......certainly more then a few pilots are pushing balanced field into the weeds to get points, when maybe pushing it 'that far' is not necessary to get the extended overhaul advantage.
