easyJet Cost Index & Econ Descent
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We had to hold because we were behind two EZY's: the first one doing 265kts in descent, ATC asked the second one if he could fly 320 in order to be number one. He said NO and as a consequence he was slowed down to 220 and we were send in the hold...
If that's so,those pilots are very selfish indeed. He must be telling himself "Let me save 50kg of fuel even if it means each person behind me burns an extra 500kg. I'll be able to sleep at night because my boss, who sits behind a desk all day thinks that's how it should be done."
People, there's a reason WE are in command. I for one wouldn't hesitate to ignore the CI speeds if it means a more expeditious flow of traffic. I don't know about these guys, but I'd feel pretty bad if I caused somebody else a major inconvenience (hold or missed approach), especially for something as trite as that. Come on guys, please display professional courtesy and good airmanship.
If that's so,those pilots are very selfish indeed. He must be telling himself "Let me save 50kg of fuel even if it means each person behind me burns an extra 500kg. I'll be able to sleep at night because my boss, who sits behind a desk all day thinks that's how it should be done."
People, there's a reason WE are in command. I for one wouldn't hesitate to ignore the CI speeds if it means a more expeditious flow of traffic. I don't know about these guys, but I'd feel pretty bad if I caused somebody else a major inconvenience (hold or missed approach), especially for something as trite as that. Come on guys, please display professional courtesy and good airmanship.
Rather than speculate about the fuel savings available why not try a scientific test.
Takes a few flights to complete, but gives interesting results.
I have found that the difference between a 40CI descent (often around 260 kts) and a 300 kt descent is around 100 kg.
This has been calculated by noting the cruise fuel burn (must be stable), the descent fuel burn and the extra time spent in the cruise for a 300 kt descent as opposed to a 260kt descent. The time saving of the higher speed is less than a minute (and is at idle).
40 sectors a month gives a saving of 4 tons, which I may be wrong but thinkm equates to $3200.
Similar savings are achieved by cruising economically.
Green issues have been afforded much greater importance in recent times, so policies such as that at EZY will become the norm soon, it wil be the 340kt merchants who find themselves being vectored.
Do the controllers vectoring us towards the hold at high speed realise the size of their carbon footprint?
(By the way, I think it's down to form drag increase)
Takes a few flights to complete, but gives interesting results.
I have found that the difference between a 40CI descent (often around 260 kts) and a 300 kt descent is around 100 kg.
This has been calculated by noting the cruise fuel burn (must be stable), the descent fuel burn and the extra time spent in the cruise for a 300 kt descent as opposed to a 260kt descent. The time saving of the higher speed is less than a minute (and is at idle).
40 sectors a month gives a saving of 4 tons, which I may be wrong but thinkm equates to $3200.
Similar savings are achieved by cruising economically.
Green issues have been afforded much greater importance in recent times, so policies such as that at EZY will become the norm soon, it wil be the 340kt merchants who find themselves being vectored.
Do the controllers vectoring us towards the hold at high speed realise the size of their carbon footprint?
(By the way, I think it's down to form drag increase)
Join Date: Apr 2005
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Oh and let's also look on the bright side of the latest wet dreams of this fumes, errrr fuel/carbon footprint madness: imagine all those extra block hours and how quickly you will reach those 900 hours! On top of that, imagine the effect it will have on OTP and therefore (the already closely planned) the max daily duty limit. Lemme guess: going into discretion seems will be the only 'authority' that will stay in place for a while...
I guess then next move will be to increase our annual maximum to 1000 hours and perhaps do away with alternate fuel or a further reduction of contingency fuel. Big Brother, in his cozy office, is already checking the weather and NOTAMS in those trip envelops to see whether those 500kg extra for TS's were really justified or not. All in the name of "safety?" Who needs fuel anyways?
How low can you go?
I guess then next move will be to increase our annual maximum to 1000 hours and perhaps do away with alternate fuel or a further reduction of contingency fuel. Big Brother, in his cozy office, is already checking the weather and NOTAMS in those trip envelops to see whether those 500kg extra for TS's were really justified or not. All in the name of "safety?" Who needs fuel anyways?
How low can you go?
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We tried the same thing in the last few years. Although we used repetitive flightplans that are only filed twice a year (one for winter and one for summer) we changed our cost index quite a bit from around 35 down to between 12 and 16 and were reminded to allways fly CI, which turned out to be around 250kias during descent (737 classics).
One thing we noticed right away was that the working environment became much more quiet and bearable reducing our stress level quite a bit, another thing was we got payed more since we our pay was based on actual block time.
Very soon our operation team had to change the policy a bit allowing us to use our own judgement for descent since ATC just couldn't really work with that, every descent out of cruising altitude actually reduced our speed immediately quite a lot (usually around 30 to 40 kias or .20).
Now we get payed a fixed amount for each sector regardless of how long it takes to get there and many of us just fly close to red line, who cares about fuel since we're purely operating as ACMI anyway.
One thing we noticed right away was that the working environment became much more quiet and bearable reducing our stress level quite a bit, another thing was we got payed more since we our pay was based on actual block time.
Very soon our operation team had to change the policy a bit allowing us to use our own judgement for descent since ATC just couldn't really work with that, every descent out of cruising altitude actually reduced our speed immediately quite a lot (usually around 30 to 40 kias or .20).
Now we get payed a fixed amount for each sector regardless of how long it takes to get there and many of us just fly close to red line, who cares about fuel since we're purely operating as ACMI anyway.
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I would question the comment that SOP's are rigid and gospel. I've flown for too many operators whose SOP's changed with every change of Chief Pilot. They each had their own favourite way of doing things. Some were good ideas, some were crass. Common sense/airmanship should always prevail. That's what we are paid for.
There was one C.P of a London based Loco, who demanded Gear down at G/S alive. What a classic way to waste fuel. Had he never heard of Low Drag. low noise, low fuel approaches? Then the London Airports demanded these type of approaches, which most of us had been flying anyway at every airport for decades. Guess what, the SOP's changed to suit ATC.
As for C.I's. I thought that zero was min fuel. Also, I did fly for 1 operator who tried the Boeing ideal that C.I. should be selected for each sector dependant on fuel % price; i.e. a variable. What a fisco that was. LRC seemed to work fine for most trips.
I heard it said that ej's first B737 C.I was chosen to match Stelio's age. If correct, how scientific was that.
There was one C.P of a London based Loco, who demanded Gear down at G/S alive. What a classic way to waste fuel. Had he never heard of Low Drag. low noise, low fuel approaches? Then the London Airports demanded these type of approaches, which most of us had been flying anyway at every airport for decades. Guess what, the SOP's changed to suit ATC.
As for C.I's. I thought that zero was min fuel. Also, I did fly for 1 operator who tried the Boeing ideal that C.I. should be selected for each sector dependant on fuel % price; i.e. a variable. What a fisco that was. LRC seemed to work fine for most trips.
I heard it said that ej's first B737 C.I was chosen to match Stelio's age. If correct, how scientific was that.
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i-ford
no matter what speed you fly in the descent, econ speed given by a cost index worked out by the company is the most economical...that's what cost index is all about, trading cost of time between cost of fuel. i'm not one for slow descents but if it keeps me in a job then i'll do it where possible.
no matter what speed you fly in the descent, econ speed given by a cost index worked out by the company is the most economical...that's what cost index is all about, trading cost of time between cost of fuel. i'm not one for slow descents but if it keeps me in a job then i'll do it where possible.
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As a non CP I am intrigued by these various descent SOPs. I was in a 737NG yesterday which went for fast descent overall (about 25 mins from start of descent from FL380 I guess to touchdown - 8000/25 = 320 I note), it had been assigned a very long more or less straight in approach, with speedbrakes deployed for at least the last five minutes right up to the point of first stage of flaps and slats.
I have over the last year or two also noticed a number of complaints by afflicted aircrew in the medical forum here on PPRuNe asking about repressurisation problems with their ears.
Now are descent profiles like that usual or unusual thesedays? And are you saying that such descents are believed or found to be less economical than at first thought?
I have over the last year or two also noticed a number of complaints by afflicted aircrew in the medical forum here on PPRuNe asking about repressurisation problems with their ears.
Now are descent profiles like that usual or unusual thesedays? And are you saying that such descents are believed or found to be less economical than at first thought?
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and if everyone else flew CI 19 on the bus or 26 on the 737 then we'd all save a shed load of fuel and not get our knickers in a twist about someone flying 12 kts slower than us!
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Hank Birofski
Yeah well, it doesn't really work this way, does it?
1) u sure wanna stay at those cruise level as long as possible, as these are the ones where u burn little fuel
2) if u fly the bus, u will have observed that following a profile descent, despite the IDLE FMA indication, still gives you some thrust (look at the N1 or EPR depending on engines) during the descent, thereby burning thrust to keep those misery 251kts (its what we had last nite...).
Conclusion: to save fuel climb as quickly as u can to the cruise level and stay there as long as u can. And if permitted, descend as steeply as u can, ideally switch the engines off
Remember, jet engines are optimized for hi level cruise, not lo level loitering
live 2 fly 2 live
You will use more fuel as the engines stayed at a crz pwr setting for longer
1) u sure wanna stay at those cruise level as long as possible, as these are the ones where u burn little fuel
2) if u fly the bus, u will have observed that following a profile descent, despite the IDLE FMA indication, still gives you some thrust (look at the N1 or EPR depending on engines) during the descent, thereby burning thrust to keep those misery 251kts (its what we had last nite...).
Conclusion: to save fuel climb as quickly as u can to the cruise level and stay there as long as u can. And if permitted, descend as steeply as u can, ideally switch the engines off
Remember, jet engines are optimized for hi level cruise, not lo level loitering
live 2 fly 2 live
As usual, a lot of rubbish spoken here.
According to Airbus (if anyone could be bothered to read the document), the 319 saves 1 Kg of fuel per knot reduced in the descent (260kt to 300kt range).
If you perform an intermediate level off, the descent speed may well drop from 275 ish to 255 ish.
The SOP allows speed to be specified by ATC, or indeed the commander may choose a suitable speed for the ATC environment. Sounds like some Captains are not doing either!
According to Airbus (if anyone could be bothered to read the document), the 319 saves 1 Kg of fuel per knot reduced in the descent (260kt to 300kt range).
If you perform an intermediate level off, the descent speed may well drop from 275 ish to 255 ish.
The SOP allows speed to be specified by ATC, or indeed the commander may choose a suitable speed for the ATC environment. Sounds like some Captains are not doing either!
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Denti,
Quote:
Now we get payed a fixed amount for each sector regardless of how long it takes to get there and many of us just fly close to red line, who cares about fuel since we're purely operating as ACMI anyway.
Nice to see your company value a bit of commercial awareness amongst their pilots. Guess it shows not everyone shows the same level of professionalism.
Quote:
Now we get payed a fixed amount for each sector regardless of how long it takes to get there and many of us just fly close to red line, who cares about fuel since we're purely operating as ACMI anyway.
Nice to see your company value a bit of commercial awareness amongst their pilots. Guess it shows not everyone shows the same level of professionalism.
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Cindex = Ctime/Cfuel
To get a better picture of the whole thing read:
http://www.iata.org/NR/ContentConnec...x_Material.pdf
SOP = Standard Operating Procedures (I think). So whilst most phases of flight(s) are standard, some might not be and thus a modified descent speed might have to be used (i.e. selected).
Or, looking at it from a different angle, going to certain airports, it is SOP to fly such and such a speed in the descent to comply with ATC requirements. I'm sure that complying with (good) ATC is part of most of our SOP's.
Obviously if your descent profile (descent arrow) is based on CI 0 (low) i.e. early descent and you initiate your descent based on that and fly the managed speeds associated with that CI and are then asked to fly high speed, you will burn more fuel than originally computed by the FMGC.
The way I understand it, for a given CI, there will always be one (1) optimum point of descent (for a given profile on a perfect day). For that specific CI, descending before OR after that point you'll burn more fuel.
BUT, we don't live in a perfect world and thus I think we should try and be as close to SOP's as possible, but have enough flexibility (in our minds) to accept deviations from these same SOP's, knowing that we will return to SOP when appropriate. Part of SA is not only knowing where we were 1 minute ago, where we are now and where we will be in 1 minute, but also knowing who is around us and how we can contribute to a most efficient way of operating to assist all parties involved (aircraft & ATC). (SA involves much more obviously...)
To get a better picture of the whole thing read:
http://www.iata.org/NR/ContentConnec...x_Material.pdf
SOP = Standard Operating Procedures (I think). So whilst most phases of flight(s) are standard, some might not be and thus a modified descent speed might have to be used (i.e. selected).
Or, looking at it from a different angle, going to certain airports, it is SOP to fly such and such a speed in the descent to comply with ATC requirements. I'm sure that complying with (good) ATC is part of most of our SOP's.
Obviously if your descent profile (descent arrow) is based on CI 0 (low) i.e. early descent and you initiate your descent based on that and fly the managed speeds associated with that CI and are then asked to fly high speed, you will burn more fuel than originally computed by the FMGC.
The way I understand it, for a given CI, there will always be one (1) optimum point of descent (for a given profile on a perfect day). For that specific CI, descending before OR after that point you'll burn more fuel.
BUT, we don't live in a perfect world and thus I think we should try and be as close to SOP's as possible, but have enough flexibility (in our minds) to accept deviations from these same SOP's, knowing that we will return to SOP when appropriate. Part of SA is not only knowing where we were 1 minute ago, where we are now and where we will be in 1 minute, but also knowing who is around us and how we can contribute to a most efficient way of operating to assist all parties involved (aircraft & ATC). (SA involves much more obviously...)
ex-Tanker
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The Bottom Line
If your cruise and descent management saves fuel vis a vis the flight plan - and mine usually did, then I can't see how the slow descent scenario can ever be better.
It is a very short sighted policy to save theoretically peanuts in descent and end up in a long approach at low level anyway.
The true saving occurs with the latest possible idle descent - even though the speed comes up over your "optimum" FMC or book speed - and into an expeditious approach.
Coming up from the south to LTN you can often get a left hand descent straight into RW 26 and if you do it right, hardly touch Stanstead airspace - gaining anything up to 450kgs and many minutes a shot. Follow your FMC routing and descent on this one and you lose - every time.
The fact that flying slow cocks up your colleagues - possibly from your own airline, makes this individually calculated policy even more daft.
Bottom line, pilots have more flight experience than FMC computer designers - use it!
FC.
It is a very short sighted policy to save theoretically peanuts in descent and end up in a long approach at low level anyway.
The true saving occurs with the latest possible idle descent - even though the speed comes up over your "optimum" FMC or book speed - and into an expeditious approach.
Coming up from the south to LTN you can often get a left hand descent straight into RW 26 and if you do it right, hardly touch Stanstead airspace - gaining anything up to 450kgs and many minutes a shot. Follow your FMC routing and descent on this one and you lose - every time.
The fact that flying slow cocks up your colleagues - possibly from your own airline, makes this individually calculated policy even more daft.
Bottom line, pilots have more flight experience than FMC computer designers - use it!
FC.
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Speed, speed
It's a lot more civilized when everyone does 290Kt in the descent. I bumbled into PFO the other week behind an Airbus that I'm sure was taking part in a slow flying competition - I think it won too! I'm not slagging off the Airbus (I fly one too) but some of the descent speeds it generates are rediculous. Selected speed - way to go, unless ATC tell otherwise of course.
We use CI 15 in our 320/319s and descent speed is often 250 knots which is far too slow to fit in to the general ATC environment (mind you it would work if everybody used it) so most people tend to use 280 which apparently makes no difference at all to the overall CI cost/time/fuel calculation. To make that work though you need to re-program the descent before you start down to show 280 knots. Going down at the 250kt top of descent and then selecting 280 and getting low or using v/s to stay on the profile is very inefficient.
As topslide says the whole slow descent thing is based on the fact that you spend less time in the cruise using fuel because the descent starts a few miles earlier but the number of times you are asked to speed up or get a few extra miles added to your track because you are put behind other traffic means that overall I am quite sure that entering a slightly higher speed makes good sense. There is no doubt that we have saved fuel by using a lower index but mainly due to slower cruise and taxing in on one engine, slow descent is not saving much at all.
As topslide says the whole slow descent thing is based on the fact that you spend less time in the cruise using fuel because the descent starts a few miles earlier but the number of times you are asked to speed up or get a few extra miles added to your track because you are put behind other traffic means that overall I am quite sure that entering a slightly higher speed makes good sense. There is no doubt that we have saved fuel by using a lower index but mainly due to slower cruise and taxing in on one engine, slow descent is not saving much at all.
