747-400 econ cruise speed?
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747-400 econ cruise speed?
Low cost index (25-30?), OPT ALT, no wind. Typical TOC weight. I'm guessing .84-.85.
767-200 was around .78, 767-300 was .79. Both advertised as .80 (marketing). 777-200 is high .82 (.826-.829). Routinely flown at .84. 787 is typically .843. Often flown at .85 and .84 when lighter. Some folks zip around at .86-87 in the 787. That burns approx 300/lbs per minute reduction in a 7-8 hour flight (.86) up to 1000 lbs +/- per minute saved at .87.
767-200 was around .78, 767-300 was .79. Both advertised as .80 (marketing). 777-200 is high .82 (.826-.829). Routinely flown at .84. 787 is typically .843. Often flown at .85 and .84 when lighter. Some folks zip around at .86-87 in the 787. That burns approx 300/lbs per minute reduction in a 7-8 hour flight (.86) up to 1000 lbs +/- per minute saved at .87.
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Depends on what that "typical TOC weight" is... Freighters routinely take off near Max T/O GW, where many pax routes do not require anything near Max. It may be .83-.84 at max weight, and down to .78 at light weights. Still, many pilots just fly a constant .84 cruise anyhow. Anything >.86 is just a waste of fuel.
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787 figures - I find it's really variable. I've had a light -8 in a jetstream cruise at .75 (CI 0) and a heavy -10 not budge from .85 (and a squidge) for an entire flight (CI again 0). Generally .84-.85 for normal ops. .843 a tad specific and probably flight specific...
Used to know a United Airlines pilot that flew 767s and 777s. He said that he routinely flew the 767 faster than the CI recommended (faster than 0.82) and still beat the fuel burn numbers - usually by a significant margin - and still arrived ahead of schedule.
I know that when we had EIS of the 747-8F, we discovered that the operators often flew it much slower and lower than we ever expected (29k, M 0.78 stick in my memory). We had to revise some of the FADEC s/w to better optimize fuel burn for those conditions.
I know that when we had EIS of the 747-8F, we discovered that the operators often flew it much slower and lower than we ever expected (29k, M 0.78 stick in my memory). We had to revise some of the FADEC s/w to better optimize fuel burn for those conditions.
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Used to know a United Airlines pilot that flew 767s and 777s. He said that he routinely flew the 767 faster than the CI recommended (faster than 0.82) and still beat the fuel burn numbers - usually by a significant margin - and still arrived ahead of schedule.
I know that when we had EIS of the 747-8F, we discovered that the operators often flew it much slower and lower than we ever expected (29k, M 0.78 stick in my memory). We had to revise some of the FADEC s/w to better optimize fuel burn for those conditions.
I know that when we had EIS of the 747-8F, we discovered that the operators often flew it much slower and lower than we ever expected (29k, M 0.78 stick in my memory). We had to revise some of the FADEC s/w to better optimize fuel burn for those conditions.
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On the 747-200, when heavy, we flew around M. 0.845, if memory serves right.
No flight computers, no digital nothing, but we had fast fingers with pocket calculators checking fuel remaining over every way point and
especially flying Westbound against the jet-streams in the winter from TLV to JFK.
Good old days and I have no idea what a -400 would do, just felt like chiming in from the Retired Gallery.
Carry on kids.
No flight computers, no digital nothing, but we had fast fingers with pocket calculators checking fuel remaining over every way point and
especially flying Westbound against the jet-streams in the winter from TLV to JFK.
Good old days and I have no idea what a -400 would do, just felt like chiming in from the Retired Gallery.
Carry on kids.
If I remember correctly, fuel burn is not the only consideration. Therefore, he could have been costing the company more money despite saving fuel
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With ECON and Cost index =0, the airplane is programmed to fly at the best speed considering winds. LRC takes the wind out of the picture and gives a slightly higher speed than no-wind ECON. CI is used to balance fuel burn with higher hourly costs such as crew salaries. Few (if any) airlines use it as originally intended.
We often beat the predicted fuel burn by flying a constant .82 instead of ECON.
We often beat the predicted fuel burn by flying a constant .82 instead of ECON.
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With ECON and Cost index =0, the airplane is programmed to fly at the best speed considering winds. LRC takes the wind out of the picture and gives a slightly higher speed than no-wind ECON. CI is used to balance fuel burn with higher hourly costs such as crew salaries. Few (if any) airlines use it as originally intended.
We often beat the predicted fuel burn by flying a constant .82 instead of ECON.
We often beat the predicted fuel burn by flying a constant .82 instead of ECON.
Every Airline (Boeing operator) I have worked for use CI as intended and often with variable CI for each sector unless a particular airspace requires fixed Mach number, eg Pacific/Atlantic etc.
Intruder: were your predicted fuel burns based on the planned ZFW or in fact recalculated for the actual ZFW bearing in mind the asumptions made about average weights? I did ULH flights for 20 years and the ZFW was the planned figure and there was only time to make a gross correction to the burn after flight closure so you often appeared to "beat the plan ".
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I am struggling to see where the .82 comes in. LRC is 99% of Max range. the 1% margin was put in historically to cater for inaccurate auto throttles that might drop you below the drag curve. As LRC has nothing to do with wind, the most efficient way to save fuel is stay in ECON but with a CI that approximates to LRC.
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Intruder: were your predicted fuel burns based on the planned ZFW or in fact recalculated for the actual ZFW bearing in mind the asumptions made about average weights? I did ULH flights for 20 years and the ZFW was the planned figure and there was only time to make a gross correction to the burn after flight closure so you often appeared to "beat the plan ".
The ECON speed will vary depending on weight, Flight Level , wind component & unit cost of the fuel balanced against the fixed operating cost per hour (which will vary depending on the operator)
There is no fixed answer, it's not just about minimum fuel burn, it's about minimum overall cost. If you want minimal fuel burn you go at CI zero which is Mmr (LRC is something different, a Boeing invention). but the overall cost of the flight may be higher when other factors are taken into account. If the fuel is free, go at 99 or 999 or whatever the maximum CI is in your airline.
Not sure what the OP's post is about; a question? a statement?
There is no fixed answer, it's not just about minimum fuel burn, it's about minimum overall cost. If you want minimal fuel burn you go at CI zero which is Mmr (LRC is something different, a Boeing invention). but the overall cost of the flight may be higher when other factors are taken into account. If the fuel is free, go at 99 or 999 or whatever the maximum CI is in your airline.
Not sure what the OP's post is about; a question? a statement?
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We had a cost index that was always less than 100. Sometimes as low as 40. The theory was that one should go to cost index zero if max range was desired. And that was certainly something to mention to the check airman when asked how one would maximize range.
Considering that the Cost Index range was 0-999, using a CI of 40 seemed like it was almost zero. So why not set 0 into the FMC when still 12 hours away from destination and see how much we would actually save based on the prediction from the FMC. Answer....about 100 kg or so. Great, we will land with 4.0 tons instead of 3.9 tons. Hardly worth the effort to reach over and select zero on a big jet.
Considering that the Cost Index range was 0-999, using a CI of 40 seemed like it was almost zero. So why not set 0 into the FMC when still 12 hours away from destination and see how much we would actually save based on the prediction from the FMC. Answer....about 100 kg or so. Great, we will land with 4.0 tons instead of 3.9 tons. Hardly worth the effort to reach over and select zero on a big jet.
Last edited by punkalouver; 12th Nov 2022 at 04:14.
We had a const index that was always less than 100. Sometimes as low as 40. The theory was that one should go to cost index zero if max range was desired. And that was certainly something to mention to the check airman when asked how one would maximize range.
Considering that the Cost Index range was 0-999, using a CI of 40 seemed like it was almost zero. So why not set 0 into the FMC when still 12 hours away from destination and see how much we would actually save based on the prediction from the FMC. Answer....about 100 kg or so. Great, we will land with 4.0 tons instead of 3.9 tons. Hardly worth the effort to reach over and select zero on a big jet.
Considering that the Cost Index range was 0-999, using a CI of 40 seemed like it was almost zero. So why not set 0 into the FMC when still 12 hours away from destination and see how much we would actually save based on the prediction from the FMC. Answer....about 100 kg or so. Great, we will land with 4.0 tons instead of 3.9 tons. Hardly worth the effort to reach over and select zero on a big jet.
This is also the reason that bizjets don't use CI, they only fly 400 hours a year on average and are individual aircraft or in a very small fleet compared to the airlines. The cost reduction for an individual jet would be relatively small. On the one I used to fly we had a cruise of 0.8 all the time, only using Mmr 0.74 on range critical flights because the fixed costs per hour were more than the cost of the fuel saved (aircraft only did about 250 hours a year)
It always amazes me how many pilots think that they are somehow smarter than the flight planning system. They are usually the ones that think they can "beat the odds in a casino" as well.....
Last edited by Private jet; 30th Oct 2022 at 09:56.
It always amazes me how many pilots think that they are somehow smarter than the flight planning system
The flight plan is only as good as the information fed into a computer. The pilot has at their disposal the actual conditions… the ‘big picture’ on the day.
Once you understand how and why the flight plan was generated, it’s not hard to beat it. It’s nice to win occasionally.
Maybe not smarter, however…..
The flight plan is only as good as the information fed into a computer. The pilot has at their disposal the actual conditions… the ‘big picture’ on the day.
Once you understand how and why the flight plan was generated, it’s not hard to beat it. It’s nice to win occasionally.
The flight plan is only as good as the information fed into a computer. The pilot has at their disposal the actual conditions… the ‘big picture’ on the day.
Once you understand how and why the flight plan was generated, it’s not hard to beat it. It’s nice to win occasionally.
How often is "occasionally"? and are you saying I don't understand "how and why" the plan was generated? If it's "not hard to beat" then please tell us why and how, and why airlines invest a lot of money & a lot of clever people work hard to generate these apparent works of fiction. YET AGAIN Cost Index is about minimum overall cost per hour, not just reducing fuel burn. I think 99% of professional pilots would agree the plans work very well on 99+ % of occasions. No deep thinking is needed flight planning wise from the pilot until something totally unexpected occurs which obviously cannot be planned for in routine ops. We used ARINC plans which worked out very well.
Last edited by Private jet; 30th Oct 2022 at 20:59.