747-400 econ cruise speed?

[misd-agin]

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.

[zambonidriver]

Anyone with similar figures for Airbus?

[Intruder]

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.

[Cough]

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...

[eckhard]

Low cost index (25-30?), OPT ALT, no wind. Typical TOC weight. I'm guessing .84-.85.

CI 90 usually gave M0.85 on the 747-400

[tdracer]

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.

[punkalouver]

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.
If I remember correctly, fuel burn is not the only consideration. Therefore, he could have been costing the company more money despite saving fuel

[TowerDog]

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.:cool:

[wiggy]

If I remember correctly, fuel burn is not the only consideration. Therefore, he could have been costing the company more money despite saving fuel

That's also my recollection of how we were told it operated (certainly where I worked).

[Intruder]

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.

[8che]

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.

Not sure I understand any of the above statement. Cost index 0 or 999 will give you the "best speed" for your airline. How does flying .82 beat the predicted fuel burn, unless you're talking no wind ?
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.

[Broomstick Flier]

8che,

It is my understanding that CI 0 is maximum range and 999, maximum speed. Not?

[Meikleour]

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 ".

[8che]

8che,

It is my understanding that CI 0 is maximum range and 999, maximum speed. Not?

Yep, CI = Time Related Cost ($/hour) / Fuel Cost (cents/pound). So yes 0 is approximately equal to MRC (maximum range cruise). But it's not the "best speed", as that depends on the company's time related costs which most pilots won't have much of a clue about. So, if the company has put a fair amount of effort into CI's we should at least fly ECON whenever possible or CI 0 if fuel is critical and/or your seriously early with a tail wind.

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.

[Intruder]

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 ".
I don't know the technicalities of how the computer flight plans did fuel predictions. We had to ask for a recalculation if the ZFW was more than 5 tonnes greater than plan. I do know that except in cases of strong headwinds, it was common for us to "beat the plan".

[Private jet]

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?

[punkalouver]

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.

[Private jet]

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.

Even a change of 40 makes a huge difference with a fleet of aircraft, all flying 4000 hours a year. Using your numbers each aircraft would use 33.3 tonnes more, or less, per year. Multiply that by the number of aircraft in the fleet.... see the point? BUT once again it's about total operating cost not just fuel burn & CI is set to minimise the total cost of that particular flight, taking all the circumstances into account.
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.....

[Capt Fathom]

It always amazes me how many pilots think that they are somehow smarter than the flight planning system

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.

[Private jet]

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.

That's true enough, to a point....
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.

[hans brinker]

That's true enough, to a point....
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.

Most of the times when we are filed at a high cost index it's because flight time is close to block time, and the company wants to show good on time arrival. At least half the time we are able to push a few minutes early, have a short taxi, get airborne, and I can reduce to CI15 and still be early. Reverse is true too. CI is a great tool, but if it not updated dynamically the pilot will definitely ba able to beat it often.

[Private jet]

Most of the times when we are filed at a high cost index it's because flight time is close to block time, and the company wants to show good on time arrival. At least half the time we are able to push a few minutes early, have a short taxi, get airborne, and I can reduce to CI15 and still be early. Reverse is true too. CI is a great tool, but if it not updated dynamically the pilot will definitely ba able to beat it often.
I don't understand the logic or benefit of arriving early, as you say. I have to conclude that in order to arrive on time you were receiving updated CI's from the airline via ACAR's? and hence just entered the updated number into the FMS. If not you were just guessing. If you want to arrive early, (for no good reason) why didn't you just push up the fixed cruise speed in the FMS? (which makes very little difference unless its a very long sector) Once again how is any of that "beating the system" ? unless of course it gives an airline Captain a bit of an erection or wetness.....

[punkalouver]

Even a change of 40 makes a huge difference with a fleet of aircraft, all flying 4000 hours a year. Using your numbers each aircraft would use 33.3 tonnes more, or less, per year. Multiply that by the number of aircraft in the fleet.... see the point? BUT once again it's about total operating cost not just fuel burn & CI is set to minimise the total cost of that particular flight, taking all the circumstances into account.
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.....

My point wasn't to focus on the accumulation of fuel savings on a fleet of aircraft over the year. It was to emphasize that on any particular flight, the procedure of going to CI zero when there was a low fuel issue really made no appreciable difference.

[hans brinker]

I don't understand the logic or benefit of arriving early, as you say. I have to conclude that in order to arrive on time you were receiving updated CI's from the airline via ACAR's? and hence just entered the updated number into the FMS. If not you were just guessing. If you want to arrive early, (for no good reason) why didn't you just push up the fixed cruise speed in the FMS? (which makes very little difference unless its a very long sector) Once again how is any of that "beating the system" ? unless of course it gives an airline Captain a bit of an erection or wetness.....

I will try to look past your past sentence, and answer again, but now in a way you might understand.
My company wants us to depart and arrive on time, not early, not late. Due to the schedule being built months ahead of time, the winds and average delays used to calculate block times are just that, average. On the actual day of departure, when the dispatcher prepares for our specific flight, about 2 hours before departure, he has much better info on the delays expected and the actual winds, and route changes due to weather. He will plan accordingly, and come up with a CI that in combination with the expected taxi times will give us an on time arrival. Not early, because the gate will be occupied, not late because of "on time performance numbers". Plenty of times, after getting an early off block, and shorter than expected taxi, it turns out we would get in very early if we fly at that planned high CI, so I get in touch with dispatch, and we adjust it. The reverse is also true. That is why I said it would be nice if the CI would be automatically updated after getting airborne, and that is why we can "beat the system", meaning, we can get better on time performance than the outdated data would give., because the system isn't updated with the actual info. I would not get any updated CI if I didn't request them. And it isn't exactly guessing to bring down/up the CI till you see a landing time that when you add the scheduled taxi time gives you the on time arrival time. Not rocket science. And definitely not something that would get me exited...

[8che]

I will try to look past your past sentence, and answer again, but now in a way you might understand.
My company wants us to depart and arrive on time, not early, not late. Due to the schedule being built months ahead of time, the winds and average delays used to calculate block times are just that, average. On the actual day of departure, when the dispatcher prepares for our specific flight, about 2 hours before departure, he has much better info on the delays expected and the actual winds, and route changes due to weather. He will plan accordingly, and come up with a CI that in combination with the expected taxi times will give us an on time arrival. Not early, because the gate will be occupied, not late because of "on time performance numbers". Plenty of times, after getting an early off block, and shorter than expected taxi, it turns out we would get in very early if we fly at that planned high CI, so I get in touch with dispatch, and we adjust it. The reverse is also true. That is why I said it would be nice if the CI would be automatically updated after getting airborne, and that is why we can "beat the system", meaning, we can get better on time performance than the outdated data would give., because the system isn't updated with the actual info. I would not get any updated CI if I didn't request them. And it isn't exactly guessing to bring down/up the CI till you see a landing time that when you add the scheduled taxi time gives you the on time arrival time. Not rocket science. And definitely not something that would get me exited...


Hans, I think you're missing the point. CI was never intended to be used as an on-time departure/arrival tool. It's a designed tool to enable the cheapest way to operate the aircraft per flight hour when comparing a company's direct operating costs to fuel related cost. Adjusting the CI to enable better on time performance is like using chopsticks to eat soup, it might look like its working occasionally but you aint getting much soup.

Try the RTA function on the progress page if you want the best on time.