What Cost index are you using B737NG?
 

Just as a matter of interest, what cost index are you all using?

Our airline states 4 for all routes.

For many airlines depends on the flight.... My company this changes from flight plan to flight plan.....

Will be changed for every flight, but usually somewhere between 10 and 13, highspeed OFPs at 200 (usually used to arrive before night curfew), we're supposed to change it to 8 if we're early.

The airline im working for has a fixed Ci which is close to LRC...guess fuel still very cheap for them.:cool:

We're using 8-9.

Just wonder, do you use the CI (ECON) descent speeds? Which would be below 250 for CI below 10.

8/9, ECON DES unless otherwise requested by ATC or flight delayed...

A Boeing survey showed that for the B737NG values of CI in the range of 10-30 are often used. Note that a CI=0 equals MRC. LRC is roughly around a CI of 35 on the B737NG. The actual, optimum CI can differ between airlines and routes. If you have a lot of connecting passengers, you might be better of flying at a higher CI than when you don’t have any connecting passengers on board for the same route/aircraft.

I noticed that you (Jinkster) are using a low CI at your airline. Flying at low cost indices can result in speed instabilities. Perhaps you have experienced a lot of movement of the AT when flying at this low CI? Note that not every airline reports these problems when flying at low CIs however. Flying fixed cost indices on all routes is not always the best thing to do either.

Boeing has written a number of interesting articles on this topic. See for instance:

http://boeing.com/commercial/aeromag...7_article5.pdf

We use 30 for every flight giving us a record breaking speed of 273 KTS in the descent. However most of us ignore it and fly 320/.80.

In this time of economic problems, it seems even more important to fly at the correct cost index. The use of constant cost indices throughout the fleet or ignoring indices given in the flight plan doesn’t help getting the costs down. Note that a given cost index (assumed that it has been calculated correctly) ensures that the total cost (sum of fuel cost + cost of time) are minimum.

As I get paid by the minute... I wish we used a CI of 1.

However our range is between 11 to 15 depending on sector length.

Average ECON speed for the NG varies from .77 to .78 at the higher altitudes, or about 5 knots... At the end of the day, not very significant for a 4 hour flight.

There are times during ETOPs operations, we are requested to fly a given and RTA request which throws the CI out the window all together... even though not resulting in much a total fuel burn deviation from the plan.

Bigger aircraft... larger difference however.

Cost index surely should change dependent on network, fuel price fluctuations, operational costings and hedging agreements. Personally I believe that our standard cost index is due to our operational department being so understaffed and it's planning equipment being so inept. Besides, ECON speeds are rarely adhered to anyway, so fuel burn figures based on a perceived standard cost index will be largely inaccurate anyway. Maybe I'll punch in CI 500 next time I fly :p

Not if you're not paid by the minute:=:E

Depends how you are payed by the minute. We are payed by the minute, however we are payed by the minute of standard block times which are a bit longer than flown ones. Usually i get payed 20 to 30% more time than i fly. However if i decide to hold for 2 hours and then land at the destination i certainly not going to make a profit, if i divert i get payed actual block time, sooo, hold for 1 hours and then divert :ok:

For us it is 11 - been steady for a few years now....

That's only half the truth. MRC is a fixed speed for a given weight, ECON speed is not.

With a strong headwind ECON (with cost index 0) will fly faster than actual MRC and LRC for that matter. Since we have no representation of actual MRC, the practical application would be LRC.

The reason being, that ECON will take actual wind into consideration whereas LRC doesn't. From practical experience even a Cost Index of more than 10 sometimes give a lower speed than LRC if you have a strong tailwind (FMC deems it more economical to hang around in the tailwind for a little longer and giving us a free ride).

If fuel is critical, I would suggest to compare and consider the options of LRC and ECON CI=0, if headwinds conditions, before deciding on the better option. Being stuck in a strong headwind at LRC may give you less fuel at destination than letting the FMC do it's magic.

Strangely you wont find that information in the FCOM, but in the FCTM under "Cruise Speed Determination":
In the same section you also find the that for NG, wind correction is not applied for LRC:
(Strangely it does apply wind corrections to LRC in the classic, thereby not being a "true" LRC according to the definitions).

Jhonny tightlips,
And why would you fly at 320/.80?please explain:suspect glad i aint your fo:rolleyes:

Indeed ci 0 is the way to save the most fuel (MRC) and best L/D for descent however the optimum(maintenance cost/fuel cost) is ci12.

We use a fixed CI of 20 for our -300/500/700 aircraft. That gives you a descent speed on 266 in the 300/500 and 261 in the -700. We modify the descent speed to meet published arrival or ATC requested descent speeds. Some folks (certainly not I) flt 280/300 knot descents routinely.
We are supposed to be looking at getting leg specific CIs from a computer program based on a variety of factors such as descent winds etc.

de facto, please explain....what is so wrong with flying at 320/.80 :rolleyes:

I just dont see the point to fly at those speeds if not to burn more fuel,high descent rates from top of descent( unless you think idle isnt the way to go),increase in cockpit noise and be so much closer to overspeeds condition.

:rolleyes:

...but gets the day over faster, and if you're close to FDP limits (ie ops normal), you at least don't have to extend/call out the suckers.

Econ Mach and 300KIAS myself :E

As for CI, 15-28, precalculated by our flight planning software. The higher value is usually for the shorter legs (1hr) vs the lower value for the longer legs (2hrs). I don't query the computer. I just punch in the numbers.

idle is the way to go, am at idle in descent at 320knots, same as at 250 knots, it is closer to over speeding yes, however should circumstances require it, i will slow down to 310 knots, that little extra margin keeps everyone happy

Shrike, obviously if your airline has an aircraft planned to fly all day,ie if you get late the last flight of the day is cancelled then yes flying higher speeds makes commercial reason,,,but passengers im sure dont quite enjoy idle descent from high level at 320 kts,quite a descent rate..and fuel burn is highly increased..
If you are early however i decrease the ci to save fuel as a mere 100kgs saved/aircraft/leg in a large fleet makes quite a saving at the end of the year:ok:

De facto,

Many of your claims are more typical of a Microsoft flightsimulator teenage boy than of an experienced airline pilot:rolleyes:

"Closer to the overspeed conditions" are you kidding me?! 320kts. is a good standard of descend speed on NG in stable air.

"uncomfortable for the passengers" My god man, you don't know what you are talking about! It has nil, zippo nada efect on pax. comfort if you transition from level to idle descend when doing it correctly and don't slam the thrust levers etc... it is called airmanship. (but wait, I see your profile does say location China...)

In my company, we do NOT have a fuel policy, we use CI35, but this is to the discretion of the commander...

Despegue, for the overspeeds,it was regarding using .80 in cruise,for the desent rate,from level 400 ,.80 is a high descent rate through the high levels..
Ci 35 aint giving you. 80/320,,,sops is another story.
What is ur issue with my location?:ugh:

Normally about 30 gives you LRC but quite often you can see that even a ci of 40 or so will be slower than LRC.

Is there a way of fooling the FMC during the set-up to determine your minimum drag Mach no. in the cruise?
I was thinking that putting in you FL and zero wind, and ci 0 might do it. Thoughts?

Despegue,
For some reason i remembered this discussion in my pc sim today..here are my notes..
1.40 min remaining,67t, FL370,M.78 eco.
I enter select M.80/320 in my pc fms and i notice 2 mins decrease in flight time,100kgs less.
Now as a poor airmanship professional i maintain my M.78 as i rather save 100 kgs than 2 mins.
At 65T my indicated speed shows 250kts, barber pole 266kts.
Now selecting M.80 i get 260kts indicated, a mere 6 kts below an overspeed.
During one hour cruise without any turbulence my speed in few occasions increased to 256 kts,which if i had M.80 i would have got into the overspeed.
Do i think the 2 mins save worth that overspeed? i think not.

Now at top of descent i select LVLCHG withm.78 initial rate 3800 ft/min during the first 3000ft then about 3400,speed at on point increase to m.798... In which case if i had M.80 selected i would have been into m.818.. Pretty close
to another overspeed....
Now the cabin rate,,,,shows 1000 ft min, now it may nit be a new NG but still
not so nice for pax,,,,we all know the target is 300..
Now if i had selected m.80 the rate would have obviously been higher..close to 4500 ft/min.
Such rate for me is just not comfortable for me so im sure for the pax neither.

So after 2 close if not overspeeds,tell me how how i would explain to my superior 2overspeeds to gain 2 mins and burn 100 kgs more.

Now please reading a few of your arrogant answers,i suggest you get on with your mighty professionalism and let us discuss our opinions without racist comments.
:ugh:

Framer,

Ci 0 is your best endurand speed in cruise and best L/D for descent.

Cost Index of 4 gives 243kts in the descent and about .76 cruise speed.

Painful I know! :{

That is not my understanding de facto.
My understanding is that ci 0 is MRC which is faster than best endurance.
Best endurance is min drag and I would like to know a way of determining what that is while I am loading up the FMC on the ground. One of the reasons I have for this is that any slower and you are 'speed unstable' as you slide down the back of the drag curve. For interest sake I would like to be able to know what it is.
At ths stage I only know that it is slower than MRC (ci 0) .
Could it be determined using the holding page?
Framer

Just a slight add on to what I said.
In my FCOM it says that on the HOLD page, down the bottom right where it says "best speed"
What I want to know is, best for what? Endurance? Avoiding a stall? Getting around the hold quickly? I imagine it is related to endurance but I would like to know if it is min drag for those conditions. ANyone know?

From the 777 Honeywell FMS Pilot's Guide

BEST SPEED (5R) -- The best speed for the holding pattern for the current altitude and conditions is displayed in 5R. The best speed represents the maximum endurance speed to provide the maximum time aloft.

My mistake, ci0 is by BOEInG MAX RANGE (min fuel burn)for cruise and MAX L/D.
Refer to boeing website...

Maybe this will answer your question:


Vmax endurance = Best glide speed/1.316
Vmax range = Best Glide Speed

Voptimum cruise = (Best Glide Speed) * 1.316

As per the FCTM, as well as the hold page, to all practical purposes the standard clean speed derivation of Vref 40 + 70 (UP speed) would be min drag or close enough. +10-20 kts probably would make no significant difference due to, as I understand these things, a very flat drag curve. Obviously any slower and flap is required so not applicable.

As the FCTM states, another consideration, is that at altitude, UP speed is less than the min manoeuver margin, so the speed would have to bumped up a bit, Vref 40 + 100 is recommended.

I suppose this can be checked if one actually ends up in the hold, select UP speed and note the engine params, then the same for best hold speed. See if there is any measurable difference.

Thanks, I am aware of the Flap40 +100 approximation. Ours says;

I am interested that you refer to a flat drag curve. Have you ever seen one for the NG? I haven't and would really like to get my hands on one.
So the best I've got now is that Vref40 +100 is close to min drag, and ci 0 = MRC. Thats ok I guess but I would like a more definate way of determining min drag (max endurance).
Cheers.

CI of 8-9 will give you a descent speed of around 249kts :{

we use cost index 13 , 14 or 15. it depends on the flight.

My wings would if you did that to me:eek:

IRISH PiLOT!
You have a big mouth for someone who was still building hours 2 years ago:rolleyes:
Yes it is an automatic controller but please have a read on how it works!!!
I was talking about m.80 in cruise and initial idle descent.in my airline if you get an overspeed,you are scheduled in for a meeting.....rather avoid that and get a fuel bonus..but i guess you wouldnt get any of the two as you are obviously a low hour f/o and fly for a low cost..
Believe im not scared of overspeed neither was i when i was flying turboprops close to its limits quite often.(cargo single pilot sa227s) but there were no qars involved nor passengers,while you were still In high school.
Overspeed IS an exceedance just like a flap overspeed...do you think its ok to select flaps 1 at 245kts?would you say its also ok having to use your speedbrakes in case you get a flap overspeed right because of your planning:ugh:
Do you write your overspeed in the techlog after landing?obviously not,you wouldnt know where to look for one.

I save time on the ground and try to get shorter routings and optimum levels to save time...not flying at m.080/320.
For your info im paid extra for flight time,true,but also for fuel saving,fuel saving gives me a nice average of 500 eur net/month.:E

Concerning your pc sim 5000 hours thing,its a childish remark for a so called pilot,by the way i never played these games...
Fly at speeds you like and ill do the same.Enjoy the overspeeds with your speed brakes at high levels while i enjoy my coffee at a fuel economic speed.:rolleyes:

Wow....I didn't realise some companies still do this.
How do you find it? Does it have any impact on your decision making re go- rounds ?