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Cost index end Max range on Airbus

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Cost index end Max range on Airbus

Old 10th Apr 2008, 20:52
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Cost index end Max range on Airbus

Dear all.
as far as I remember from my ATPL study, setting in the FMC a cost index 0 means to fly at the maximum range speed.

My doubt is: does the FMGS correct that speed for the actual wind ?

Thanks
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Old 10th Apr 2008, 22:46
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CI 0 is indeed supposed to give you max range (not the same as LRC, by the way)

And yes,the FMGC does adjust for wind, At low cost indices, if the no-wind mach is a hypothetical .76, a 100kt headwind would result in .78 or so, while a 100kt tailwind will give you .74.
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Old 11th Apr 2008, 09:09
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Do not forget to fill in the forecast wind at different levels and descent phase according FCOM and FCTM.
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Old 13th Apr 2008, 11:10
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At CI 0, the speed drops close to Green Dot Sp which is the best endurance speed and not the best range speed.
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Old 30th Oct 2011, 02:24
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what' the difference between endurance and range ?
to me, a better endurance implies a greater range . right ?
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Old 30th Oct 2011, 03:26
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No, endurance gives you maximum airborne time while max range gives you the greatest distance covered.
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Old 30th Oct 2011, 03:31
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Range is Best Miles per Gallon or Nautical Miles per KG.
Endurance is minimum fuel flow (Time aloft)

As a hypothetical example:
Endurance Speed 200 Knots at 1000 kg per hour.

Range 220 Knots at 1050 kg per hour.
by travelling 10% faster fuel flow is increased by 5% so less fuel for the trip (assuming nil wind) but will run out of fuel sooner.

W1
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Old 30th Oct 2011, 10:13
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FCOM PRO.NOR.SRP.01.50 :

Cost Index for Long-Range Cruise

The flight crew can use the table below to find an approximate Cost Index value that is calculated for cruise at long-range cruise speed. This value is valid for CRZ FL = OPT ALT 10000ft.


AIRCRAFT..........................ENGINE..........................CILRC
............................................................ ......kg/min.........100lb/h

....................................CFM 56-5-B4..........25kg/min........35lb/h
A318/A319/A320/A321....CFM 56-5-B6/B7.....30kg/min........40lb/h
....................................CFM 56-5-B8/B9.....15kg/min........20lb/h
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Old 30th Oct 2011, 14:26
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Casper

CI zero does not give a speed close to green dot speed (that would be best endurance). It gives max range speed, which happens to be quite faster than green dot.

Pilot's wings

If you want to stay in the air as long as possible (patroling, holding, search and rescue...) then fly max endurance. If you wanto to cover as many miles as possible then fly maximum range.

Max range speed is faster than max endurance speed.
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