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Marcel_MPH
26th May 2004, 17:23
Hey all,
I was wondering what the standard speeds used for climb and descent are after and before passing 10000 feet.

Marcel_MPH :cool:

Young Paul
26th May 2004, 21:54
737-300/500 - it depends on the cost index, and forecast and actual winds. Above 10000', at about CI25, the FMC speed worked out at around 275 knots for climb and descent. At 10, it was 250 knots. At 40 it was 290-300, if I remember right. This converted to a Mach no of .73-.75 above about 28000'.

Below 10000, if I remember right, the FMC defaulted to 240 knots, so that a VNAV PATH speed excursion of +10 knots on the target speed would not result in a violation of the speed restriction of 250 knots below 10000' in US airspace.

If you wanted to fly without FMC direction, 250/280/M.74 would work out just fine.

I think most aircraft types have a cost index which affects flight management speeds.

Marcel_MPH
26th May 2004, 23:53
Young Paul,

I was wondering about the 240 knots speed restriction set by the FMC but your explanation sounds very logical. During the descent it's quite hard keeping the speed exactly on 250 knots (except when flying on the LVL Change mode, 737-600/900).

Next questions which comes up is how the CI can be specified and how it can affect flight management speeds?

Marcel_MPH :cool:

FlapsOne
27th May 2004, 11:28
From the Airbus FCOM Vol 1

COST INDEX (CI)

CI is the ratio of flight time cost (CT) to fuel cost (CF).

CI = CT/CF KG/MIN or 100 LB/H

The cost index is used to compute the best economic speed and Mach to be flown considering the ratio between the flight time cost and the fuel cost.

CI = 0 Corresponds to minimum fuel consumption (max range).
CI = 999 Corresponds to minimum time.

Rgds

ZK-EBC
27th May 2004, 13:26
The rising cost of jet fuel seems to be a big issue with airlines at the moment. Could any of you drivers comment on whether airlines have changed the CI's they use as a result? Also out of interest what CI has your airline been using and in what situations do you change it. ie shorthaul vs longhaul.
thanks

Marcel_MPH
28th May 2004, 10:20
Flapsone,
thanks for your explanation. Still want to know if it's possible to use a slightly lower CI to minimise the fuel consumption a little, like it's possible to make a derated take-off with a reduced N1 setting.

Marcel_MPH :cool: