carlwag

It is desireable to be at 30,000 or higher until just 100 nautical miles from your destination, but when coming from the southeast US into Chicago, that is not allowed. The air traffic controllers routinely descend the northbound airplanes to cross abeam Indianapolis at about 26,000 feet or so. This keeps them under the east and west traffic that passes over Indy at 28,000 and higher. It is quite a waste of fuel for all of the ORD traffic to be down that low, but they do not seem to be willing to allow the ORD traffic to stay up higher. Often the controllers will assign speeds of 320 knots or greater, which is really a waste of fuel, as jet airliners are generally much more fuel efficient at speeds of 250 to 280.

Top Bug

BA Pilot, in theory best L/D descent will generate max fuel savings but in the real world it will NOT. A 250 KT descent will get you off path vectors so faster traffic can pass you and hence you will burn more fuel. There are not too many airport enviornments that you can descend at 250 KTS , especially the UK with the CDA profiles in use. A lot of of airlines are using a VNAV profile descent using an "econ" setting for the control index in the FMC. Fuel economy is dynamic and requires constant monitoring to achieve "real" fuel savings. You do 250 at KLAX, I will do 290 and I will beat you to the hotel every time and save more gas than you will. Now lose the attitude speed bird.

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tflyer70

Here's another rule of thumb that I was able to prover time and time again for those who opted to say "Im doing X miles a minute...."

That was too much

If you use the descent profile of 3 times your altitude to determine how far you want to start out (this provides a rudimentary 3 degree slope, depending on field elevation) i.e 25,000 ft=75NM out to begin descent, and....

Use 6 times your ground speed to determing your rate of descent (i.e. groundspeed is 300= 1800 FPM)

If you have a high groundspeed you may want to use a 4:1 ratio, or 4 times altitude, but this doesnt do much for fuel savings. When I flew cargo we did a 2:1 which meant that our descent rate had to be picked up to about 9 times the groundspeed.

Just a thought

Ewfflyer

Darwint: I fly from Muncie, so feel free to come visit over here for any in person questions.

I'm suprised none of the guys hit on this either:

There's an arrival called the "Clang Five" into IND. It has turbojet traffic crossing 17nm(PENDS) SW of Muncie VOR @ 11,000. So he's probably seeing traffic around the 12,000' range in the Anderson area.

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698jet

It also deponds on the aera like florida to teb you some times start dowm 300miles out . these is due to the north east traffic but most times 3 to 1 work out fine.

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NightIP

That's good for zero wind, but I typically have used (Groundspeed)*5 for the descent rate. Works well for a 3 degree slope.