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airlinerpilot

What speed do you descend at in a commerical airliner?

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I was just wondering, what is the recommended speed for a descent from cruise altitude? Say I am flying an airliner at 35,000ft and I am told by ATC to descend, what is the most realistic speed?

Currently I set my IAS to 250kts and allow the aircraft to slowly loose speed during the descent. I very rarely fly above 250kts at 10,000ft or below unless I am granted permission.

 

Also, what is the recommended vertical speed? I set mine to -1800. And when below 10,000ft, judging on the distance from the airport I set it to -800. Any tips? Thank you kindly! ^_^

 

 

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Are you using payware AC or default? Payware will usually track the vnav speeds/descent rates for you.

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For any default or 3rd party freeware airliner I do pretty much the same as you describe.  I generally wait until under FL190 to set the descent speed to 250kts.  From FL350 down to FL200 it's usually about 280Kts.  VS is set to 1800 and depending on how far out from destination I am, it stays there.

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I usually descend at a speed of 250-260 kts and at a vs of -1400 from cruise. Gets me down in time for my crossing restriction and I can drop speed off without using the speed brake...Most of the time!

 

I don't fly online though, I use Radar Contact.

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Most commercial aircraft descend at a predetermined speed which is calculated by its flight management computer. The speed is determined based on a number of factors, but most prominently the cost index that is used (a measure of time related cost versus fuel related cost) and the aircraft's gross weight. For a Boeing 777, this is usually about 260 to 270 knots indicated, depending on the conditions. All descents are flown at idle thrust for as long as possible to minimise fuel consumption, so you would fly (or let the autopilot fly) the aircraft at a descent rate that maintains the descent speed.

 

The vertical speed is a function of the aircraft's descent speed, so normally a descent isn't flown at a constant VS, as it tends to reduce as you get closer to the ground due to the aircraft slowing down. The autopilot trims the nose of the plane to maintain the set descent speed. Lower down, speed restrictions of the arrival procedure, as well as ATC assigned speeds come into play, so the descent rate is adjusted accordingly. Typical descent rates at high altitude, say above 28000 odd feet are about 2500 fpm. Lower down they reduce to around 1700 fpm, and at 10000 feet and below they drop to around 1200 to 1300 fpm.

 

Hope this info helps. :smile:

 

Regards.

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I thought IAS was a little higher on descent like between 290-330 on initial descent. I was on a jumpseat recently in 737-700 and they kept it 290 until 4000 feet and about 20 Miles out. This was in the Netherlands where around EHAM Alpha starts at 1500 feet.

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I thought IAS was a little higher on descent like between 290-330 on initial descent. I was on a jumpseat recently in 737-700 and they kept it 290 until 4000 feet and about 20 Miles out. This was in the Netherlands where around EHAM Alpha starts at 1500 feet.

 

Sounds unusual, but then again i've only experience of simming. 

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... most prominently the cost index

...

I don't think cost index is a factor when it comes to descent speed, as descends are done with the engines idling

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Wim, the cost index does actually affect the ECON descent speed. As cost index increases, the descent speed increases. Idle thrust doesn't necessarily dictate the descent speed, as a descent made at 320 knots at idle thrust, can be made just the same at 260 knots with the same thrust setting. The only difference being, you'd expect the vertical speed to be higher in the 320 knot descent and the top of descent to be closer to the destination..

 

Best regards.

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I was just wondering, what is the recommended speed for a descent from cruise altitude? Say I am flying an airliner at 35,000ft and I am told by ATC to descend, what is the most realistic speed?

 

Currently I set my IAS to 250kts and allow the aircraft to slowly loose speed during the descent. I very rarely fly above 250kts at 10,000ft or below unless I am granted permission.

 

Also, what is the recommended vertical speed? I set mine to -1800. And when below 10,000ft, judging on the distance from the airport I set it to -800. Any tips? Thank you kindly! ^_^

 

At FL350, you would be referring to Mach no., not IAS.  So if you're cruising at, say, .78, maintain that speed while descending.  Typically, you aim for a 300 ft. per mile descent, so your vertical speed needs to be groundspeed x 5 (400 kts. GS x 5 = 2000 fpm).  As you pass through about FL270, look for that .78 Mach to equal 280 KIAS (or any number you choose to use, but these days most economy descents are done at about 280 kts.), and you can maintain 280 KIAS all the way until it's time to leave 10,000 ft.

 

Try this for an exercise:  be in cruise at FL350 direct to a fix that's 100 miles away; your goal is cross that fix at 10,000 and 250 KIAS.  You need to lose 25,000 ft. (rule of thumb, 3 miles per 1000), so that's 75 miles, plus give it another 10 miles as a fudge factor and room to slow from 280 to 250, so start descent 85 miles from the fix.  Use whatever power setting it takes to maintain desired airspeed and vertical speed.

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I was just wondering, what is the recommended speed for a descent from cruise altitude? Say I am flying an airliner at 35,000ft and I am told by ATC to descend, what is the most realistic speed?

 

Currently I set my IAS to 250kts and allow the aircraft to slowly loose speed during the descent. I very rarely fly above 250kts at 10,000ft or below unless I am granted permission.

 

Also, what is the recommended vertical speed? I set mine to -1800. And when below 10,000ft, judging on the distance from the airport I set it to -800. Any tips? Thank you kindly! ^_^

Are you flying something with an FMC? If you have one, it would figure that out for you, and then all you would have to do in most cases is set the altitude you want to descend to and click on the VNAV. Of course, if, during the descent, the air traffic controller starts giving you speed restrictions, that goes out the window, and then you would use FLCH to maintain that speed.

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About 1500 to 2000 fpm does the trick. If I need to slow down, there'll be less. If Radar Contact imposes a crossing restriction, there'll be more (and some panic).

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