Simviation Forums

When an airliner, let's say, flying at 32,000 feet is directed to descend to a lower altitude, let's say, 22,000 feet as it approaches it's destination, is there any time factor that the aircraft has to get to the new assigned altitude? Also when at cruising altitude, how far out does the aircraft have to be to start making it's descent?

Having flown recently in the jump seat of a 737-800 and a Dash 8-Q400 I can tell you that the 737 started a decent from 36,000 feet 60 miles out from the destination airport and the Dash started to descend from 26,000 feet 60 miles out. The only difference I saw was the 737 descent was direct to the airport, were as the Dash descended to 6000 feet and then flew the rest of the way in at that altitude. The Dash finished it's descent about 20 miles out. Both flights were to and from the same airports.

Matt

Rate of descent (as in vertical speed), can't really be a target, but more a reference as in, there are safe/comfortable limits.

I've never flown big airplanes, but I imagine it's similar to the small stuff. You have decent airspeed targets, and then adjust for the winds. For example: A descent that starts at FL330, could very well have extreme head/tailwinds to deal with.

An FMS will take care of all the adjustments.. or a crew can just try to keep the altitude/distance ratio near 3:1 (3,000 feet for every 10 miles out)..

**this is just an educated guess**

Edit:  Ooops.. forgot the original question 

But I'd imagine it's similar.. i.e.. target airspeeds and adjustments for winds.

Your average mid-sized jetliner on a medium route is probably going to start it's decent from the flight levels anywhere between 50 and 70 nautical miles out.

The smaller stuff....maybe 20 nautical miles out....30 if you want to have a really minimal VS.

Planes delivering skydivers.......just pop out full flaps, prop reverse, gear, etc and dive toward the airport from 2 miles out, you'll be fine. 
http://www.youtube.com/watch?v=AD1xBMth ... re=related

what is the abbreviation mn? is that minutes?

From my past experiences I can tell that airliners normally start their decent 30 minutes before touchdown. As Brett said, probably depending on the circumstances. At some places the decent goes in steps, while flying into Brussels, planes use a more steady decent pattern to save fuel.

As far as the decent rate goes, Tunisian pilots seem to start the decent at a faster rate than Belgian pilots do. I could really tell the difference... my stomach felt a difference... lol

I never flew the tubes/turbo's so I would not know what their decent procedures happens to be but the following worked well so far for me in the smaller SEP's.

Always been using this general formula & works well for me:

1) Take your cruising Altitude eg. 7000 feet. Take your airport's altitude eg. 1000 feet. That leaves you with 6000 feet. Take the 6 and multiply such with the factor 4. That gives you about 20 NM to start your decent.

2) To establish your rate of decent, take your decent airspeed eg. 85 knots & devide that by 2 to get 42.5 Round it off to get 43, add the factor 0 to get 430.

That gives you a sweet 430 f/m decent rate @ 85 knots starting 20 NM out.

Saves fuel, avoid rapid corrections & keeps the coffee in the cup