Simviation Forum - Decent...

Apr 19^th, 2010 at 7:55am

JakesF14 Offline
Colonel
Blistering Barnacles!
South Africa

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Posts: 1866

After a BIG miscalculation last night, resulting in a rapid decent, I was wondering what is the real life decent procedure in terms of your distance from your destination?

I've had this scenario:

Flying a 737-800 at 31 000ft from Cape Town to Mauritius (a weird thing happened - I ran out of fuel).
Anyway, I started to decent at 65nm before reaching Mauritius Int'l. But my decent rate was too small.

What is the correct decent rate,and where can I find more info?

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Reply #1 - Apr 19^th, 2010 at 8:25am

Brett_Henderson Offline
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EVERY OUTER MARKER SHOULD
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There's no set answer for that scenario..

But as a general rule, you can use the standard altitude/distance ratio... 3,000ft per 10nm.

Your actual descent rate (vertical speed) will vary depending on weight, and will vary all throughout the descent, as you keep trying to keep it at 3,000ft per 10nm.

IDEALLY, you'd do the whole descent at best-glide speed, but that's not realistic.. and the 3,000ft per 10nm is based around a descent where power is available, if needed.

Since you don't have the real-world help of ATC and a bunch of engineers on the ground helping you when you run out of fuel.. it's gonna take some quick thinking on your part.

If I were at FL310 and 65nm from an airport, in a powerless 737, I'd note that I'm WELL withing gliding distance.. so I'd start some gentle S-turns toward that airport.. all the while trying to stay on the safe side of 3,000ft/10nm

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Reply #2 - Apr 19^th, 2010 at 8:28am

Brett_Henderson Offline
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OH ! .. and don't forget winds aloft... Wink

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Reply #3 - Apr 19^th, 2010 at 8:54am

JakesF14 Offline
Colonel
Blistering Barnacles!
South Africa

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Thank you Brett.. I guess I'll have to practise that!! Actually I ran out of fuel with just less 1000NM still to go. But i quickly refuel (and I think it is an error on the POSKY 737-800, as the range of the 737-800 is over 3300nm, and the distance between FACT and FIMP is 2440nm.)

But I am learning...... Wink

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Reply #4 - Apr 19^th, 2010 at 9:30am

olderndirt Offline
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Flying is PFM
Rochester, WA

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Don't forget to factor in anything weather-related - holding, missed approach and/or having to go to an alternate.

THIS IS NOT A PANAM CLIPPER

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Reply #5 - Apr 19^th, 2010 at 10:15am

JakesF14 Offline
Colonel
Blistering Barnacles!
South Africa

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Posts: 1866

olderndirt wrote on Apr 19^th, 2010 at 9:30am:

Don't forget to factor in anything weather-related - holding, missed approach and/or having to go to an alternate.

Going to an alternate.. yeah I forgot about that!! A good thing I am not an airline pilot....yet!

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Reply #6 - Apr 19^th, 2010 at 5:16pm

-Crossfire- Offline
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Northern Canada

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I tend to use the 3:1 ration rule, which works well for most larger aircraft.

Cruise altitude - field elevation x 3 = natuical miles
If you are at 30,000 feet, and your desination airport is at 2,000 feet, that is 28,000 feet of altitude to lose. 28,000 feet expressed in thousands is 28. 28 x 3 = 84. Begin the decent 84 miles back.

Now what should you use for rate of decent? Take your ground speed, add a zero, and divide by 2. Let's say you're grounding 400 knots, 4000/2=2000. Start the decent at 2000 ft./minute.

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Reply #7 - Apr 20^th, 2010 at 12:00pm