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Thread: Start of Descent Point

  1. #1
    Join Date
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    Default Start of Descent Point

    Hi,
    My newer user aircraft are great to fly but they don't slow very quickly on descent. I usually start my descent about 130 miles out at 1500 fpm, but find myself sometimes over 280 kts which pushes the flaps limit. I can increase the parasitic drag but that's artificial. How do you handle aircraft that don't lose speed on descent.Should I start my descent sooner? I'm using both Simmer's Sky Boeing aircraft and CLS Airbus aircraft. Thanks for any feedback.

  2. #2
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    Quote Originally Posted by Honus View Post
    I usually start my descent about 130 miles out at 1500 fpm
    There's no initial and no target altitude in your "formula", so it's doomed to be wrong.

    The rule of thumb is 3 Nm travelled per 1000ft of descent.
    But for some types of jets I found 4 to 1 more realistic.
    Take notes of your mistakes, and apply the corrections in yr next flight.

    Wim

  3. #3
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    How much are you reducing power to start the descent? You can come all the way back to flight idle. Also, you could deploy spoilers as they sometimes do on real aircraft.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  4. #4

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    Try descending at cruise Mach at 2500 fpm till reaching 300 KIAS, then hold 300 KIAS / -2500 fpm to about 13000 MSL, then decel to 240 KIAS at 1500 fpm to 5000 MSL. Make sure you are at or below 250 KIAS approaching 10,000 MSL before going lower.

    Depends on aircraft type, airport pattern altitude, STAR restrictions, etc but for your purposes this is realistic.

    3x cruise altitude is the starting point. Remember, at a constant rate of descent and constant INDICATED airspeed, your flight path STEEPENS because your true airspeed/groundspeed is decreasing during the descent.
    Last edited by mikeandpatty; 02-26-2021 at 06:01 PM.

  5. #5
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    In my Jet flights, normally IFR, I would never wait for ATC to tell me to start my descent. I would use 150 miles out as a starting point and request descents in 10,000 foot chunks. Usually by the time I hit 18-20k feet, I'm about 55-60 miles out and ATC has taken over control of my descent towards the airport. Use spoilers, momentarily, to keep your aircraft from gaining too much speed.
    Mr Zippy Sent from my keyboard using "Whackamole", NudgeAKey + 2 Fingers

    No flight Sim installed until I get a new computer.

  6. #6
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    Take less fuel with you.
    Make sure you have no more then 20-25% fuel remaining when starting descent.

    Don't use flaps on descent. (and definitely no flaps at 280kt)

  7. #7
    Join Date
    Jul 2014
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    Florida
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    Default Start of Descent Point

    If you’re using classic jets with no FMC and little automation, you’ll have to figure which of the above rules of thumb work best. If you’re using a modern jet with FMC and VNAV/FLCH, the automation will do most of the work. But it will do (speeds, altitudes)what you’ve programmed it to. If it’s not doing what you want, check what you’ve told it to do.

    Larger planes have difficulty slowing going downhill like anything else. If necessary, slow first then descend at your target speed.

    Sent from my iPhone using Tapatalk
    Last edited by Palmored; 03-01-2021 at 08:57 PM.

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