Controlling descent rate

Still learning the ropes here guys so please be gentle.

Scenario: Flying a 787-800 at FL35 and at 0.85M I want to start making my descent of 1500ft/s to below 10,000 for approach.

How do I control my speed from 320 to below 250 with a high descent?

Have been using a mix of flight spoilers and flaps but is all abit of a fumble especially with high descent rates (>2000ft/s)

Please could someone talk me through a controlled descent from cruise to approach.

Many thanks in advance

Lloyd

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From cruise down to 10,000 it is advisable to use autopilot to control your speed and rate of descent. Set an altitude of 11,000 and your desires V/S (vertical speed) and once you’ve reached 11,000 you can procede beneath 10,000 after verifying your speed is below 250 knots. To calculate your descent (roughly).

When you should start your descent:

  1. Find the altitude you need to lose, e.g 28,000 feet.

  2. Remove the last 3 digits, multiply by 3 and add 5 (28,000 -> 28, 28 * 3 = 84, 84 + 5 = 89) and that is how many NM (Nautical Miles) out you should start your descent at.

To calculate descent vertical speed:

  1. Multiply your GS (Ground Speed) by 5, e.g if I’m travelling at 300 knots GS, 300 * 5 = 1500

  2. Descend at this rate (in the example, 1500 feet per minute)

  3. Recorrect every 10 mins as GS changes (even at a constant airspeed GS changes as winds, temperature, and air pressure change)

It takes time to perfect but eventually you’ll have no difficulty descending

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Hey @NoK_Su_Kow, just make sure in autopilot your speed is set to 250, or 0% throttle, and open to spoilers to flight until you reach 250 knots! Or, you could have a shallower approach at -1000FPM, and level out at FL105 if you are above 250 knots, then decend to you desired altitude when you reach your approach speed.

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You answered before me. ;-;

Thanks guys! …been using AP for my speed and with the throttle at 0% my speed is increasing; kinda of makes sense but even with flight spoilers my speed is so slow at getting down to <250 that I have to decrease descent rate to an unplanned rate.

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I didn’t get any of those numbered steps…

Whats your decent rate at? And how much speed do you lose every 10 seconds?

That probably means you’re descending too late, which means you will need to descend faster which prevents you losing speed easily.

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Will have to go back into the sim to work that out but its around 5knots I think.

Once you’re out of mach flight levels don’t let your speed exceed 290 knots. 300+ is unnecessary and will cause issues.

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I think your right and need to plan my descents much earlier… so could you talk me through a typical descent with DTG and descent rate please?

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@Insertusernamehere just seen your edited first post… brilliant thanks!

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And always level off above 10k to slow down before you descend further. This will help to avoid violations…

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Well, now I know how to start descending correctly. :)

I’m going to bookmark this just in case I forget.

What I do, is I find out how far out I need to descend (multiply altitude by 3 and then divide by 1,000) and then add 5-10 miles to that. So I cruise at Mach .85, so then at that 5-10 miles before I start my descent I slow down to Mach .65 (240 mph) and descend at 2,000ft vertical speed. With my spoilers set to flight. This has always worked for me! Hope Thai helps!

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I used to start my descents at the end and I never had enough to land but I decided to make my descents much earlier and it is very good for the newcomers because it is not easy to land, it is the hardest part of the flight for some like me.

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So far as proper descent rate is determined …my view is that since most irl airline pilots average about 20-30 miles to descend from a cruising altitude of around FL300+…then in order to “gracefully” descend it would be more advantageous to start out at between 125 - 150 miles from your destination airport at a descent rate of 1200-1500 fpm in order to prepare properly and have a little cushion to arrive so that you are around 15K or less when you first contact the approach controller at between 50-60 miles out …and further more if you wish to customize your descent to your own personal taste…you can simply divide your cruising altitude by varying fpm factors to determine how many minutes you want to take to descend for landing !!!

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Slow down before you decend and if needed use flight spoilers

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@Noah_Simonich, please refrain from commenting suggestions that have already been addressed by other users.

as you also giving calculation example of -1500 fpm, at what GS speed this descend should be?