Question about procedure to slow down when descending

I’m sorry for this noob question but…

What is the proper IRL slowing-down procedure for airliners when they’ve reached TOD to slow down from cruise speed e.g. from M 0.81 to below 250 kts? Is there such a thing as step braking procedures to reach certain speeds at certain altitudes when descending as you’re nearing your destination? I know that abruptly slowing down is not a good thing mid air (passengers will not like it lol).

Or has this question been answered somewhere in the forum in a differently worded question as such that I missed it? :D

*Two bonus questions:

  1. I’m also guessing that flaps aren’t necessary when descending even if you’re going slow, is this correct?
  2. Tower usually tells me to expedite it sometimes when I go 150-160kts through the cone during final… how fast was I supposed to go when runway is in sight??

Currently at fl360 above Paris en-route LIRA-EGLL as we speak. Any help would be appreciated, thank you!

  1. Yes, I only pull them out at around 7000 or below
  2. I usually do 180 kts when I enter the cone. Maybe 170 for narrow bodies and smaller planes.
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Many STARs will have speed restrictions at waypoints if you look them up online. When they’re absent, I do:
Cruise Speed → FL300
290 KIAS → FL200
270 KIAS → FL100
250 KIAS below 10,000 feet.

Additionally, unless you are instructed to maintain such speeds or “slowest practical speed” I suggest 170-190 KIAS when entering the cone. Otherwise, you’ll slow down the traffic around you 🙂

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@Claudio @CameronH21 Thank you so much for the input!

It’s a bit of a grey area this.

As already stated, a number of procedures have speed restrictions already published. If this is the case, follow them.

The bigger question is what happens when there aren’t any published restrictions. This is where the aircraft’s descent profile comes into play.
As part of your Simbrief OFP, you will notice the term ‘Descent Profile’. In basic terms, it tells you the speed at which you fly during different parts of the descent.

Above is the descent profile of an A321. Notice how it is divided into three numbers. These numbers correspond to three different stages of flight:

78 - this is your cruise speed, meaning Mach 0.78. It is also the speed you should initially target at the top of descent.

300 - as you begin descending at constant Mach number (0.78, the first number), your indicated air speed with increase as the air around you becomes more dense. At the point at which the indicated speed reads 300KIAS, you should transition from a constant Mach number descent to a constant IAS descent. This will result in a slightly slower rate of descent and you will notice your Mach speed slows down. Hold this speed until you are approaching 10,000ft.

250 - this is the speed you should fly at below 10,000ft. Usually the aircraft would level out at around 10,500ft, known as a DECEL point, and let the speed bleed off from the 300kts to 250kts. Once you’ve slowed down to that speed, pitch down again to maintain that speed until you either have to slow down for approach or you are told to slow down by ATC.

Hope that helps.

Side note - in the real world, descents are almost always flown at ‘Flight Idle’ (a variable engine speed usually in the region of 30-40% N1). However, doing this in IF seems to require a steeper than usual descent in order to maintain the correct speed with some aircraft.

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A lot have been known and talked about in the forum regarding descend calculating, but the speed aspect during its process remained a small discussion (at least in my opinion). Just to immerse in realism™ or even when someday IF introduces passenger and cargo booking to assign along your flights these will become important. But all in all…

I think for a lot of some others (and mostly including me lol!) all these information you guys just provided are:

BOOKMARK MATERIAL!

Great stuffs guys, great stuffs!

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In relation to the question about flaps… Flaps allow the plane to remain flying (generating lift) at lower speeds, the more flap the lower the speed possible.

It doesn’t matter whether the plane is descending, climbing, or level, the flaps do their thing with lift. You could use flaps to get to a lower altitude at a closer position because they would allow a slower speed… Slow right down with flaps, then lower the nose to increase the descent rate. Watch the airspeed though as it will increase. Check the flap speed limits.

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The most economical and efficient way is to fly a so-called ´idle descend´, which means you select idle trust and regulate the speed solely by increasing and decreasing the pitch/descent rate. This is a realistic and very efficient way to descent, but requires a bit of experience (just try it out and improve according to the experiences you make!).
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Flaps are mainly used to increase lift/decrease the angle of attack during low speed flying. You will need to deploy them when the aircraft pitches up too much to maintain its current altitude/descent rate but not before you are below the maximum speed where you are allowed to deploy them (e.g. on the Airbus A320family and A350 you will find a placard in the flight deck with those speeds).
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A classic intercept speed would be something around 200-210kts, reducing to 180 at 8 miles and so on.
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If you want to learn more, please consider to have a look at the fantastic IF guide I linked below, which does a lot better job explaining then I do!

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Taking about speed when on final, it really depends on the aircraft. Some planes (eg. 787) have trouble slowing down without high flaps settings, so you will need to slow to 180 or so before intercepting the glideslope so you are below the flaps 20 limit. Otherwise you have to take gear out early.

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