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Descending rate.

Sico2 Guest

I still don't know how to choose proper descent rate since I'm using my FS2004 for manual approaches. I've just been flying from London Gatwick to Philadelphia USA. And let us say, I'm cruising around 440knots on a FL370, and the runway is 123nm north away from me. The atc tells me to start to descent to a FL280, and then when I reach the level, it'll tell me to descent further. Allright, everything nice, but what if I'd like to do manual approach. What descent ratio should I choose? with speed of 440knts, ona fl370 and an airport away from me north 123nm? If I'm going to descend too fast (let us say 2000-1800ft/min) I'll end up on a (let's say 6000ft) level still appr.30nm away from airport and probably using too much speed brakes to slow down the aircraft, but if I'm going to descent too slow (1000-1300ft/min) I'll end up let us say 10000ft over the airport 5nm miles from it, and then I'll have to descent very quickly using loads of brakes and even cause my passangers and flight attendants to vomit all over the plane because of the -G. Or maybe I'll end up going around and overshooting the airport!
Can anyone please help me and tell how to choose the correct ratio of descent, what do I have to count, and how to count it properly in the future with many types of aircrafts, on differents flight levels and approach speeds? Any physics involved like V (velocity)=S (road) / T(time)?

9 Responses

Pro Member First Officer
beerbadger First Officer

Ask CRJCapt he knows his stuff 🙂

Pro Member Chief Captain
Jonathan (99jolegg) Chief Captain

I personally use this method:

1. top of decent = 3 x (altitude - airport elavation) divided by 1000

For EGLL, 3 x (5000 - 80) / 1000
4920 x 3 / 1000 = 14.7nm

2. For the rate of decent you need to no the True Airspeed (TAS)
..... IAS X 0.02 X (Altitude / 1000) + IAS

So.... 300 x 0.02 X 5 + 300 = 330....so 330 is the true airspeed

3. FOR RATE OF DECENT, MULTIPLY TAS BY 5, i.e. 5 X 330 = 1650fpm

At 14.7 nm away from the airport, you need to decend at 1650fpm

Have a look here: https://forum.flyawaysimulation.com/forum/topic/3299/three-questions-about-landing/

Pro Member Chief Captain
CRJCapt Chief Captain

With much respect to 99Jolegg, that's all correct but too much math for me, while flying. I just multiply the altitude times 3 and descend at 1/2 my ground speed (GS).
FL370 to sea level airport GS 440 knots.

37X3 =111 Distance to start the descent.

rate=2200 FPM (initially)

This will give you a 3 degree descent gradient. As you descend, this rate can be decreased because you GS will decrease.

At 10000 ft. indicating 250 kts., your GS (and true airspeed TAS) will be approx. *290-300 kts. (zero wind)

10X3=30 Your distance to the airport when at 10000 ft.

rate=1450 or rather 1500 FPM

* 290-300 is your approx True airspeed at 10000 ft when flying 250 kts. on your airspeed indicator (KIAS) Determined by flight computer or by adding 2% increase per 1000 ft of altitude to indicated speed (KIAS). Very approximated.

Just keep your descent rate at 1/2 you GS and you will fly a 3 degree descent angle or gradient. With this rate, your distance to descend will always be 3x you altitude you want to descend.

This method accounts for head or tail winds effects that the TAS alone method, does not. 🙂

Guest

I would like to thank you all guys for the answers. I'll try that on my approaches. I'm not that good in math, so I'll try the easier way, FLx3, and then, GS/2 for ft/min.
Is this the method also used officially by pilots, or do they do the math thing or do they just use autopilot and do it by sence, I mean, using their experience (It is always about 1500-1800ft/min).

By the way, what is the proper rate of descent in real life, let us say in B757, so that the passangers won't start to feel like they weight a half of it what they used to on the ground (too fast descent, -G Wink. I've heard in commercial flights the descent rate shouldn't be higher than -2200;
-2500ft/min, depends on speed and wind I guess. And the same I think is with the climb. If you have 3000ft/min of climb, some passangers could start to have blood pressure problems or faint or similar won't they because of +G?

Pro Member Captain
Sean (SeanGa) Captain

how do you get your ATC to give you flight instructions? I'm not very experienced with FS.. tnx in advance

Guest

I usually do this by planing a flight in FS2004 (main screen, 4th button from left 'flight planner'), then choose your airports from/to, GPS or VOR navigation(either you'll be flying from A to B in the quickest possible way,or from VOR to VOR,pretty much longer way) and then choose IFR. If you give VFR you'll be cleared to take off and all what you'll get is "maintain own navigation..." blablabla... 😕 If you choose IFR, they will tell you everything what to . The only thing you'll have to do is use throttle, maintain height, and turn on approach button on short final to your airport.

Pro Member Chief Captain
CRJCapt Chief Captain

The formula I posted earlier works for Flight Simulator and real life.
In a steady state descent the aircraft only experiences 1 G. As you level off from the descent, the G amount won't rise too much, if you level off correctly. 2000-2500 FPM would be a descent rate used in real life. The max. rate depends on the aircraft or more accurately how daring the pilot wants to be to help ATC. I would say that 3500-4000 FPM would be the max. As you get within 1,000 ft. of your target altitude, you are required to descend no faster than 1,500 FPM. As for climbs, same thing. The level off rate causes the G force reduction. The rate of climb or descent is not a problem for passenger in a pressurized aircraft. It's another story in a unpressurized general aviation aircraft. 🙂

Pro Member Chief Captain
Jonathan (99jolegg) Chief Captain

All methods I have come across and tried, all amount to the roughly the same descent speed and distance from the runway, its just choosing which ever one you prefer. Theres loooads of different ways to determine your descent speed and TOD, but CRJCapt's is certainly easier. FEM has mentioned a similar one in the post above if your interested 😉

Pro Member Chief Captain
Tailhook Chief Captain

SeanGa wrote:

how do you get your ATC to give you flight instructions? I'm not very experienced with FS.. tnx in advance

I might have misread the whole thread, including the above question. If that's the case, please ignore me.

It seems to me that SeanGa wanted to know how to contact ATC in the first place. Just hit the Tilde button right beneath the Esc button and the ATC window will open. Follow the instructions.

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