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Guest stevepow

Pmdg 737ng Descent procedures

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Ok its been a while since I have flown been very busy. I had to start whipping out all the books I used to read so that i could Catch up. Here is my question What is the correct descent rate and speed for a southwest 737-700 and 800. I already know that if i were flying on line all i would have to do to get the correct descent rate to to get to my next target would be to take the current alt and target and multiply it by 3. now that's fine but the problem is i don't fly online i fly with the atc built into the simulator so they give me no time to do all that and it would never make sense. Any way Some people have told me to use that rule for the decent rate and just leave the engines at Idle, Is this true or is there a a decent speed that i should be following.Thank youSteve Pow

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If I'm not on a VNAV descent profile (which quite often I am) and I'm using +VFPS rate for some reason to reach a specified waypoint, then I make use of the handy green arc quite a lot. Dial in a rate that gets you to the green arc. The arc is your friend!

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If I'm not on a VNAV descent profile (which quite often I am) and I'm using +VFPS rate for some reason to reach a specified waypoint, then I make use of the handy green arc quite a lot. Dial in a rate that gets you to the green arc. The arc is your friend!
I dont mean to sound like a beginner but could you tell me what ark your talking about and how do i use it. i never use vnave for descent because it is hard to use if your using the ATC with in the sim. The last time i used it , it dropped to a descent rat of 6000 and i know there is no way a plane descends 6000 feet per minute

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From my limited knowlege, a descent rate of between 800 fpm and 1000 fpm is the industry standard, barring any other compelling reasons for a steeper approach.Regards Tony Selario

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From my limited knowlege, a descent rate of between 800 fpm and 1000 fpm is the industry standard, barring any other compelling reasons for a steeper approach.Regards Tony Selario
Well, I had the chance to fly in the jumpseat in two flights LEMD-MDPC-LEMD, with an A330-200, and the descent in managed mode (something similar to VNAV) was about -2000/-2500 fpm.When the ac is close to the point of descent, pilots (at least in the ac i flew)) , notice to the controllers that they are ready for descent. This can be afirmative or wait a little longer. Even in last leg of descent , tower allowed to change the STAR (changed runway 33R to 33L, which is close to the terminal) and the pilot input a open descent with 320 KTS at 7500 ft and the angle reached -5

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I believe it's difficult to give any exact number but I once asked the same question to a pilot, his answer was that normally it would be 2000-2500 fpm at high altitudes and around 1000 fpm below 10000 feet. This is of course unless ATC instructs otherwise. Descend at a higher rate and you will notice that your speed will increase. Generally the 737 descent management is quite good if you set your constraints properly. The figures will be close to ones I mentioned above.

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From my limited knowlege, a descent rate of between 800 fpm and 1000 fpm is the industry standard, barring any other compelling reasons for a steeper approach.Regards Tony Selario
We barely descend at 800-1000 fpm in the 737. more like 2000 is the least you usually see in the descent

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There is no right or wrong rate of descent, it depends on so many factors (wind, clearance etc...). Generally speaking (apart from when following the ILS), ATC will expect a minimum of 500fpm. I agree that -6000fpm is excessive, but it's not uncommon when starting an idle descent from something like FL370 to see a descent rate of -3000fpm.In the real world, the first part of the descent will normally be flown using VNAV. Scenario 1: Before reaching the top of descent (TOD), ATC give you clearance to descend to FLXXX "at your discreation". The first thing you would do is enter the new ALT in the MCP. If you want to smooth the transition from cruise to an idle profile, you can select "DES NOW" on the FMC, and the aircraft will descend at only 1000fpm, until it intercepts the idle profile (i.e. the magenta diamond on the DPI is centred).If you want to transition from cruise straight to an idle descent, check that VNAV is selected on the MCP and do nothing. As the A/C intercepts the idle profile, VNAV will automatically change to VNAV PTH and the aircraft will descend with the engines at idle. The Autothrottle will apply power as necessary if the aircraft drifts below profile. Scenario 2: ATC issue issue a late descent clearance and you have already passed the TOD.In this instance you have two options.1) Descend using FLCH with the speedbrakes extended or modify the speed on the MCP to regain the profile.2) Descend in VNAV. If you're significantly above the descent path, then the aircraft will descsnd at IDLE in VNAV SPD. You could modify the speed using SPD INV (speed intervene) if fitted, or use speedbrakes, or both to regain the profile.Regards,Martin Neep

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now that's fine but the problem is i don't fly online i fly with the atc built into the simulator so they give me no time to do all that and it would never make sense. Any way Some people have told me to use that rule for the decent rate and just leave the engines at Idle, Is this true or is there a a decent speed that i should be following.
It is a matter of simple geometry, if you attempt to lose a lot of altitude within a relatively short horizontal distance you end up with huge and unrealistic descent rates (> 2500 fpm) and likely overspeed conditions. In real world (at least in the USA) ATC often brings you down in successive steps (so called "step downs") so you have plenty of time/space to descend gradually. In fact such extended step-down descents are not very good from fuel standpoint therefore they invented something called CDA but it hasn't reached operational maturity quite yet.

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In fact such extended step-down descents are not very good from fuel standpoint therefore they invented something called CDA but it hasn't reached operational maturity quite yet.
CDA = Constant Descent Approach.
In fact such extended step-down descents are not very good from fuel standpoint
And not very good for noise reduction too.

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There is no right or wrong rate of descent, it depends on so many factors (wind, clearance etc...). Generally speaking (apart from when following the ILS), ATC will expect a minimum of 500fpm. I agree that -6000fpm is excessive, but it's not uncommon when starting an idle descent from something like FL370 to see a descent rate of -3000fpm.In the real world, the first part of the descent will normally be flown using VNAV. Scenario 1: Before reaching the top of descent (TOD), ATC give you clearance to descend to FLXXX "at your discreation". The first thing you would do is enter the new ALT in the MCP. If you want to smooth the transition from cruise to an idle profile, you can select "DES NOW" on the FMC, and the aircraft will descend at only 1000fpm, until it intercepts the idle profile (i.e. the magenta diamond on the DPI is centred).If you want to transition from cruise straight to an idle descent, check that VNAV is selected on the MCP and do nothing. As the A/C intercepts the idle profile, VNAV will automatically change to VNAV PTH and the aircraft will descend with the engines at idle. The Autothrottle will apply power as necessary if the aircraft drifts below profile. Scenario 2: ATC issue issue a late descent clearance and you have already passed the TOD.In this instance you have two options.1) Descend using FLCH with the speedbrakes extended or modify the speed on the MCP to regain the profile.2) Descend in VNAV. If you're significantly above the descent path, then the aircraft will descsnd at IDLE in VNAV SPD. You could modify the speed using SPD INV (speed intervene) if fitted, or use speedbrakes, or both to regain the profile.Regards,Martin Neep
Thank you very much for the reply. This is the thing I don't fly online. I tried about 2 years ago and I had a bad experience one of the ATC guys started yelling at me telling me that i did not know what i was doing i told him that i was new and still learning and he told me then i should not be flying online so i disconnected and never tried it again. Its a shame though because i know that i would eventually get to know it. But when you meet people like that who forget that it is only a flight Sim it just takes the fun out of it. Anyway sorry to go off track but that's why i only fly with the Built in ATC. So let me give you an example and maybe you could tell me what i can do. Last flight i was flying I was at FL290 ATC told me to turn left heading 215 and descend to FL190 so i set my speed to 250 knots which put it to an idle state and set the vertical speed to 2500. Now let me ask you what would you do in a situation like that. remember i don't fly online so i cant set the FMC for a decent because it just wont work like that for me If the build in ATC keeps giving me headings and descents. Its extremely frustrating because sometimes im fling to fast and overshoot the airport sometimes im going too slow and it take 30 minutes more then the flight should take. I want to learn the right way at least for the Sim And willing to learn from someone that want to teach me. Anyway thank you and your comments are well appreciated

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Last flight i was flying I was at FL290 ATC told me to turn left heading 215 and descend to FL190 so i set my speed to 250 knots which put it to an idle state and set the vertical speed to 2500. Now let me ask you what would you do in a situation like that.
It's hard for me to say what I would do in this situation without knowing exactly what arrival you are following. I've also tried using the ATC facility in FSX and it's not very realistic. It will vector you miles away from a sensible approach. There is also no need to slow to 250KIAS so early. Select 19000 on the MCP and then press FLCH. Your current speed will appear in the SPD window and the aircraft will descend at idle. You can select 250KIAS at something like FL120, 2000ft will give you enough room to slow from 300KIAS to 250KIAS by FL100.

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so i set my speed to 250 knots which put it to an idle state and set the vertical speed to 2500.
You should never use VS to descend from FL290 to FL190. You have not speed protection in that case. VS must be only used in soft and short descents or climbs. Better use FLCH and select the speed you prefer...and wait for the green arc to appear. The higher you are, the higher the speed to select. Start with 300-290 kts between FL310 and FL210, later 270-260 kts between FL210 and FL120, and 250 kts to FL100.

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You should never use VS to descend from FL290 to FL190. You have not speed protection in that case. VS must be only used in soft and short descents or climbs. Better use FLCH and select the speed you prefer...and wait for the green arc to appear. The higher you are, the higher the speed to select. Start with 300-290 kts between FL310 and FL210, later 270-260 kts between FL210 and FL120, and 250 kts to FL100.
From my experience in the real world, FLCH descents are rarely used unless you have to drop it like it's hot. Because of turbulence, wind changes with altitude, etc., airplanes tend to "chase" a speed, resulting in some (auto)pilot induced oscillations. VS descents are less prone to this and therefore used more. In the sim, this isn't as prevalent, so it's not a bad idea to use FLCH for descents.Another reason - FLCH will give you the highest rate of descent for your current airspeed, since it commands idle thrust. Most times, you reall don't want this, as it will get you to your altitude much earlier than desired, causing you to have to level off at a lower altitude, burning more gas. The goal is a constant descent to the airport, and although the ideal is to do it from idle at altitude, a slower VS descent with a little power is better than making lots of steep step-downs.A good rule of thumb is to keep your altitude at a third of your distance from destination (Cruising @ FL390? Start your descent 115-120NM away). By keeping an eye on this ratio as you descend, you can adjust the VS accordingly. Really, it's more of a guess and check thing anyway.Now, all that said, I'd take a VNAV path descent anyday if possible, especially when there are altitude constraints involved, but when that isn't possible, the 3-1 rule with guess and check works great.Jonathan

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From my experience in the real world, FLCH descents are rarely used unless you have to drop it like it's hot. Because of turbulence, wind changes with altitude, etc., airplanes tend to "chase" a speed, resulting in some (auto)pilot induced oscillations. VS descents are less prone to this and therefore used more. In the sim, this isn't as prevalent, so it's not a bad idea to use FLCH for descents.
I don't know what aircraft you're referring to, but in the B73NG there is absolutely nothing wrong with using FLCH! Most operators would NOT recommend the use of V/S for the whole of the descent due to reasons already mentioned.
Another reason - FLCH will give you the highest rate of descent for your current airspeed, since it commands idle thrust. Most times, you reall don't want this, as it will get you to your altitude much earlier than desired, causing you to have to level off at a lower altitude, burning more gas. The goal is a constant descent to the airport, and although the ideal is to do it from idle at altitude, a slower VS descent with a little power is better than making lots of steep step-downs.
I'm sorry, but I disagree. You will obtain the most fuel efficiency if you perform an IDLE descent. If you're having to descend with power on, then you have not calculated the TOD correctly, effectively starting down too early! I would only recommend the use of V/S during the approach. It can be very useful for maintaining a CDA (constand descent approach).

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