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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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I don't know about how it's exactly done in real life, probably with both (VS & LVL CH) depending on the conditions and ATC. But the FS world isn't that accurate, especially in terms of winds and ATC. I find it better to use V/S when there are sudden wind direction changes. In LVL CH mode the aircraft does not maintain a nice smooth descent wtih this FS glitch. I agree with Jonathan on using VNAV as much as possible, if you insert your constraints properly or apply the 3-1 rule and everything goes fine (ATC giving you the expected runway for example) then the PMDG 737 handles it perfectly.I don't use LVL CH very much for descending but rather for climbing, that's what's VNAV climb without constraints is anyway.I like to keep my descents around 2000FPM in idle, LVL CH is prone to exceed this especially at higher altitudes.I guess it's all down to personnal preference in FS. In the real world though passenger comfort is very important and steep descents are very uncomfortable (not for all of us!)I think it was Dan Downs who said it here, "VNAV is strategic and V/S is tactical". It makes perfect sense to me.

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Is there anyone one here who still uses the atc build in the flight sim? Lol

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Is there anyone one here who still uses the atc build in the flight sim? Lol
Sure there is, at least I do. If you fly with real world charts and know how to work your way around FS ATC, it isn't that awful. :(

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Sure there is, at least I do. If you fly with real world charts and know how to work your way around FS ATC, it isn't that awful. :(
Ok so let me ask you then. How would you go about a decent from FL290 to FL190While using the built in ATC going about 330 knots

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Easy, since the built-in FS ATC doesn't care about your speed, just dial your desired altitude and in the MCP and hit the LVL CH or V/S button.Oh, and don't forget to ask for FL190 via the ATC menu.EDIT: Steve, if you use LVL CH at 330 KTS, your descent will be very steep, 280-300 KTS would be more realistic.

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Is there anyone one here who still uses the atc build in the flight sim? Lol
There are some who use. Some fly without any ATC. Some like Radar Contact - much more realistic.
How would you go about a decent from FL290 to FL190
Any method that keeps your speed within limits and gives reasonable descent rate is fine. Some like FLCH, some V/S but you have to be extra vigilant when using the latter, some use combination of both. ATC actually doesn't care how you do it unless you do something weird - either descend too fast or too slow. ATC definitely doesn't like to be surprised.

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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).
I totally agree with you regarding efficiency. What I'm talking about is real world operations though. ATC (including FS ATC) has absolutely no idea whatsoever where your calculated/ideal TOD is. Sometimes you'll be lucky and get a pilot's discretion descent, which in effect lets you fly the ideal path, but more times than not, this doesn't happen, so you'd rather make it a smooth descent. Remember, turbines burn MUCH more gas down low, so you'd rather not descend from up high (lower FF, higher TAS) really fast, only to have to fly level down low (higher FF, lower TAS). You'd rather be up high as long as possible, but if you have to descend before your ideal TOD, do it at a lower VS in order to stay higher longer.
Ok so let me ask you then. How would you go about a decent from FL290 to FL190While using the built in ATC going about 330 knots
I'd dial in FL190 in the MCP, then set a VS somewhere between 1500-2500 FPM depending on how far from the airport I am. If you're doing it without the ATC, use VNAV so you get an idle descent from the calculated TOD. As TotalBeginner has mentioned, the most efficient descent is at idle, so if you're your own ATC, why not do that!?Another consideration I didn't mention earlier that deals with the 3-1 rule is the effect of temp (read: altitude) on your true air speed. Up high, you're going much faster at the same indicated speed, so you'd need a higher VS in order to maintain a certain descent path. As you descend, your TAS drops off, so you'll need to reduce your descent rate to keep the same angle. The same consideration is made for wind...a huge headwind, descend at a slower VS, a huge tailwind, higher VS. Like I said, it ends up being a lot of guess and check that isn't much of an exact science.Jonathan

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I use this method with the PMDG model, and now that i have the IFLY, that.From high altitude, its a V/S descent. I set a descent rate of 1600ft/pm, with a mach speed of .78. When the airspeed hits 320kts indicated, i switch from mach speed to knots and maintain 320kts down to FL120, whereby ATC (Radar Contact) levels me off in preperation for the final phase of descent. This is where i back the speed off to 250kts indicated.From then on in its a "FLCH" descent, the aircraft rarely descending anything past 1500ft/pm. I Keep a careful watch on the green arc, to make sure i will level off with plenty of time to reduce speed for final approach.As ive said earlier, Radar contact likes you to be at around FL120 before reaching 40nm from the airfield in preperation for approach instructions, and the above method allows me to easily achieve that.Each to there own, as long as we achieve the same aim, to land in one piece!

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ATC actually doesn't care how you do it unless you do something weird - either descend too fast or too slow. ATC definitely doesn't like to be surprised.
Exactly.I'll put it this way:ATC expects the "norms" for your plane, which are outlined in the appendices of the 7110.65. Based on that chart, ATC expects about 4000FPM climb and descent out of the NGs in "normal" (I didn't use "standard" for a reason) weather, at median weight. How does ATC know? If you're Alaska 2 from KSEA-KDCA (a 73NG), chances are, you're probably not getting 4000FPM on the climb out of SEA. The controllers have the knowledge assume that you'll be a little slower on that climb.To make this slightly more understandable, but confusing in its own right: controllers really don't pay much attention to the numbers. They go with their experience and general understanding of the aircraft. What I mean by that is, having controlled Aircraft Type A several times before, I can expect that it will do the same when I control it today. This is where Michal's point is key. From an ATC standpoint, there is a too fast and there is a too slow.For some reason, FS Autopilots defaulted to +/-1800 VS mode for a while (do they still? I haven't flown default airliners in years). Because of that, people assumed that 1800 was the norm, and was somewhat the rule. That VS is too shallow on both ends. If you think about it, if you need to get to 10,000 from FL340, a -1800FPM descent would require 14 minutes, or 100NM (assuming a groundspeed of 450). Based on the assumed descent rate, ATC expects 6 minutes / 45NM (given the above conditions), at the minimum.There is a too fast, because if ATC expects -4000, and you drop like a brick, it could put you in conflict with other aircraft. Basically, if there's an aircraft that will cross well below you as long as you descend at the expected rate, descending faster could put you closer to that aircraft than ATC had intended. There is also a too slow, in that I may need you out of the way of another aircraft, so I need you to descend and clear that flight level sooner rather than later. I also assume the general (Current (Alt/100) - End (Alt/100))*4 rule for pilot discretion descents, which gives you even more of a buffer than 1800, actually, but if you descend at 800 (which I've seen before), you're definitely not going to hit the mark.There's no "correct" or "incorrect" way about the descent. You can use whatever way you deem appropriate. ATC and everyone else in the system will be happier with you if you follow how everyone else does it. VNAV may give you some weird results in the sim from time to time, but it's a sim and it's imperfect (the current NG is also several years old now).One last thing:Don't dial in 250 that high up. You should be using Mach up there, and 250 is what you need to hit by 10,000 in the States. ATC expects you to be well above 250 until 10. If you're not, just as with altitude, it will cause us to vector you out of the stream.

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A few thoughts: M.78/280k is pretty good number to plan with. If you're doing a cruise alt change, just change the cruise alt in the FMC and let VNAV do the work.If ATC starts you down early, use the Descend Now/Alt Int function. That gives you 1000fpm until you reach the VNAV Path.For those suggesting a descent at 320kts, what happens if you get into turbulence? You planned for a nice steep descent at 320, but now you're slowed to 280 for the bumps and you're high. You didn't "give yourself an out."If you are high and planned for a .78/280 descent, you can increase the speed a bit until you get back on profile.Down low, use Level Change for descents more than 2000' or if you need to get down ASAP. Less than 2000', or you want to take your time, V/S.And if Scandinavian gives you something you don't like, just say, "Unable." Big%20Grin.gif

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