Pmdg 737ng Descent procedures

[onurksn 1]

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.

[Guest stevepow]

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

[onurksn 1]

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. :(

[Guest stevepow]

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

[onurksn 1]

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.

[michal 44]

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.

[CptSpeaking 0]

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

[pan pan pan 55]

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!

[scandinavian13 5,192]

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.

[Spin737 102]

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."

[scandinavian13 5,192]

And if Scandinavian gives you something you don't like, just say, "Unable."

Correct. PIC Authority is final, but must not jeopardize other flights in the area.Just be prepared for the next instruction of "Fly heading ###, vector for spacing."

[Spin737 102]

"You're number last for the approach."

[scandinavian13 5,192]

"You're number last for the approach."

I've debated saying that a few times, but the closest I'll get to that is "Fly heading ### for re-sequencing."Which really means:"I'm vectoring you off of the arrival because you want to march to your own drum. That's fine. I'll just fit you back in when I fit you back in."

[Berbe 0]

CDA = Constant Descent Approach.

CDA means Continuous Descent Approach.About the descent rate. I read some of you saying it would be 1000 ft/min, 2000 ft/min, etc.You're all right, partially.The main thing to consider for your descent is the angle. Pilots use x° descent anlge, and follow it.Why don't they use a descent rate rather than a descent path? Because your decent rate is linked to your speed (not the IAS - Indicated Air Speed, but the GS - Ground Speed), which changes when you climb/descend or with winds, even if your IAS is the same.The main reason for all that is letting the passengers remain comfortable during the whole flightA quick example: a plane climbing/descending at a rate of 2000 ft/min. If it is in cruise flight (~ M.78), there is no problem at all. Imagine the same descent rate when the plane is in initial approach on an airport. Strangely all passengers will fill a little dizzy... in the best case.Because the descent rate isn't constant, it would be a nightmare (even impossible) to calculate any TOD - Top Of Descent. With the descent angle, it's only some basic trigonometry (need to climb xxxxx ft down with a y° angle, which means I need zzz nm).Your TOD has been manually calculated, now the problem is: how to follow the descent path?Simple: Descent rate (ft/min) = Descent slope (%) * Ground Speed (kt) = Descent angle (°) / 60 * Ground Speed (kt).Uh wait... Descent slope (%) = Descent angle (°) / 60??Let's draw a rectangular ABC, our angle is Â.tan  = BC (altitude difference, ft) / AC (distance, ft) is our slope (%), but  is small, so  is close to tan Â. Thus  (rad) = BC (ft) / AC (ft) = Slope (%)But our angle  is in radians, not in degrees. Pi radians = 180°, so  (°) =  (rad) * 180 / Pi. Let's approximate Pi with 3:  (°) =  (rad) * 180 / 3 =  (rad) * 60.Then, since we said  (rad) = tan  (rad) = BC (ft) / AC (ft) = Slope (%), we have both calculations:-  (°) = Slope (%) * 60- Slope (%) =  (°) / 60Note: BC & AC must be comparable value, i.e. with the same unit. Typically, you'll get AC distance in nm and BC height in ft, and since a feet is smaller than a nautical mile, it's better to convert nm in ft.You've got your TOD and your descent path. The last step, in the cockpit, is to monitor your speed and vary your descent rate accordingly. Prepare some Excel calculation... Or let VNAV do the job, which is maybe more realistic but lots less fun!Remember to add some safety distance. If you are to respect the 250 kt under FL100 restriction, remember that you'll need to anticipate by reducing speed or by stopping/reducing your descent dramatically just before reaching FL100, which means some distance flown above the descent path... Maybe start descending sooner to make sure being on/under the descent path.

[Spin737 102]

All that work and you've just described what VNAV will do for you. VNAV can do a little hunting, especially without descent winds, but without a STAR, VNAV basically gives you a CDA.