So getting a lower speed before the steep descent seems to help.

 

That's exactly what I wrote (even twice) a few posts back

 

 

Changing the CI in flight to control speed isn't something pilots would really do

 

Exactly. Cost Index is not the way to handle speeds. The FMC calculates the econ speeds on the basis of Cost Index. But it is an exact, hard value that is calculated by flight dispatchers (actually computers at dispatchers' work stations), which is used for a particular flight and cannot be changed on the wish of a pilot.

 

using the speedbrake (almost all the time, which doesn't seem too realistic).

 

I remember a flight to Warsaw I was on, speedbrakes were deployed very early after beginning the descent procedure, throughout the descent, approach, beginning of flap extension until short minutes before touchdown. Happens really often.

I talked to a pilot, who used to be my glider instructor, and who is now flying on EMB 175/190 and she told me that the plane is really difficult to slow down so if they get ATC clearance to descent late they have to fly with spoilers deployed during the whole approach.

 

The FMC had speeds like 280 and 260 planned above 10.000 and I changed them to 240

 

If you experience strong headwinds, which means higher costs index (generally speaking as it depends also on other factors) an economical speed at descend is like 315 kt. With lower CI it would be like 296 or 280 like you mentioned.

There is no need to set the speed on descend to 240. It's just waste of time and it's not economical. All you need to do is to set the desired speed at a waypoint you want to decelerate before in the FMC and the FMC will 'create' a point before this waypoint where the aircraft will level off and decelerate. If you plan to have a steep approach after a particular waypoint, there is no need to decelerate more than like 5nm-10nm before this waypoint.

If, considering no headwind and de-ice off, you plan to slow down from say 280kt to 210kt, 10nm is perfectly enough.

But it is an exact, hard value that is calculated by flight dispatchers (actually computers at dispatchers' work stations), which is used for a particular flight and cannot be changed on the wish of a pilot.

:LMAO: Short training leg with lots of work or last leg of a 4-day? It goes up and down at the will of the pilot, just like the jet itself. :biggrin:

Kyle - you mentioned cost index being a cause for this - I don't believe that's accurate. I will have to check with Vangelis to verify with him, but in our aircraft CI isn't just a speed control like it is in some other addons - it works realistically and everything changes, including the calculation of the VNAV path angles and stuff - it should still create a valid path regardless of what the CI is. Changing the CI in flight to control speed isn't something pilots would really do either - you'd just speed intervene on the MCP or go to LVL CHG most likely.

 

I was only going off the forum banter right after the release where people were having issues with their descents. Seemed a lot of them were using 100+ CIs and the suggestion of a more realistic CI resulted in a more achievable descent. Certainly did for me, but that could've been related to a number of other things.

 

Wasn't suggesting pilots change the CI in flight, though. As mentioned by 738pilot, it's something handed down from the dispatcher to be used on the flight. When I mentioned changing the speed in the FMC, it was directly through the VNAV page changing the speed there.

I see you are using the NGX 737, which is a very slippery aircraft. The PMDG 737 NGS Tutorial 1 flight has cases like this where the FMC says that it is not possible (due mostly to altitude and spped limitations), and the tutorial shows you how to use the speed brake to slow down at the right time. So getting that red warning does not necessarily indicate bad flight planning, and although I am no expert on real flying, is probably normal. I consider it just a warning from the FMC that the aircraft will not slow down enough by itself.

 

Henri

Does the 737-700 slow down and descend easier? I mean, do you REALLY notice a obvious difference compared to the 737-800? (Talking about the PMDG versions of course, not the real ones...)

:LMAO: Short training leg with lots of work or last leg of a 4-day? It goes up and down at the will of the pilot, just like the jet itself. :biggrin:

 

The fact that you are able to control it in any way you want doesn't mean you are allowed to control in any way you want

Does the 737-700 slow down and descend easier? I mean, do you REALLY notice a obvious difference compared to the 737-800? (Talking about the PMDG versions of course, not the real ones...)

 

Not sure about the 700 because I haven't bought the expansion but I know the -900 slows easier, and I have heard the 800 is the slipperiest of the NG's.

The there's the budget airline approach, 249.9 knots all the way to "runway in sight" and then throw the anchors out. Well, there's that 3 minute turn-around and the fact there isn't much fuel left. Allegedly.

Well, this is odd. And interesting. While most here say I should slow down sooner I was told on another forum I should speed up to descent faster! I was told that the restriction to stay under 250/240 is mainly meant for when you are not using ATC but it's not uncommon to descent at 260or even 280. So instead of staying in VNAV I did a descent from that 10.000 STAR and using LVL CHG and I noticed that when I turned the speed up to 280 I went down a lot faster: I easily made it to the next alt (5000) in time. What surprised me even more was that on the next leg, where I had to go from 5000 to 3000 pretty quick, I descended even quicker by using the speedbrake! The odd thing was it didn't slow me down but it made me descent faster and I was at 3000 LONG before I reached that next waypoint, which gave me the time to slowdown for approach.

 

So what seems to work best is to NOT slow down but SPEED UP...!? And don't stick with VNAV at all cost but use LVL CHG. I am going to try that flight now that has a restiction of 24.000 feet and see how it goes!

280 below 10,000! Sounds wrong, the logic is wrong why not do 310 and point the nose at the ground, you will be down in no time.

 

Joking aside mate it does not sound right.

Think of it like this... You're already at idle, so the only thing controlling your descent is pitch. Nose over makes you go down faster, and makes your airspeed increase. If you're hanging the brakes out at idle, you'll go down faster for a given speed because the AP is able to lower the nose without risk of breaking the speed restriction you've set. You could also haul the nose up and slow right down if you like. You'll have more time between way points, allowing you to get away with the lower descent rates. There are several ways to achieve the same thing. Not all of them are always practical.

280 below 10,000! Sounds wrong, the logic is wrong why not do 310 and point the nose at the ground, you will be down in no time.

 

Joking aside mate it does not sound right.

 

The guy who told me this was a real world pilot. And the idea behind it (as Mike also explained just now) was confirmed by another rw pilot. So apparently it's not as wrong as it sounds. And... this technique helped me to perform that descend from 24.000 that seemed completely impossible yesterday! I made it to the runway without any problems! I did lower gear a bit sooner then I usually do in order to slow down more for the final approach. But after all the troubles I had the last few days, I never expected being able to get this done so easily!

 

So: LVL CHG instead of VNAV, higher speed when needed and speed brake added when needed. Works like a charm. There isn't a STAR I can't handle now! ^_^

 

I only like to know what the maximum normal fpm is during a steep descend? I can descend with a speed of >4000 but that seems to much. What's more a more regular maximum? 3500? 3000? And what speed in knots is the usual max? The speed tape showed I could go up to something like 330 or even more maybe, but that also seems a bit much... During my 'test' just now I tried to not go faster then 310 and 3500. Of course the test was rather extreme: during another test I did (coming from only 10.000) I could do it with lower speeds.

Couple of us mentioned about speeding up on the last page (including myself), yes it works but I still stick with the 250/10000 restriction personally without issue. I mostly do it above 10000 if my descent has been held up by ATC and it gets me back on path very effectively.

So: LVL CHG instead of VNAV, higher speed when needed and speed brake added when needed. Works like a charm. There isn't a STAR I can't handle now! ^_^

LVL CHG isn't any better, it's just a different button. You could tell VNAV to do the exact same thing via SPD INT or simply changing the descent speed in the FMC. 300 knot at idle is the same whether you're in LVL CHG or VNAV.

The fact that you are able to control it in any way you want doesn't mean you are allowed to control in any way you want

That's true, but it's not sacrosanct like some here believe, giving it mystical powers. If we're running behind schedule and the CI was 15, it's going up.

Well, this is odd. And interesting. While most here say I should slow down sooner I was told on another forum I should speed up to descent faster! I was told that the restriction to stay under 250/240 is mainly meant for when you are not using ATC but it's not uncommon to descent at 260or even 280. So instead of staying in VNAV I did a descent from that 10.000 STAR and using LVL CHG and I noticed that when I turned the speed up to 280 I went down a lot faster: I easily made it to the next alt (5000) in time. What surprised me even more was that on the next leg, where I had to go from 5000 to 3000 pretty quick, I descended even quicker by using the speedbrake! The odd thing was it didn't slow me down but it made me descent faster and I was at 3000 LONG before I reached that next waypoint, which gave me the time to slowdown for approach.

 

So what seems to work best is to NOT slow down but SPEED UP...!? And don't stick with VNAV at all cost but use LVL CHG. I am going to try that flight now that has a restiction of 24.000 feet and see how it goes!

 

Of course if you allow FMC to fly with higher speed the plane will descent faster but the problem starts when there are speed restrictions. And I'm not saying the 250kt below 10,000ft restriction as it is dropped by ATC many many times. But there are other points like SLPs, like IAFs, FAFs and other waypoints at which, according to STARs or IACs, there are different MAX speeds. E.g. approach procedures to LEMD, they have multiple speed restrictions on the way to the airport. E.g. if you approach to one of 18's via SIE, the restriction is SIE at 12,000ft max speed 220kt. Another approach states ORBIS at max speed 250kt and FL190 !

In such situations slowing down to a speed below max authorised speed at a given point is the only option to be able to complete the procedure.

 

That's true, but it's not sacrosanct like some here believe, giving it mystical powers. If we're running behind schedule and the CI was 15, it's going up.

 

Ok, agreed