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Guest Foizman

PMDG 744 Descending

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Hi Folks,thousends of postings have been placed in this forum concerning VNAV-descenting on T/D. But what is the sucus? Didn't find a summary. Is anybody out there which has a super-exakt QUICK-Tutorial for just this stage of flight? My goal is to fly as realistic as possible.So to those few who know the anwser please give me a short procedure-description for the following scenario:- flying on FL 390 with cruise speed (e.g. mach .82)- T/D 50nm away- FMC fully programmed, it ends right bevor the STAR, which at this point was not transmitted by ATC so far.- TL may be known through ATIS and entered in FMC (FORECAST)- Landingconfig entered on APPROACH REF-site, hence VREF is known.So what do next? Contact ATC for requesting to leave FL390, he maybe says something like "descent to FL200". During Descent (and before reaching FL200) he might advice you to descent to FL85 etc. I've read that there are lot of problems when staying in VNAV-PATH mode (>-5000ft/min descentrate, thrust stays e.g. 70% and not ad IDLE as expected, descentpath is leveling off). Thats not reallife-behavior I think. In addition I've heard that reallife-pilots use the flaps at 1

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ATC will generally give you descent in time but if you reach your T/D with no instruction from ATC then you should contact the controller and ask for descent..something like "PMDG747 requesting lower"what i would do then is dial in the altitude the controller gives me and hit FLCH, this gives me control over my speed and altitude. Depending on ATC instructions you should have no problems. If you are given a waypoint to cross at a certain altitude and speed then use the green arc in the ND and monitor your descent rates, i find reducing speed first and then descending is the best option for me, again FLCH works out for me. Under 10000ft i generally switch to Vertical Speed mode, reducing speed under ATC instruction and getting my flaps down and configured for landing. thats what i do, regarding specific real world procedures im sure others can give more detail

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What i do to descend is type my required altitude into the CRZ/ALT in the fmc see "jpeg" then execute it ,usually descends around 1200 ft per.As far as flaps and at what speed it is indicated on the PFD.Hope it helps .Phill

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If you are within 50 miles of TOD and the controller tells you to descend, Vnav

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Hi Sam,will try your descriptions soon and report. Thanx a lot anyway for being that exact!So to sum up it's not necessary/usual to lower the flaps to e.g. 1

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Flaps for descent:Generally I'm finding that VNAV PATH's target descent speed is around 300kts. That's too fast for even the first notch of flaps (280K Vmax/1st notch). So we're still left to slow down, someway, to even get that first bit out. We can speed intervene into the VNAV PATH descent to slow down, but there

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Hi Sam,ad "flaps", found it: (see AOM 9-11 Leaving Cruise par. 3) "The use of flaps...is not recommended ... as this places significant wear and tear on the flaps..."Before I'l try your hints I'd like to check if we talk about the same, see image below:http://forums.avsim.net/user_files/146055.jpgUsing some flaps below 280kn is allowed e.g. flying a holding (6001 - 14,000ft, 230kn) or short of 240/10000. But why do we use it if it's just good for burning more fuel and making them get broken?And: How do I continue the descent below 10.000ft if ATC doesn't give me some speeds? Looking on some VATSIM-STAR charts, there are lots of height-restrictions but I can't find any speed restrictions. Usind "Flap Maneuvering Speed+10kn" (See AOM 9-12 Approach Speeds par. 4) sounds great but nobody tells me WHEN to lower the flaps to e.g. 5

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That's a great diagram. I tried a flight where I speed intervened to get below Vmax-flap speeds then drop 'em ASAP. The PFD's yellow caution band was all over me. I was above and below path throughout the descent. I had a couple of 30 degree banks as my STAR progressed. One time, I had the lower band come up and contact the upper yellow band. There was no where to go. I was in trouble. The diagram suggests an idle, path descent. Then until the first notch of flaps at 270kts as the deceleration segment progresses. This is fine, but why am I throwing out all that drag early? I ran my descent again "clean" and found the PFD scheduled flaps 1 at 240kts. I really don't know why I would want to drop in that extra drag early. I'm just burnin' more gas. The PFD's schedule seems to work fine. It seems PMDG did quite a job on the logic for these flap schedules and yellow band caution speed annunciations. When I played with a forced flap descent, those yellow bands were really hoppin'. The bands were not just indicating a Vref based on a 30 degree bank. They were real time as they showed me min-max speeds for level flight, then pinched in as the airplane banked and/or changed altitudes for those STAR's path progression and course changes. It was very impressive. As I said, by speed intervening and early flap extensions, I got myself into trouble a couple of times. That said, my best guess is that the best operational practice is to use the PFD's green flap extension recommendations. Again, I think that airspeed is the target. Flaps need to be extended in support of airspeed targets. Now about airspeed targets. I have been listening into my local approach controller for the last several weeks. He gets the handoff from the enroute controller. He gets his airplanes at between 10000 and 14000 feet, 20 to 30 miles from his runway's IAF. Generally, as the airplanes check in, he just gives them the current altimeter, but sometimes he'll ask them for their airspeed. My impression is that this is more of a cautionary "Woah there, big fella" call. Only once have I heard the controller specifically speak to someone on that initial call about speed. A Southwest 737 came blastin' in high and fast. The controller said "Reduce to 250" then went on, wanting to know just what the heck what was going on. As the airplanes enter his airspace the 250kt speed limit is strictly observed. So when passing through 10000 ft, stay at 250kts until . . . told to do other wise!As the traffic progress along the STAR, the controller will start controlling. He will immediately start controling their descent with altitude instructions. At about 10 miles from the runway's IAF, he will start giving vectors and speed reductions as required for separation. Sometimes it's just amazing to listen to these guys weave the commercial traffic through a sea of GA traffic. Sometimes it's comical and sometimes it's not funny at all. I've held my breath a couple of times. On real stormy days when all the GA guys are home sippin' martinis, I'll hear "Descend direct (IAP)" Then clear to join the localizer, runway 26L ILS approach." That's it. It's so much more peaceful on the stormy days. However almost always, I'll always hear "Reduce to 220" (or less) at some point. His runway has a 10 mile final (from the IAF). When I

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One of the problems I find with the ATC in FS2004 is that they descend you too early and if you try to hold off a little longer you end up with an "expedite your descent to....." request. This tends to scew up the VNAV profile.On a typical flt you would program the FMC according to what you would expect to get, or have been cleared, to do by ATC.In the cruise you should have VNAV PTH showing on the PFD if the aircrafts alt is the same as what is set in the MCP alt selector. When you are cleared by ATC to a lower altitude select this in the MCP ALT window. When the a/c reaches T/D the thrust levers will close (IDLE then HOLD) and the aircraft will decend in VNAV Path at the programmed speed in the descent page. The descent winds may vary according to what has been entered. The elevators will attempt to maintain the path. If the airspeed gets too high you should get a drag required msg. Use speed brake to slow down. If the airspeed gets too low then the A/T will apply enough thrust to bring the speed back to programmed descent speed. If for any reason you have to level out somewhere then this would be set in the MCP alt window. Just before this alt is reached VNAV PATH will cahnge to VNAV ALT and the A/T will change to SPD. You will see the aircraft get high on the VNAV path from here on. When you get a further descent sel the new altitude in the MCP and press the button. Because the aircraft is above the path you will see VNAV SPD. You can do one of two things and it will depend on how high you are.1. Increase the speed. Wind up the airspeed. More drag, steeper descent.2. Use speed brake.Once you are back on the path close the speed window (press the speed knob) and it will change to VNAV PTH. You will see 2 green donuts on the ND which are the deceration points for 250 kts. When the A/C reaches the first one it will commence a spd reduction. Keep an eye on your PFD annunciator to make sure it stays in VNAV PTH. If it goes to spd than that is a cue to you to do something to get back on path. If you are in VNAV SPD before you get to the first donut it will not slow up....you have to do it. If you are frequently off the path because of ATC etc then I suggest you use another mode its easier. FLCH is good because all you have to do is select the cleared alt and press FLCH and it will go there (up or down). FLCH is a good "Oh s##t" mode. All you have to do is select the alt you want to go to and press FLCH and set the speed you want. There are traps with this and V?S but is beyond the scope of this post.When you are ready to put flap out (approx 15 to 20 nm from touch down) and you are still in VNAV and on the path you will need to open the speed window to adjust the speed bug. This will change the mode from VNAV PTH to VNAV SPD and the A/T to SPD. You can then reduce your spd to the min clean spd and start putting out your flap. F5 to F10 is good for manoeuvering close in for the ILS. Sometimes for close in work V/S is good because you can fine tune your rate of descent easily with the sim. Just remember during the descent to make sure that your distance to go is more than 3 times your height/1000. ie. 10,000/1000 =10 x 3 = 30. You will need to add a little distance for slowing down to put out flap etc ( say 5 nm no wind, 250 kts descent and mod weights) but if you are inside this then you will most likely need to do something to get down quicker..speedbrake or slow down and put out flap earlier. The gear in this A/C is a great source of drag...just obbserve the placarded speeds. I have attached a diagram of good Flap positions to be at when flying an ILS.Sorry about the long post. VNAV is a complex mode to describe in a nutshell. Hope this helps anyway.CheersSteve

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Oh come-on. We need some guidance here!

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Nice diagram, Volker, but I'm betting it's not from a 744 Manual.I don't understand why folks are having so many problems with VNAV.Yes, you are right, 70% N1 is not normal for VNAV idle... Having said that, I've never seen it in the PMDG 744. My N1's are mid 40%'s during idle descent, so I suspect that your joystick throttle is interfering with PMDG's idle... or you're using "DESCEND NOW" ...which is not, initially, idle thrust.Once you have corrected your idle problems, most of your descent profile problems will disappear (assuming no unforseen tailwinds).Having said that, if your airspeed is too high and your aircraft is drifting above profile, the FMC will tell you what to do (DRAG REQUIRED). This is when you use the speedbrakes. Flaps should not be used for slowing the aircraft... and using flaps above 10,000' is a waste of fuel and adds to maintenance costs... unless your airport altitude is just below this.Let's not create ficticious procedures, shall we, until we have sorted out your idle problems ;)Cheers.Q>

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You mean this?"I've read that there are lot of problems when staying in VNAV-PATH mode (>-5000ft/min descentrate, thrust stays e.g. 70% and not ad IDLE as expected, descentpath is leveling off)." My take was this was a summary of various, assorted, unrelated problems that had been read about Vnav. However, idle at 70% N1 is a stuck . . something! Took an airplane out for a power run after an engine change the other day. The subject thrust lever wouldn't go a knat above part power (well, we used to call it that, anyway). Goofy mech had a bolt in backwards. Hey, it wasn't me. Honest.

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Hi Q.,no way Sir, not from a 744 manual ;-)painted it from Sam's posts. Besides the flaps it seems to be ok so far.hmmm...don't think that the VNAV-thing is that easy and not worth being discussed en detail. Just have a look at Mike Ray's procedures manual (page 217, VNAV SECRETS).Maybe you misunderstood: in my Sim there is no "N1 70% IDLE mode", have never observed such a behaviour. But prior posting this threat I had looked up the forum and I found things like "PMDG Bug cause 70% IDLE descenting in VNAV-PATH" etc. I just summed it up.greets,Volker

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Hi Steve,thanks for the image, it's in the AOM. Problem was (when I found it) that there are no distances/speeds in the diagramm, just "lower flaps to 1

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"painted it from Sam's posts. Besides the flaps it seems to be ok so far."What?!! Here I was all struttin' around cuz I thought it was from some ops source . . . I'm gonna need thrropy now. But that is what I was proposing. Sure wish I really knew! That picture's very well done and worth a thousand words. I need to learn to draw. Regardless, Vnav's really seems to be the toughest part. Sure was for me. That's what drew me in . . . and made it such fun. I didn't get it.

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hehe,drawing vs. the Power of Words;-)

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Hi Volger,Got your email, I think this one has been answered though by other people,it looks a bit too complicated for me anyway.CheersJon

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