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jdyoung

Please help me slow down!

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Hello all!I am the proud owner of the PMDG 736/7/8/9 and fly it daily. I am having a problem with slowing the aircraft to proper approach speeds. Flight to LAX - The aircraft is on CMD A, VNAV and LNAVFL370 at .80 ATC tells me to descend to FL240. I dial 24000 into the MCP and hit LVL CHG. The nose dips down and I begin my descent. Reaching 24000 the aircraft is still at .80. Shortly thereafter ATC tells me to descend to FL160. Okay, same procedure, but this time after dialing 16000 I change the MCP airspeed to 270 knots and hit LVL CHG. Here's where the problem begins.The aircraft dips only slightly to begin bleeding off the excess speed. This gives me a descent rate around 500 fpm. Before the aircraft has had a chance to reach 270 and 16000, ATC has told be to descend to 5,200. Alright, fine but now I need to get below 250 knots. I enter 250 into the MCP speed and 5200 into the altitude window - hit LVL CHG. Again....the aircraft takes forever to bleed off the speed and descends verrrryyyy graaadduuuuallly as a result. Problem is, I'm now at my FAF at 9,000 and should be at 2,200! ATC tells me to descend to 2,200 and to contact tower. Wait a minute! My vref (plus 5) is 163 and I'm screamin' in at 250 at the outer marker! I can't even get it slowed enough to get within flap speeds. I've tried using intermittent speed brakes during descent but the aircraft still seems to take forever to bleed off speed. At times when I'm frustrated I just unleash the speedbrake and leave it deployed for up to one minute but it has minimal effect. In the meantime I'm "wasting" precious airspace as I grow closer and closer to the runway but I'm not slowing down, nor going down, very fast. I may have 220 entered into the MCP but the aircraft can't seem to slow down past say...255. One last piece. ATC begins my descent about 10-15 miles before I would have reached my FMC TOD. So it's not that ATC is keeping me up there until the last possible second and then expecting me to drop out the sky like a rock and land smack dab on the numbers. What am I doing wrong? Should I just extend speedbrakes when I hit LVL CHG and leave 'em up until the speed is acceptable? Is that common practice? I've read manuals repeatedly and have tried the same flight/approach over and over again. In the end I'm always too high and too fast. Any advice would be greatly appreciated. The passengers are getting pretty upset at the unexpected dive bomb approach coaster ride they get at the end of a relatively uneventful and enjoyable flight.Thanks for reading and thanks for your ideas.John

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Guest brettdonahue

I am not a pro, and I would probably make some pilots mad, but you could always disable the autopilot and auto throttle, and do a manual descent. I don't use the VNAV option, just auto-throttle and that little dial underneath. That way I can slow down or speed when I need to.:-wave

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Guest _sebastian_

Hi John.1. The trick is to reach the flaps-up maneuvering speed at an appropiate time. This means that you have to set the airspeed cursor to the flap maneuvering speed displayed as "UP", not to 250, around FL120. Once flap 1 is called the decelleration happens fast.2. (Non-ATC) Get a weather software, and analyze the descent forecasts (AS2004 is excellent). Enter these into the DESCENT FORECASTS page in the FMC. If you have a strong tailwind you will continually receive a DRAG REQUIRED until VNAV eventually disengages. With correct forecasts entered, VNAV should be able to bring you down all the way./seb

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I also never use the VNAV. I always turn down the speed before the descent. For example, if I'm cruising at .74 I immediately dial in .70 before engaging the VS. I usually descend at about 1800 fpm and as the descent continues I keep turning down the AT set speed. Below FL260 I usually keep speed between 260-270 kts. Also, the ATC in FS is not very accomodating to large jets. I plan my descent well ahead of time and use the published STAR if available. I often ask ATC for a lower cruising altitude well ahead of where it normally starts you down. I try to be down to about 15,000 and at 260 kts when I'm about 70nm out. If you let the FS ATC handle all your vertical navigation you will get into exactly the situation you describe: high and fast. This is especially true if your approach will not include one of those long downwinds that ATC sends you on. About the only time lately I recall having to hit the brakes was a flight from KBDL to Orlando when I was vectored directly into runway 18L while coming in from the north. I also completely disable the AT on approach. I prefer to handle the throttle myself so I don't get any surprises when I disengage the AP for landing. Mike

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John,You have just discovered the chore of not planning your descent in advance. - The NG is a slippery bird and does not allow you to sink and slow down simultaneously. - The FS ATC has a lot to be desired. I would suggest you quit the IFR ATC during descent and approach as it is totally out of line. - Plan your descent using the 3:1 rule (do a search on this). It's a crude but effective method to estimate your TOD. Add or substract some nms deending on wind conditions. Or you could use VNAV which with the right input will do these calculations for you.- Use the speedbrakes whenever you need to. But know when your hopelessly hot and high and act accordingly. Make a 360 or something like that. ;-)Hope it helps,

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Thank you all for your answers. I'm determined to land this bird safely and without breaking the sound barrier. ;-)I will attempt another flight tonight after kids go to bed and try your suggestions. The help is greatly appreciated! :-)

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I just remembered a couple of more items after just doing a flight ;-) speed is a max. of 250 kts at or below 10,000 by regulation. By the time I'm about 30 miles out I'm usually running about 180 kts with 1 or 2 notches of flaps. Planning is the key to whole affair. Good luck. Mike

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Adding to the above...I typically use VNAV down to 10,000 then I use LVL CHG from there. I always use a STAR if it is available. The STAR is a good starting point for good decent planning. If you program the FMC properly using the decent planning page, the FMC will set an accurate TOD.I usually fly using on-line ATC so they typically do a good job of giving me a nice step down below 10,000. I use the level offs to reduce speed. I also follow the flap schedule closely. I typically will fly 250 knts until about 20 miles from the turn to final. 210 knts up about 5 miles from the turn to final and then slow to 180knts. 180 to the marker, drop the gear, drop the flaps on schedule, arm the auto brake and air brake (spoilers) and then bring her in.On occasion I have been asked to keep the speed up and fly 210knts to the marker. The landing gear work well to slooowwww things down. :-)Good luck!

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>Thank you all for your answers. I'm determined to land this>bird safely and without breaking the sound barrier. ;-)>>I will attempt another flight tonight after kids go to bed and>try your suggestions. The help is greatly appreciated! :-)> I suggest that you try the various VNAV DEScent modes. The NG has become very good at descents (although not as good as the Classic) and many if not all pilots (except SouthWest) use the autos more often on decents than not. Don't believe that the A/P will descend and slow at the same time, this is impossible (There is no spoon, sorry wrong movie!). At best, the FMS choses a profile with the data you supplied it.Remember1] VNAV PATH means it keeps the path and not the SPEED. You the PIC must monitor and adjust as necessary.2] VNAV SPD will keep, well the SPEED! It will not keep the path whatsoever. It will keep any restrictions on the way down though but these are dynamically kept, say @ XYX 250/12000 it will keep this restriction BUT might in fact reach 12000 prior to the FIX and will temporally level off UNTIL passing the fix and continue it's descent. You can of course throw out the boards to adjust your descent or add throttle, in this way you CAN keep the path at least closer than leaving it on it's own.[h4]Randy J. Smith[/h4]

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Guest nattydread

I have certainly learned that you cant descend and slow at the same time :) You have to throttle down, then pitch down. I'd suggest switching from LVL CHG to the vertical speed mode and setting it to atleast -2000ft/min...as high as -3500ft/min may be just fine, especially at higher speeds before you break 10,000ft. In auto-pilot you have to assume you may over speed, expect to bring the throttles back(to idle isnt a bad idea) and use the speed-brakes.Once you start getting radar vectors just hand fly her...she handles great. Your powerband between landing and about 7,000ft(whatever altitude given before they bring you down to glide-slope intersect altitude) is 55%-70% N1. After passing the IAF you can start thinking about reducing speed to 210-180kts...60-70% N1. Drop N1 to 50-55% or even as low as 40% whenever you want to slow down by 20 or more Kts. Once you are at 10 deg flaps you can keep the N1 at 60%(give or take 5%) and you should be around 180-190kts. Just before or just as you intercept the GS drop N1 to 50-55% to help her slow down(or actually not gain speed) before you begin descending and as you deploy your last set off flaps, then bring her back to 60% to have her settle in at your approach speed. Look for 700ft/min descent and adjust your power +/- 2-5% to adjust your speed.

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Guest cfm56

I just have to add my two cents on this: you guys have some neat tricks to handling this bird on this phase of flight. However, have any of u ever wondered how a real NG pilot deals with this 737 "character flaw". I was on a 737-800 flight once and I remember noticing this ridiculously looking high angle of attack just minutes bfore the pilots dumped full flaps, landing gear and turning final. On the continuation flight to jfk i noticed them doing the same thing on aproach just miles from the CRI vor bfore bginning the canarsie visual approach to rny 13L at JFK.( only this time they put in about flaps 15 or sumthing like that) I said this to say this: Ive found an easier way to get the bird down to altitude at the right speed. The thing we are missing here is the fact that each aprroach has its own altitude and speed restriction. Each telling the pilot that in the absence of atc instructions u need to be at this altitude and at this speed. These speed/alt restrictions ultimately lead u to the final approach fix which gives the minimum altitude u need to be at when the glideslope intersects that altitude and the final descent to the airport is to begin. Ive read from a real 737 pilot somewhere that u cant rely totally on the speeds and altitude given by the FMC. To get the bird to do wat u want it to do, u have to imput "your own" speed/altitude info into the fmc. And in this case use the speed and altitudes that u may find from approach charts. Ive found the VPN kneeboard from avsim(with a few personal mods of course) very useful in helping me determine through real world metars and TAFs wat runway is in use. And 8 times out of ten my guesses are correct. I know how hard it is to get approach charts but fscharts.com has some old but useful charts that can give u an idea of wat altitude u need to be at to intercept the glideslope. And (I dont know for sure, but im guessing) that at the final approach fix u want your speed to be somewhere in the range of 1.3 the stalling speed of the aircraft. Therefore I just input this altitude and speed restriction into the FMC (minutes even hours from top of descent) and the fmc then recalculates all the in between altitudes, the 250/10000 transition point, and even the T/D point for me. Or, in other words, it shifts the TOD, 250/10000 transition point back a few N.Miles in order to reach that resriction. And trust me it works - since ive been following this method, there was only about 3 situations where VNAV disconnected and that was only due to high and shifting winds during the descent. Trust me guys it works. Piggy backing on wat some other dudes said, planning for each phase of flight IS the key to this. Yes the 3 to 1 rule works, and they do sometimes use it in the real world according to one ERJ pilot, but y use it when u have an fmc that can do it for u. I havent began to study up on the different procedures they use for this phase of flight as far as being at what speed and where(after the 250/10000 point ofcourse) but I will try to ask one of the real pilots that I c on the bus. I encourage everyone to study up on this stuff, cause knowledge is the driving force bhind all of this.Gideon.

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Guest teeloo

My two cents:VNAV descends do work without ATC restrictions. It even gives you the point of level off for descel (expl. 10.000/250) and the point of re-initiating descend. Works for me including the altitude restriction at the approach fixes.Mind you that the FMC's altitudes at the FAF and other points are not related to the mandatory alt on the appr. plate.Of course delaying at the T/D (because the MCP alt is still set at Cruise Level for example) or whatever, makes all target altitudes impossible. The FMC's calculated VNAV descend profile is based on the most optimum path. So delaying any of it (tailwind is a big factor too if not given to the FMC!) you'll never get back on the path. (spd-brakes is the only option then).What I do with VNAV descends:Set MCP well on time to a lower FL/Alt (prefer. FAF alt). Check the winds on descend: tailwind is a killer for the profile.Check the Desc. Page on the FMC for all it's values.Teeloo

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"Yes the 3 to 1 rule works, and they do sometimes use it in the real world according to one ERJ pilot, but y use it when u have an fmc that can do it for u." One answer to this rhetorical question is: what happens when your FMC blows a fuse? One of the fun things for me in simming is making sure I can handle the plane manually. It's a carry over from my real flying days when I had drilled into me to plan for the worse at all times. I do like the AP for the 737 and if I have a very tricky approach (low vis and x-winds) I do rely on it for most of the approach, but in more benign circumstances the disengage lever is pulled fairly quickly and I hand fly it in. Mike

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Guest Hawkeyeted

>"Yes the 3 to 1 rule works, and they do sometimes use it in>the real world according to one ERJ pilot, but y use it when u>have an fmc that can do it for u."I've written in another thread about VNAV descents, but here is the short version:VNAV does one of two things; either a PATH descent (analogous to the Glideslop of an ILS beam), or a SPEED descent. It does NOT do both at the same time. If you want to control BOTH speed and descent path, you need to disengage the VNAV, and manually use the V/S and SPEED on the MCP.That said, VNAV descents are hard to use with FS ATC, because it almost ALWAYS starts your descent at 100 nm from the airport, give or take a miles based on cruise alitutde. This is NOT the most economical descent profile, which is what the FMC is trying to achieve. (Conversely, VNAV PATH descents are AWSOME when flying on-line. In reality, ATC will clear a descend at pilots discretion which allow an FMC to fly the most economical descent profile.)Your best bet is this; when ATC clears you for descent from your cruise altitude, VNAV descend utilizing FLCH until in the FL 120 to FL150 range (basically use FLCH until the ATC descent clearance below 10,000 ft.) When ATC clears you for the descent that will bring you below 10,000 ft, turn off VNAV, and use V/S and SPD on the MCP. VNAV with FLCH will get you down from cruise level quick enough that you can then manually decelerate to 250 kts prior to descending below 10,000.Additionally, try experimenting with the FMC "DES NOW" function! If ATC clears you to say FL210, set FL210 in the MCP, press "DES NOW" softkey in the FMC (on the decent page, I think it's 6R). It will descend at approximately 1000 f/m, until intercepting the original calculated decent PATH. Hope this helps!/R,Ted

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Guest cfm56

Check this out Ted,Firstly I want to say that I wasnt attacking anything u said If I came off that way plz accept my apology. But check out what the FARs have to say abut the pilot in command: Im paraphrasing, He is the final authority as to the operation of that aircraft. FAR 91.3. Therefore one of your jobs as PIC is to make sure that the instructions u are getting from atc are in accordance with the performance of your aircraft. So if they are telling u to descend 100 n.m. when u need 130 u got to let them know. Or in our case, ask for a lower altitude. I normally ask for a ridiculousley low altitude like 2000 from a crz alt of 370.

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I DID IT! :-hahA fair amount of descent planning made a big difference. Switching my mode of descent from LVL CHG to SPEED (and use of V/S) made the rest. It was low and slow for the approach! Hit the Vref spot on and floated gracefully down to a feather soft touchdown at LAX! YAHOO!I can't wait to try it again! It's a truly satisfying feeling to have a near perfect flight. My wife now thinks I'm up to something because I can't stop smiling! ;-)Thank you all for your help. Your experience and knowledge are appreciated. It's back to the skies for more practice!Happy flying to all! John

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I normally ask for a ridiculousley low altitude like 2000 from a crz alt of 370. With steep fuel prices I would gather that staying as high as possible as long as "feesable" would save a company $$$ as this too relates to pilot discretion.[h4]Randy J. Smith[/h4]

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Guest cfm56

Hey Randy, nice to hear from u again."I normally ask for a ridiculousley low altitude like 2000 from a crz alt of 370." When I made this statement, I was refering to the Top of Descent that the FMC gives me after Ive made all the speed/alt adjustments in the approach legs of my flightplan. What I ment to say was that at this T.O.D I ask ATC for this "ridiculousley low altitude" because they sometimes give level offs and descend TO s that are not in accordance with the PMDG 737 performance. Everyone here knows just how unrealistic FS Atc is. So this is just my trick around that to avoid comein in too high and too fast. So as far as economics goes I dont think it applies to this case since i normally do the VNAV on, power off, fuel flow at 1.3sumthing per engine Almost always to that "ridiculousley low altitude". where i would get Approach clearance, slow down, contact tower, dump flaps/gear and land. Thanx for pointing that out though.Gideon.

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Ah I understand Gideon. You looking forward to the 744?[h4]Randy J. Smith[/h4]

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Guest Hawkeyeted

>Check this out Ted,>Firstly I want to say that I wasnt attacking anything u said>If I came off that way plz accept my apology. But check out>what the FARs have to say abut the pilot in command: Im>paraphrasing, He is the final authority as to the operation of>that aircraft. FAR 91.3. Therefore one of your jobs as PIC is>to make sure that the instructions u are getting from atc are>in accordance with the performance of your aircraft. So if>they are telling u to descend 100 n.m. when u need 130 u got>to let them know. Or in our case, ask for a lower altitude. I>normally ask for a ridiculousley low altitude like 2000 from a>crz alt of 370. >> ?????I'm really confused by this one? I never said anything about accusations, nor violating FAR's.

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