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Altitude Constraints FMS and SID

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I've got four days experience with the 737NG and I love it. Problem: I don't know if I'm missing something or I've discovered a simulation limit. The manual says altitude constraints A or B can be entered but don't work on the Legs screen. It also appears that constraints provided by the SID don't work. I am flying SWA2537 route LAS-LAX, which uses BROACH2 DP... I'm departing 01R today due to winds. The FMS knows the first fix off the end of the runway PAWEK is a OVERFLY, but ignores the altitude restriction at the 2d fix BESSY, which is AT or BELOW 7000. It's about a 10nm leg to BESSY so the 7000 restriction is real, and I verified the SIDSTAR file is correct. When I set a hard AT altitude constraint at BESSY for 7000, the Climb screen says ERROR AT BESSY and VNAV won't work. When I delete the /7000 on Legs, the ERROR goes away. The workaround I found was to set the MCP to 7000, which works but this means I need to use the MCP to program constraints instead of the FMS.Why does the FMS say the 7000 AT restriction at BESSY is an error? With no restriction, the FMS forecasts about 7100 at BESSY so I'd expect the restriction to be easily observed.My questions are: Am I missing something (I'm pretty new) or is the FMS simulation missing something. If it is the FMS, does the upgrade to the 737-800/900 fix it? I've attached the SID but it is a pdf, not a txt file... don't know how to attach pdf yet.Dan DownsCorpus Christi TX


Dan Downs KCRP

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Using the -700, I just flew the Boach2 SID out of Vegas and everything worked as it should. I engaged VNAV at 3000 feet and set FL190 in the MCP Altitude window. The airplane leveled off at 7000 in VNAV PTH, passed BESSY, and then continued the climb in VNAV SPD to FL190.Not sure what's wrong with your system. This is what I have loaded on my mine-PMDG 737 install order:PMDG 600/700 V1.2Update to V1.3PMDG 800/900Update to service update 1Update optional models updateLatest Airac (NavData)SID/STAR (PMDG)Floyd


John Floyd

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If it is the FMS, does the upgrade to the 737-800/900 fix it? That and so much more. But remember that simply settings spd/altitude (ALWAYS in that order) constraints does not always mean that it's possible to achieve in the real aircraft. A couple of examples, you set FL180 3 miles from your depp airport, this is impossible. You set an AT or BELOW 220/6000B on your next wpt (MIMMS) but you are at 280/14000 and MIMMS is only 5 NM away. This "common sense" rule applies to any manually entered constraint so make sure it is really possible to achieve. Your example IS possible. Randy Smith


Randy J Smith

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Thanks both for feedback.I've accumulated a few more flights and am feeling more confident; however, I'm still learning the basics of the sim package. I understand the real world constraints. Time to consider the upgrade I guess.


Dan Downs KCRP

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I purchased the 800/900 for the constraints compliance. I didn't notice maintenance board Item 009 VNAV Service Bulletin and discovered the squawk on my own on the same LAS-LAX flight.All worked well departing LAS Rwy01R BOACH2 at BESSY, but as soon as I passed CIVET on the MITTS2 arrival into LAX Rwy27L the VSI decreased to a shallow descent and the VNAV disconnected exactly as predicted by Item 009. The only way I could fly the inbound was without VNAV. Item 009 doesn't give a fix date. I like PMDG to consider taking this discrepancy to task. Seems to me a possible fix is to let the computer target an altitude that complies with the conditionals (in this case AT OR BELOW 17000 AT OR ABOVE 14000 are the conditionals so target 15500) and inhibit disconnect as long as the conditionals are satisfied.Please note I made a purchase to fix a problem that still exists in part. Jeeze.


Dan Downs KCRP

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On the FMC CDU are any cautions or errors displayed such as DRAG REQUIRED, UNABLE TO ACHIEVE . . . , etc.?


Ron Ginsberg
KMSP Minnesota, Land of 10,000 Puddles
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<Negative.. only indication that something is amiss is the decreased rate of descent after crossing CIVET, which has both A and B constraints. The symptom is exactly as predicted on the maintenance board. Sure, after the plane descends at about 200 fpm for awhile the UNABLE TO ACHIEVE is displayed; again, as predicted. I'm gonna try it with a single constraint: Bet is works.


Dan Downs KCRP

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You can also see this poblem if a magenta bug appears on the IVSI during a descent in VNAV PTH. To fix, recycle the VNAV button. The Magenta Bug will disappear and the airplane will resume the VNAV PTH if its not too late. VNAV PTH descents do not use magenta bugs. Sure wish they would fix this.Floyd


John Floyd

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<>Yup.. seems to be two problems. One: It doesn't execute the verticle path after passing a fix with double constraints, and Two: It only looks to the next set of contraints. The KLAX MITTS2 arrival throws both problems its way.I edited the star txt to change the constraints at CIVIT (where I first complained about the 800/900 not fixing the problem) such that instead of a AtOrBelow and a AtOrAbove it only had an AtOrAbove. But, I left the next double-constraint fix (ARNES) as original. Interesting, there is a fix inbetween CIVIT and ARNES named BREMR with a single constraint. So here is what the test looks like: CIVIT 14000A BREMR 12000A ARNES 11000B 10000A followed by SUZZI 9000APMDG FMC only detects the above constraint at CIVIT, and crosses CIVIT way too high to meet the constraint at ARNES. That's a gotchya everytime. Anyway, I was watching for it so I intervened before BREMR and got things lowered and slower with pure pilot technique. Then put it back into VNAV and watched the little blue bug appear passing ARNES just as predicted. There's the two problems in a single easy to reproduce approach. At least I hope it is:-) MITTS2 STAR is attached as a pdf.How do we go about asking PMDG to fix something that is already in the Maintenance Log?


Dan Downs KCRP

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Guest tmetzinger

><the IVSI during a descent in VNAV PTH.>>>>Yup.. seems to be two problems. One: It doesn't execute the>verticle path after passing a fix with double constraints, and>Two: It only looks to the next set of contraints. The KLAX>MITTS2 arrival throws both problems its way.>>I edited the star txt to change the constraints at CIVIT>(where I first complained about the 800/900 not fixing the>problem) such that instead of a AtOrBelow and a AtOrAbove it>only had an AtOrAbove. But, I left the next double-constraint>fix (ARNES) as original. Interesting, there is a fix inbetween>CIVIT and ARNES named BREMR with a single constraint. So here>is what the test looks like:>> CIVIT 14000A> BREMR 12000A> ARNES 11000B 10000A followed by > SUZZI 9000A>>PMDG FMC only detects the above constraint at CIVIT, and>crosses CIVIT way too high to meet the constraint at ARNES.>That's a gotchya everytime. Anyway, I was watching for it so I>intervened before BREMR and got things lowered and slower with>pure pilot technique. Then put it back into VNAV and watched>the little blue bug appear passing ARNES just as predicted.>There's the two problems in a single easy to reproduce>approach. At least I hope it is:-) MITTS2 STAR is attached as>a pdf.A couple of workarounds: Get rid of the conditional waypoints, i.e CIVIT 14000, BREMR 12000, ARNES 10500, SUZZI 9000. You'll still comply with the STAR, but you may need to cycle VNAV after each waypoint (because of the double constraints).Set only the constraint at SUZZI, and then use the MCP altitude to make sure you don't get too low earlier. VNAV ALT will help with this.Third option. Fly it in VS mode and use the MCP ALT and the DES page to guide you.Does anyone know if the 747 behaves better on this arrival?

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Thanks, Tim:Option Three (modified): I'll do what I'd actually do in the real world, which is to fly VS mode with the chart to guide me. In fact, in the real world all I have is "VS mode" or otherwise known on the Century IV autopilot as Attitude mode (it's limited, attitude or altitude hold).But, the maintenance guy has gotta fix the squawk!!What about the NO STATUS on Item 009 VNAV Svc Bulletin?? Does PMDG read this forum??


Dan Downs KCRP

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