Hi All, Just a quick question: I was doing some approaches into EGLL using the LAM3A arrival. I noticed that the version of the STAR that I had did not have the crossing restriction of FL250 overhead LOGAN (which is indicated by the charts I have), so I put it in manually. Upon reaching the TOD, the autopilot initiated a decend such that LOGAN was crossed at FL250 (give or take a few hundred feet). The next crossing restriction is to cross SABER at FL150. However, the autopilot stopped following the computed decend path and only decended at a few hundred feet per minute after LOGAN causing me to overshoot the restriction at SABER. I then recycled the VNAV and the airplane raced to meet the restriction. This basically went on for each of the following waypoints: I had to cycle VNAV to get the autopilot to follow the computed path. In each case, I could see my deviation between actual path and computed path just increading. This leads me to believe that if you make modifications to a STAR, there will be some problems having the VNAV path followed. Is that so? I had no excessive winds, nor any odd indications on the FMA.Thanks, :-waveBoazEKCH

>Hi All,>> Just a quick question: I was doing some approaches into EGLL>using the LAM3A arrival. I noticed that the version of the>STAR that I had did not have the crossing restriction of FL250>overhead LOGAN (which is indicated by the charts I have), so I>put it in manually. Upon reaching the TOD, the autopilot>initiated a decend such that LOGAN was crossed at FL250 (give>or take a few hundred feet). The next crossing restriction is>to cross SABER at FL150. However, the autopilot stopped>following the computed decend path and only decended at a few>hundred feet per minute after LOGAN causing me to overshoot>the restriction at SABER. I then recycled the VNAV and the>airplane raced to meet the restriction. This basically went on>for each of the following waypoints: I had to cycle VNAV to>get the autopilot to follow the computed path. In each case, I>could see my deviation between actual path and computed path>just increading.> This leads me to believe that if you make modifications to a>STAR, there will be some problems having the VNAV path>followed. Is that so? I had no excessive winds, nor any odd>indications on the FMA.>>Thanks, :-wave>>BoazSome Standard Terminal ARrivals have the altitude restrictions, others don't. You'll just need to manually enter the altitude if it doesn't have the restriction(s). Hope this helps:-)

Hi,I've been running into exactly the same thing, though it occurs for me even in the absence of a STARS. I bought 737NG + the 800/900 upgrade a week or so ago and have had this problem with vnav throughout the 2 tutorials written by Clausen and Metzinger's series (all of them excellent work and very much appreciated by the way!).In all cases I'm flying with no weather at all. In one tutorial you use the DES NOW option to start a descent early. It is supposed to descend at 1000fpm until the original vnav profile is intercepted. I watched the path deviation on the des page. It approached and flew right through the intersection without changing anything. Cycling vnav caused it to race to catch up until it finally disconnected with an unable next alt message. Though the intersection vnav stayed connected and the mode annunciations in seemed correct. If I remember they were FMC SPD, LNAV, VNAV PTHSimilarly, I often watch it fly right past alt and spd/alt constraints after achieving the first of a series(though it seems that speed often is achieved). Again, cycling vnav seems to work. It can be very bad on final to a non-precision approach as it is harder to cycle vnav in time. These constraints are those in the tutorials which I assume numerous people have run through without problem.In all of these flights I'm flying the 700. (I do also have the temp update for the 800/900). I can fly the secent and approaches with fl chg and vs but I'd really like to use vnav as well.Anyone have any idea what's going on? Thanks!Mike Potter (767PIC, 737NG)

Hmm, I assumed that this would happen even if not using a STAR. I almost always use a STAR as the basis of the flight and follow that until otherwise directed by ATC, so I can really confirm that part of the problem. It would be nice if some of the clever heads (PMDG or some of the excellent testers) would pitch in on this one.Thanks :-waveBoazEKCH

I have left out the FL250 descent planning by LOGAN out of the LAM3A star for egll as this altitude could equally be FL220 from the charts.FL250 by LOGAN for aircraft flight planned at FL300 and aboveFL220 by LOGAN for aircraft flight planned at FL290 or below.I have experienced problems with the soft constraint at or below and vnav not meeting the restrictions. In a recent flight from egss to egph, top of descent was shown after the restriction by MARGO at or below 26000, when I was higher.Simonhttp://homepage.ntlworld.com/simon.butler2...usefulfiles.htm

Hi all,maybe that problem have something to do with the new FSUIPC 3.30? :-hmmm Regards,Jorge Niny

Hi Jorge, It is a viable suggestion, however I am not using that version of FSUIPC...Thanks,BoazEKCH

I'm also having troubles when trying to initiate cruise descends last days. I have to put it descending 50 miles before T/D, then it goes with -1000 and should start going faster when passing the point. But it does not. It just keeps going with 1000 and thats all. No idea why.

GeorgIt should not descend faster when passing the T/D on a DES NOW. Remember that you are way below the predicted path when you pass the T/D. You will only steepen the descent when you catch up with the predicted path. Not before that.http://forums.avsim.net/user_files/83703.jpgHope it helps,

Yeah, I know that. I wrote a bit wrongly. I mean that it never goes more than -1000 if I start descend before T/D. Even if I select lower altitudes for some points etc. It misses the correct ones.

My first post...I too have this problem (the one that started this topic), however I find that pressing ALT INTV sorts it out - I can't see why it should, but it does.David Jordan.

Just tried the LAM3A arrival into EGLL RWY 09. I used the EGLL.txt file shipped from Navdata. That STAR has four hard altitude contraints:SAB at FL150LAM at 7000LAM275D at 4000IA7.5 at 2500Setting the MCP to each of the contraints every time. The arrival went without a glitch. Though the descent between LAM and LAM275D seems to be way to shallow.Now guys. If you are flying this STAR using VNAV PTH DES setting the MCP to the hard altitudes you have to watch out. When the aircraft is reaching the MCP altitude it will revert to a.) ALT HLD and FMC SPD or b.) VNAV ALT and FMC SPD. Wether it reverts to a.) or b.) depends on your settings in the styles menu. If you have VNAV LAT checked b.) will happen, otherwise a.)Now. This revertion happens a bit before MCP altitude. If you change the MCP to the next hard altitude before the revertion VNAV PTH will be kept. But if you change the MCP altitude after this revertion you have to a.) engage VNAV again or b.) press ALT INTV to engage VNAV PTH again.If you do not set the MCP to the hard altitudes (It is good practice to do this though as it increases your awareness of what VNAV is doing) but rather to the 2500 feet at IAP the VNAV function will step down nice and smoothly without you needing to reset anything. So again. Check your FMA and see what it tells you. This is where the NG's automation tells you what it is doing. The buttons and knobs on the MCP is where you tell the automation what to do.Hope this straightens out some of the question marks in this thread.If any are still bent I'll be more than happy to clarify! :-)Hope it helps,

Hmm, I always press ALT INTV, but it doesnt seem to be helping me. I have VNAV ALT Turned on.

Hi Mats, Good points you raise. I am almost certain, though, that this is not what is happening to me. I usually clear my self to the lowest possible altitude directly, which in this case is 2500 ft (and set the MCP altitude accordingly. I know it is not the most realistic, but I am still learning to deal with the stress of an approach :-)). However I still see the problem occuring. I will try another test later... Also, I will have to check what I have set in the styles menu...Thanks for the informative input, Mats :-waveBoazEKCH

I'm going to fly back to base now EDDL-EGLL. Will see if I can do the descend correctly this time. :-jumpy