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Ray Proudfoot

Early descent problem with FMC

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Hi all,I fly the PMDG737 using Radar Contact as my controller. The ToD using RC occurs earlier than the calculated ToD on the PMDG737 FMC. So when RC orders me to descend I have to comply.Although I'm able to do this via the Des Now option on the Des page the following message is then displayed...http://forums.avsim.net/user_files/39606.jpgI'm unable to clear this message. Even if I want to enter a flight level against a particular waypoint so the descent path is then achievable I can't. From this point on the FMC becomes unusable.Is this a feature of the real B737-700 or is it a bug in the PMDG737? If it's meant to happen like this how can I enter data into the FMC?Cheers,

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Ray, Here is what Captain Bulfer says:"After the descent is active, the FMC predictions show the profile constraints at the nexy wpt cannot be made and the Path maintained. Displayed If the required flight path angle to meet the next altitude constraint exceeds 7 degrees for aircraft operation when more than 1000'above the airport speed restriction altitude; otherwise 6 degrees. VNAV will disconnect (CWS)... Modify the LEGS or DES page plans re-engage LNAV and VNAV"[h4]Best Wishes,Randy J. Smithhttp://img.villagephotos.com/p/2003-8/196432/winglets_lg.jpg [h3] AMD XP 2200 |MUNCHKIN 512 DDR RAM |ECS[/b ][i] K7S5A MB[/i] |GF2 MX 32 MEG and still runs GOOD!|WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"[/h3]

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Randy,Sorry, I haven't a clue who Captain Bulfer is. However...<>What precisely should I modify? I can't change any of the altitudes - the permanently displayed message prevents any further input. Even moving up the 2nd active waypoint to become the active waypoint doesn't solve the problem - the message stays displayed and nothing I can find will shift it. Surely this can't be right? The CLR button should clear the message but it doesn't. It should, shouldn't it?Try it yourself. 30 miles before the calculated ToD start your descent early. The message will soon appear and if you manage to clear it please advise how you did it.Cheers,

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Well that's the thing, you are going by RC 's TOD and not the FMC's TOD. What does DES NOW do? It starts an early descent (at appx 1000 FPM)UNTIL it CAPTURES the original calculated PATH. But this is not what you want it to do? Try LVL CH, once you are close to the path you can try to re engage VNAV but seeing that you are 30 miles prior I doubt it. Captain Bulfer is a 737 pilot who is also the author of the FMC User's guide and the Big Boeing Book used by real world pilots and hard core simmers ;)I am not sure why you cannot clear the message. [h4]Best Wishes,Randy J. Smithhttp://img.villagephotos.com/p/2003-8/196432/winglets_lg.jpg [h3] AMD XP 2200 |MUNCHKIN 512 DDR RAM |ECS[/b ][i] K7S5A MB[/i] |GF2 MX 32 MEG and still runs GOOD!|WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"[/h3]

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Randy,<>I tried LVL CH but the aircraft dropped like a stone to maintain the airspeed. So I had to revert to a manually controlled descent using VS. But all this is somewhat irrelevant.Why won't the message clear when the CLR button is pressed? I'm not complaining about the FMC not controlling the descent properly as I'm happy doing that myself. All I want is some way to input or amend data in the FMC for future waypoints and as things stand I can't.If you have access to the official 737 manual does it say there that the message stays on permanently? If it does then I'll accept that the FMC is modelled accurately. Otherwise it's a bug that needs resolving please.Cheers,

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"I'm not complaining about the FMC not controlling the descent properly " Well Ray it does descend correctly but you must stay within the limits of what its designed to do, just to clear that up ;). I use DES NOW all the time and it works like a charm. Anyways to your problem, the message should NOT stay there once you clear it but you cannot even clear it. Why not is a good question. Let me investigate this further. [h4]Best Wishes,Randy J. Smithhttp://img.villagephotos.com/p/2003-8/196432/winglets_lg.jpg [h3] AMD XP 2200 |MUNCHKIN 512 DDR RAM |ECS[/b ][i] K7S5A MB[/i] |GF2 MX 32 MEG and still runs GOOD!|WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"[/h3]

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Hi Ray, I always use Radar contact as well. I know it's cheating but, since I know that RC is going to ask me to descend 30-40 miles before my Flight Plan does I just ask for a Deviation for turbulance and then clear it when I'm at my flight plan TOD. As long as your down to 10,000 feet 40 miles from the airport then the rest of the RC altitudes will agree with your flight plan. When I asked in the RC forum why the descents were so early the answer was that it was based on a generic to all aircraft descent rate. Like I said it's cheating a bit but still better than getting chewed out by Bill Stevens from FSDO. :-lolWilliam Shedd

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Hi William,Cheat? CHEAT?? I couldn't possibly do that :-) In any case it's easy to be at 10,000ft 40 miles out. It's been ages since I last missed that restriction. I didn't miss the restriction on that particular flight either.Bill won't chew you out for missing the crossing restriction but I agree that it's better to prevent a telling off at the end of the flight.Cheers,

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Hi Ray,I am also using all the time Radar Contact.Usually, when I'm instructed to start the descent, I stop using the VNAV and I set the speed and V/S for descent.Sometimes I's setting the speed and the I use LVL CHG, but it seems that sometimes it switches automatically to N1 and starts a nose dive which sometimes is very difficult to recover....As for the message that it is not deleted, try pressing the CLR key many times. It happens to me many times, on long flights, when the FMC will start saying Insufficient Fuel (even if it happens to reach at destination with something like 10-15.000 Lbs). It seems that the messages accumulates somehow and they have to be cleared one by one.Also, my FMC displays the TOD time as being after the estimated time of arrival at destination, even if the distance to TOD seems to be 'correct' (less than distance to the destination airport. This is happening all the time, no matter how long the flight it is.Regards,Marius

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Hi Marius,<>That is how I controlled my descent on a flight today from LFMN (Nice) to Manchester (EGCC). Perfect all the way down and curiously I didn't get the Des Pth Unachievable message.<>Tried that many times but to no effect. I can always clear the Insufficent Fuel message but this one is either being deleted and instantly redisplayed or the FMC isn't responding to the CLR button. Which one is it PMDG?It adds to my growing suspicions that it is an occasional bug. Some response from the PMDG developers would be appreciated here. I'm grateful to Randy but he doesn't have access to the source code.<>You'll also find the calculated fuel is wrong as well. Hopefully PMDG are aware of this are the forthcoming patch will cure it.Despite poor frame rates with the 2D panel and a few remaining bugs this aircraft has many more plusses than minuses. PMDG are getting there.Cheers,

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Where do you have your AdvDisplay placed on the panel? I've tried various places and am currently using the wide part of the center post under the compass. Wish they would move the letter buttons that open the various panel windows to the bottom. They would look a lot better there, not to mention, that would be a great place for the AdvDisplay. All and all though, the PMDG 737 and Radar Contact make a good combo. John Fitzpatrick

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John,I have a second monitor which comes in very handy. I use ShowText in preference to AdvDisp. It's displayed permanently on the 2nd monitor. If your graphics card can support two displays consider getting one. Not just for ShowText of course but the ability to have panels such as the FMC undocked and permanently visible is very handy.Cheers,

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I've had a similar occurence.Man-LGW Sid ex Man Hon1R into Astra Star 26L Flight planned at FL260, I requested descent from FS9 ATC cleared FL150 and given a radar heading after about 3 mins into the descent. At the time I had VNAV & LNAV engaged with Econ path descent. I got an FMC message next alt unachievable and then try as I may I could not clear the message, although i could use the line select keys I could not cancel the message. I was using 737NG with standard FS9 no other add ons.hope this helps.

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I'm bumping this up the list as I haven't had a response from PMDG. I've taken the time and trouble to post this problem which I believe is a bug. A reply would be appreciated - thanks.

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Ray,I cannot reproduce.The flight plan and cruize alt and where you started the descent would help.Please mail amerton@precisionmanuals.comThanksanthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

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Hi Anthony,Thanks for joining in. This was a flight from Malaga (Spain) to Manchester (England) and is nearly 3 hours in duration. I wouldn't expect you to fly that long trying to reproduce the problen I encountered.I'll setup a shorter flight and see if I can reproduce the problem on that. If I do then I'll send the relevant files to you together with relevant instructions on how to reproduce it. My descent (as dictated by Radar Contact) started roughly 40 miles from the calculated PMDG ToD.Cheers,

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