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Ray Proudfoot

Flying a SID with the FMC

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Simon,Many thanks for creating these files. I'll fly back to Manchester and see how the aircraft copes with that 180 turn from 26L.Whilst I have your ear could you modify your EGCC files to remove the altitude constraints up to SANBA please (plus any other SIDs out of EGCC with similar constraints)?As Pete pointed out the initial clearance is up to 5,000ft so if you could set that for SANBA the earlier waypoints should have their altitudes set by the FMC automatically.Thanks,


Ray (Cheshire, England).
System: P3D v5.3HF2, Intel i9-13900K, MSI 4090 GAMING X TRIO 24G, Crucial T700 4Tb M.2 SSD, Asus ROG Maximus Z790 Hero, 32Gb Corsair Vengeance DDR5 6000Mhz RAM, Win 11 Pro 64-bit, BenQ PD3200U 32” UHD monitor, Fulcrum One yoke.
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Tony,I wish I could do that at work. :-) I bagsie No 1 :-lolCheers,


Ray (Cheshire, England).
System: P3D v5.3HF2, Intel i9-13900K, MSI 4090 GAMING X TRIO 24G, Crucial T700 4Tb M.2 SSD, Asus ROG Maximus Z790 Hero, 32Gb Corsair Vengeance DDR5 6000Mhz RAM, Win 11 Pro 64-bit, BenQ PD3200U 32” UHD monitor, Fulcrum One yoke.
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Hello RayI'll modify both files over the next couple of days, to sort the altitude constraints, back to work tomorrow:(Simon

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Thanks Simon, much appreciated.Cheers,


Ray (Cheshire, England).
System: P3D v5.3HF2, Intel i9-13900K, MSI 4090 GAMING X TRIO 24G, Crucial T700 4Tb M.2 SSD, Asus ROG Maximus Z790 Hero, 32Gb Corsair Vengeance DDR5 6000Mhz RAM, Win 11 Pro 64-bit, BenQ PD3200U 32” UHD monitor, Fulcrum One yoke.
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Ray,I think that you may have misunderstood Anthony's explanation. What I think he was trying to say was that your problem has nothing to do with setting your MCP altitude to 5000 feet. The problem is that you have speed contraints for your first 3 waypoints (evidenced by the large font) with corresponding altitude constraints. The altitudes shown for those waypoints are FMC predicted altitudes (as evidenced by the small font), based on the 3000 ft contstraint at the fourth waypoint. Remove the speed constraints at the first three waypoints, and you should not have any trouble with 5000 (or 35000 for that matter) set in your MCP window. (Note: I don't know what the SID requires, so I can't comment on what changes might be necessary to comply with the SID.)In a climb, the FMC will honor the lower of the MCP altitude or the VNAV altitude constraints. It would unnecessarily add to pilot workload at a busy time if the pilot were required to match the MCP altitude with the altitude constraints. Normally, the MCP altitude would be set to the cleared altitude.Anthony, I couldn't find the reference in the manuals to the issue of VNAV disconnects on encountering a speed constraint without a matching altitude constraint.Don S.

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As a new user, and knowing two of the combatants :-) here I followed this thread with interest and mounting confusion, thanks for clarification Don ;-)I could not understand why VNAV would disconnect if the MCP had a higher altitude set than the FMC commanded, this going off my familiarity of the DF737 and PIC767 but your explanation cleared that up.However I guess that still leaves the question of speed constraints, I suspect Simon put those in so that the A/P could manage the sharp turns. If the speed/altitude constraints don't work how would you automatically limit speed, or would it be by manual intervention?So new and so much to learn :-)Dave Wild

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Hello DaveVNAV will disconnect if only a speed constraint is entered and no altitude constraint.I haven't entered any speed constraints in the sids I have done. I have entered altitude constraints, which seem to be causing problems. The 3000ft constraint on the HON1R/1Y sid from egcc, at HON58 or SANBA-5 (its the same point)is 3000 or above. I have set the constraint at 3000 here as the above feature isnt operational yet. And then later 5000 at SANBA.It should be possible to take off with an initial cleared altitude of say FL100 set in the MCP, select LNAV and VNAV and fly the sid until SANBA at which point VNAV should continue the climb to FL100.Important though dont set speed constraints against the waypoints that dont have alt constraints set.Flap settings will keep the speed down under VNAV and help around the initial turns.Hope this helpsSimon.

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> If the speed/altitude>constraints don't work how would you automatically limit>speed, or would it be by manual intervention?>Dave,I don't think the manual speed intervention in VNAV works yet in the PMDG FMC. I think I read somewhere that they will be providing it in a later update. If you want to stay in VNAV you have two choices: 1. Keep your flaps extended - VNAV will limit speed according to the flap retraction schedule, or 2. Insert the limit speed as either the speed restriction speed or the target climb speed in the VNAV climb page of the FMC.Don S.

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Hi Don,Thank you for the explanation. You are right - I had misunderstood Anthony's explanation. This message, together with replies from my other posted query last night, have given me a new insight into how the FMC works on the PMDG737. Previously I had assumed that it worked quite closely to the 767PIC. Clearly this is not the case.To sum the rules up. Inputting a speed OR altitude constraint without including the second parameter will cause the FMC/MCP to function incorrectly. Include both or rely on calculated values and all will be okay.I understand the significance of large and small fonts in the FMC. What I hadn't appreciated is the impact on the FMC. Elsewhere the point was made that speed is limited by flap setting. So 240/6000 for a given waypoint will not be achieved if flaps are extended.Quite a different beast to the 767PIC isn't it?Thanks,


Ray (Cheshire, England).
System: P3D v5.3HF2, Intel i9-13900K, MSI 4090 GAMING X TRIO 24G, Crucial T700 4Tb M.2 SSD, Asus ROG Maximus Z790 Hero, 32Gb Corsair Vengeance DDR5 6000Mhz RAM, Win 11 Pro 64-bit, BenQ PD3200U 32” UHD monitor, Fulcrum One yoke.
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>Quite a different beast to the 767PIC isn't it?>Hi Ray,It certainly is! It's not quite to the same level of simulation yet, but they're getting there.As far as the speed/altitude constraint issue goes, it is not necessary to enter a speed constraint for every altitude constraint. However, as presently programmed by PMDG, it is necessary to enter an altitude if you have a speed constraint. As Ian Riddell pointed out in the other thread, in the real world 737NG FMC, this is not necessary.I also question whether the real 737NG FMC has a better way of dealing with your issue of selecting a cruise speed that is much higher than the target descent speed. I don't have an NG FMC manual handy to check right now, though.Don S.

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Hi Don,it is not necessary to enter a speed constraint for every altitude constraint. However, as presently programmed by PMDG, it is necessary to enter an altitude if you have a speed constraint.Blimey! That's going to take some memorising. I'll have to write it in large letters and nail it to the monitor!:-eekAs Ian Riddell pointed out in the other thread, in the real world 737NG FMC, this is not necessary.Then why, if PMDG are trying to emulate a real 737NG, do they not program it the same way? :(


Ray (Cheshire, England).
System: P3D v5.3HF2, Intel i9-13900K, MSI 4090 GAMING X TRIO 24G, Crucial T700 4Tb M.2 SSD, Asus ROG Maximus Z790 Hero, 32Gb Corsair Vengeance DDR5 6000Mhz RAM, Win 11 Pro 64-bit, BenQ PD3200U 32” UHD monitor, Fulcrum One yoke.
Cheadle Hulme Weather

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Guest amerton

>Then why, if PMDG are trying to emulate a real 737NG, do they not program it the same way? :(The world is simple, isn't it ?Bulfer's 737FMC guide states VNAV disengages on speed only constraints. page 79 in May 98 ed:"Speed constraint entries require an altitude constraint at same wpt for VNAV to remain engaged"This being said, I'm waiting for a confirmation this is only valid for the Honeywell FMC, not the Smiths FMC... I'm also waiting for confirmation that this is not the case on the Smiths U10.4 FMC (because I have the doubt this "constraint" was removed in software release 10.5 only). We model the 10.4 release.Would this be a - sort of - satisfactory explanation on why things are the way they are ?anthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

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Guest Ray CYYZ

Anthony, just a little extra headache in the mix here:Even when flying with both a SPEED & ALT set, if you bounce through the height, you are still going to get kicked out of VNAV because you are now above the constraint. Since SID flight is likely to have rather excessive climb rates, is there a possibility of building in some slop factor?The FMC does the proper thing by kicking VNAV off and giving a CHECK MCP ALT message because you are above the constraint during the climb phase, but it is not an intentional thing by the pilot, it is an overshoot due to the grossly overpowered NG :-lolAm I making sense? :-hmmmRay

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Guest amerton

You are... there is a slop factor as we speak... off the top of my head 150 feet...I would suggest : derate your TO thrust, using TO2 for instance...Am I making sense as well ? }(anthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

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Yep, I had to learn this the hard way. FLY THE PLANE! If you are light and are shooting up like a rocket there is no way to really expect VNAV to stay engaged. This happens in the real world too, in fact all the time... I know I am making sense =)[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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