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Guest Marc Sykes

A few issues with SU 1.1

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Hello all,I've owned the 737NG for several weeks but haven't posted here previously since the only real problems I had were with VNAV and I was waiting on the update. So ...First, excellent job with the patch. Accurate fuel predictions, no more dives--really glad to see this. So here are two relatively minor problems I had on an initial flight from San Francisco to Los Angeles:For whatever reason, my speed during cruise was set at 295 KIAS, which translated to about M 0.71 at FL270. Before it had always shot for 315 KIAS/M 0.755; interestingly, when I looked at the LEGS page, this was the setting for all the waypoints once I reached cruise altitude-- M.0755/FL270. Yet on the CRZ page, under speed, it said 295 knots, and that's where VNAV held it throughout. I did derate the climb, since I was light on fuel, but did I accidentally derate the cruise? Or is that even possible? This is more likely something I did wrong (or it may simply be better VNAV logic--it could well be that M0.72 is more practical at a lower altitude), but it never happened before SU 1.1; regardless of climb speed the NG would always jump up to M 0.755 once I hit cruise altitude.Second, I flew the SADDE6 arrival into LAX, and mostly left the waypoints and constraints as they are on the FMC. My first constraint was SYMON and I amended it to 280/12000, which is most often given by ATC, instead of 290/12000 which the FMC had. The next constraint after that is BAYST at 240/10000 (set by the FMC in accordance with the STAR chart), about 13 flying miles. VNAV started me on descent perfectly at the T/D, kept me on the path perfectly while managing speed (didn't even have to use spoilers) until SYMON, but upon reaching SYMON abruptly disconnected with the message "UNABLE NEXT ALT." I thought this was odd; it shouldn't have been difficult to get down 2,000 feet in 13 miles and slow down a bit (real 737s do it all the time) and if it needed a bit of extra drag it could have said so and I would have hit the spoilers. Any thoughts on why it would simply disconnect with UNABLE NEXT ALT? I had already reset the MCP altitude to 7,000, which is the restriction for SMO, the final waypoint, so it can't be that.The only thing that might be connected, I suppose, is that I had gotten a couple of INSUFFICIENT FUEL messages when I was programming the FMC in San Francisco. My ZFW was 108,330 lbs., and I took 10,000 lbs. of fuel; the FMC predicted I would land with 4,400 pounds remaining. However, as Fred Clausen's excellent tutorial flight recommends, I entered "Reserves" as 5.2 (5,200 lbs), so perhaps that's why it was telling me INSUFFICIENT FUEL? Still, VNAV shouldn't disconnect halfway through my descent just because I'm dipping into my reserve fuel, should it?Speaking of which, anyone working on a fuel planner for this bird? I've been spoiled by the PSS planes where you can just input trip length, cruise alt, winds etc. and it spits out the exact perfect amount of fuel to take. With this guy it's all guesswork, though I'm mostly operating on what Fred wrote in the tutorial, which as I recall is that 5,000 pounds is about an hour's worth of fuel. That's why I figured 10,000 would be way more than enough for SFO-LAX.Thanks for any help you can provide. By the way, we should do some 737NG group flights on VATSIM like the PIC-heads do!Regards,Marc SykesSenior VP, LAX OperationsPacific West AirwaysZLA ARTCC Senior Student

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Hello Marc,Just want to mention I had a similar experience flying from KPSP to KLAX (Palm Springs - Los Angeles). I had the same UNABLE NEXT ALT error and VNAV DISCONNECT flying the Paradise Four Arrival at the SUZZI intersection. Passing Arnes at 11,000 and descending to Suzzi at 9,000. I had the arrival pre-programmed from the Jeppesen plates, so I was flying an exact descent profile. I must admit the patch is an improvement, but I thing we still got some problems.....

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Gents,If you can provide me with some additonal data, I think I might be able to help or explain (or do some fixing for the next update, if needed).I'd need the complete flight plan file, the sidstar files, the cruize alt, TO / fuel weight and every possible additional detail I forget to mention.Also, I need to know what in flight amendements to the FP you've done, if any.One possible reason I could imagine is the aircraft undershooting the constraint and going beneath the tolerance, meaning the aircraft would be under the constraint, causing (logically) the unable next alt.There are complex interactions between the FMS and the AP involved, and I'd really like we tune all this like if it is was a Swiss cuckoo clock ;-)So please email additional info to amerton@precisionmanuals.comTIAanthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

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Marc,Look at the CLB CRZ DES pages targets. I changed the 315 to lower speed in 1.1, to be more in line with LVL CHG (and VNAV SPD) descents.There has been a post by Terry (who converted the DADIFF data in procedures) that some of his sidstar files would position intercept positions wrongly, resulting in legs of several thousands of miles. Please check the FP to see if it's the case. This could explain the insufficient fuel message.As for the unable next alt thing, please check out my post in reply to Stuart's post.Thanks !Anthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

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Not to sure but please keep this in mind: During the climb, VNAV complies with the legs page waypoint altitude constraints. A temporary level-off for a crossing altitude restriction is accomplished at the current commanded speed.When the climb speed profile causes an anticipated violation of a waypoint altitude constraint, the FMC displays the CDU scratchpad message UNABLE NEXT ALTITUDE. A different speed profile that provides a steeper climb angle must be manually selected...Waypoint speed constraints take priority if slower than the target speed...OVERSPEED DISCONNECT:U10.3 and later: During path descent and above or below the speed restriction altitude, VNAV disengages when airspeed exceeeds FMC speed restriction by more than 15 knots.Action- Manually reduce speed and reengage VNAV.UNABLE NEXT ALTITUDE:U10.4 and later: Unable to meet the next flight plan altitude constraint in a VNAV climb or descent. The message appears only with VNAV engaged. ACTION- Clear the message and review the prediction. For undershoot condition during climb, consider selection of MAX RATE CLB or MAX ANGLE CLB, or a different N1 limit as appropriate.[h4]Best Wishes,Randy J. Smith [/4]P M D G 7 3 7 NG[/h4]http://img.villagephotos.com/p/2003-8/196432/mineimage.jpg [h3] Realism on the horizon 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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"OVERSPEED DISCONNECT"Big thanks for that one Randy. I am used to getting a "Drag Required" message telling me the bird needs help, not a disconnect abort.I was going in and replacing the /315 with a /250 and getting kicked out of my chair by my force feedback stick when the autopilot executed this abrupt disconnect.Knowing that all I need to do is step it down in 15 knot increments and not have to pick myself up off the floor is great!Ray

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My only thought with the PDZ4 scenario is that there's only 4 miles between ARNES and SUZZI; that's not very far to descend 2,000 feet. So I can completely understand the UNABLE NEXT ALT in that situation. Looking at the chart (I have all the LAX charts in a binder because I control there), you can actually cross ARNES anywhere between 10,000 and 11,000 feet. (And SUZZI at or above 9,000 feet; most of the constraints on this arrival are there not to get you down but to keep you above certain altitudes so you don't interfere with departing traffic in the area.) The previous waypoint is TEJAY at 12k and there's 9 miles between TEJAY and ARNES, so if you do TEJAY at 12, ARNES at 10, then SUZZI at 9, it will probably work. If that isn't how the STAR is programmed in the database, it should be.However, that still doesn't explain why my 737 didn't feel it could descend from 12k to 10k in 13 miles, which should be more than enough room. I will try the flight again or another one like it, but offhand I can't think of anything that would be non-standard; I flew the STAR exactly as the 737 FMC had it except that I crossed SYMON at 280 knots/12k instead of 290/12, but if anything that would help with a subsequent descent. I know there weren't any misplaced fixes or 1,000 mile legs; actually, even after VNAV disconnected I kept LNAV on until crossing Santa Monica, at which point I disengaged the autopilot completely and flew the Stadium Visual approach manually.As for the fuel, like I said before I had 10,000 pounds on departure, making my TOW 118,330. My predicted fuel on arrival was 4,400 pounds and at this particular point in the flight I think I had 4,700 or 4,800. So I was dipping into my reserve fuel (I had set reserves to 5,200 pounds on the INIT REF page.) I wouldn't be surprised if this was what caused the INSUFFICIENT FUEL warnings but I'm wondering if it had anything to do with the VNAV disconnect? It makes a strange sort of sense, I guess, if the FMC didn't think I was going to have enough fuel to have engines running at the next constraint, that hence I would not "make" that altitude.I'm not exactly sure what you mean by undershooting the constraint, Anthony. And from what I could see most of what Randy posted related to climbs rather than descents. I guess I will just keep trying and see what happens.Regards,Marc Sykes

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Hi,The patch is excelent til now, except the fact that in FS 2004 the aircraft is still bouncing all the time in climb, cruise, or descend, well, when AP is ON. I tried also to disable joystick when in flight and it doesnt help. Do you know any solution?Coimbra

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The UNABLE NEXT ALT etc applies in either climb or descent Marc. See here is the issue, since we cannot tell the FMC to MEET at or below right now (although constraints will work most of the time) we must use other means to get the job done. You could keep LNAV going and go LVL CHG or V/S to meet restrictions. Or if you did not manually set 12000 on the legs you could have set 12000 on the MCP which would cause ALT HLD at 12000' and after passing that waypoint resume VNAV and set 10000' on the MCP etc. It might not be the way you want to do it but will work.[h4]Best Wishes,Randy J. Smith [/4]P M D G 7 3 7 NG[/h4]http://img.villagephotos.com/p/2003-8/196432/mineimage.jpg [h3]Moving forward one step at a time 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, And by the way just see this screenshot: 15000 feet at the altitude, and VNAV still continues climbing ...Any solutions?Coimbra

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Marc,I just made another flight KPSP-KLAX. Reprogrammed the Arrival with ARNES 250/10000 SUZZI 240/9000 and got a VNAV DISCONNECT before I even got to ARNES.... Last FMC message was DESC PATH UNACHEIVABLE...Surely a 737 can fly this Arrival without crapping out....Regards,

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What are your framerates running at? I certainly had some issues when I overdid things and had framerates hitting less then 15. Seemed like the autopilot was simply falling behind due to not enough processor time.Ray

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Hi, Another one. Computer and FS closed due to "system run out of memory" which means not enough resources to run applications. Well, I have 1024 DDR 333 and just FS was opened ...Any solutions?Coimbra

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I find it best to try running any panel with frame rate slider way up at ~75, then I note where frame rate caps out. I then set my slider to ~75% of that value to allow the processor some headroom. If you see frames dropping more than 2-3 fps below your max framerate setting on a regular basis, the CPU is maxxed out, and smoothness in A/P, video etc is likely to be affected with otherwise minor variations in CPU loading.Smooth frames at 18 fps is far better than spastic at 30.RegardsBob ScottATP IMEL Gulfstream II-III-IV-V L-300Washington, D.C.

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You make it sound like VNAV disconnect does not happen in the real world that often?? A 737 can fly it but you are flying the bird and not being there (you provide no screenshot) to see what is going on. That message happens for one reason only and it is this: CAUSE: When in path descent and above the path, the FMC predictions show the profile restrictions at the next waypoint cannot be achieved (LNAV remains engaged).CORRECTIVE ACTION: Modify the restrictions So please post a screenshot so we can look at the instruments and your path deviation at the time this happens....[h4]Best Wishes,Randy J. Smith [/4]P M D G 7 3 7 NG[/h4]http://img.villagephotos.com/p/2003-8/196432/mineimage.jpg [h3]Moving forward one step at a time 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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Ryan, The above post of mine is from the AOM, VNAV does disengage although you still have LNAV engaged. Your dad is right and this is what most NG pilots do also. The whole idea is to lesson your workload and that being the case it's sometimes more simple to go LVL CH or V/S than to program the FMC...[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, Anybody available to explain me the 2 or 3 issues I asked ?thankscoimbra

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Hi, I still continue with the same problems reported. Anyone to explain?Coimbra

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Just to comment the fuel planning stuff...I use the manual to plan trip fuel, but you always have to plan taxi fuel, minimum reserve fuel, enroute reserve and alternate reserve fuel...I use a standard reserve of 2600lbs...Bit too much (same as 767 pilots use) but still...Enroute reserve in head wind flights: 1900lbs...Taxi is around 3000lbs...And alternate differs but could be around 5000lbs...So that's well sufficient reserve fuel, even if the trip is longer or you burn more fuel than expected, you still have more than 5000lbs left when on final...Hope that helps a bit, but please use the amazing charts for trip fuel planning in the PMDG manuals!Boaz...

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Just so this doesn't turn ugly :-) We are aware that this happens on some installations and are looking into this problem. RegardsPaul Gollnick :-coolTechnical Operations/Customer Operational SupportPrecision Manuals Development Groupwww.precisionmanuals.com

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Randy,>>Your dad is right and this is what most NG pilots do also.<If the VNAV is programmed correctly

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