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Guest David Ketchum

PMDG 747-400 Engine Out very messed up, yikes.

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Guest David Ketchum

Hi Guys,This may be a FS2004 limitation and perfectly understandable, but the Engine Out procedure in the FMC with the PMDG 747 is completely unrealistic. The programming logic in regard to FMC/VNAV operation during an engine failure apparently gets completely flustered if the autopilot is left engaged, and will eventually stall the aircraft. The FMC then starts to spit out two different max altitudes for E/O ops? Basically, everything just goes beserk. Again, this may be a limitation, but the manuals supplied with your product basically spells out that the FMC engine out page and VNAV intregation upon engine failure works realistically? It would be cool if you all could simply state the E/O feature is not modeled in the sim because otherwise people like me spend quite a while trying to get it to work properly. Just a thought! Cool sim though.-David Ketchum

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Guest David Ketchum

Ok, played around a little with some engine out scenarios at cruise altitude. What I'm seeing is that that the PMDG sim will give a correct realworld single E/O altitude readout on the regular FMC VNAV CRZ page upon sensing engine failure. When I select the E/O page, however, the maximum cruise altitude for single E/O is listed MUCH lower than realword figures. Why this built-in discrepancy from PMDG?Well, realworld engine out at cruise altitude ops in a 747-400 involves setting max continuous thrust with the three remaining good engines and maintaining level flight until the aircraft decelerates to the published E/O drift down airspeed, then commencing driftdown to max single E/O altitude. This process yields the slowest loss of altitude over distance and is standard procedure.The PMDG 747, however, cannot maintain the realworld drift down altitude even with three engines throttled up to max con thrust. The aircraft will continue to decelerate and eventually stall. This of course is not realistic. Maybe something to do with FS2004's goofy air density logic at high altitude? So, to compensate, the PMDG engine out page on the FMC displays a very low single E/O altitude (in comparison to realworld figures), which, if maintained, will allow level flight at a reasonable LRC airspeed with three engines only. I think what it amounts to is that the PMDG 747 can't really model anything close to engine failure performance figures at high altitudes and is limited in this regard to engine failure at or below 10000 ft or so, at least in respect to realworld 747 numbers. This explains why the FMC engine out page is not modeled correctly I think. Am I anywhere close to hitting the nail on the head with this one guys?Thanks!David Ketchum

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Guest A32X

Hi David,I just failed the #1 engine at FL350, Gross Weight 235.5 tones, and the FMC gave me a max engine out altitude of FL288 however I could maintain FL350 comfortably, not needing MCT. What I did notice though was the aircraft remained balanced with no rudder input... Paul

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Guest David Ketchum

Hi Paul,The scenario I used was takeoff in the 747F at max gross weight (875,000) pounds. My initial FMC optimum altitude with 4 engines running was approximately FL310. Upon failing number 3 engine, the main FMC VNAV page now displays a max altitude of FL280 (I wonder if this is a 'generic' engine out altitude with the PMDG FMC). No way will it maintain this altitude with only three engines at max con thrust. When I select the VNAV engine out page, the FMC curiously now displays a max engine out altitude of 14,500ft approximately, along with a optimum altitude of 7000ft??? I don't get the discrepancy between FL280 and 14,500ft when switching between the main VNAV and Engine Out VNAV pages or the calculated engine out optimum altitude of 7000ft? Weird.Although I don't have performance tables for the 747-400F, I really can't believe that max single engine out altitude even at MTOW would be 14500ft, yikes. What's obvious is that the PMDG FMC VNAV engine out page is not integrated with autoflight in the PMDG 747 as it is in the real aircraft. One must manually input the correct performance figures into the autopilot and bypass the FMC altogether. I realize that now, but I'm just wondering if the FMC engine out page is supposed to be displaying actual calculated performance or is just spitting out generic data. Again, my dilemma is that PMDG doesn't talk about this lack of functionality in their FMC, yet the PMDG manuals makes inferences that FMC engine out works realistically. I did a thread search on this topic and found that a couple of people concurred on my observations, yet no one from PMDG answered their questions on the same subject. The whole issue would seem a little taboo or something, and it's like PMDG would rather sweep everything under the rug?It's really not a huge issue with me, I'm thrilled with my purchase and really enjoy the 747 sim. I bought both versions (regular and cargo), and consider this the best add-on purchases I've made, bar none. So I'm not cruising for flame responses or dissing PMDG in any way, fashion or form; it's just that there seems to be a black hole in information regarding this subject and nobody 'officially' responds or talks about it. A simple acknowledgment from PMDG that this is a known issue would be cool so that users don't waste time trying to figure out what they are doing wrong when they try to use the FMC as dictated by the PMDG manuals. Not too much to ask is it guys? :)Have a great day,-David Ketchum

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Guest David Ketchum

Ok, in lieu of not having access to a real 747-400 performance table for engine out max altitudes, I can only speculate that the PMDG FMC engine out altitude is purposely lower than realword in order to compensate for FS2004 air density modeling weirdness at high altitude. The E/O altitude that PMDG FMC will display is one that the PMDG flight model itself can handle. Again, this is only speculation, but since PMDG is apparently never going to address this issue(?!), my observation will have to stand as gospel. Unless of course PMDG would like to step in and correct me...........Nevertheless, my modified E/O procedure for the PMDG 747 is as follows: 1) at engine failure, manually select max con thrust on the FMC thrust management page. Pay no attention to the max altitude message that the FMC will now display on any page EXCEPT the VNAV engine out page. Only the VNAV engine out page will display the correct engine out altitude required for the PMDG flight model, and this is what you need.2) select the VNAV engine out page. Note the displayed max engine out altitude and E/O driftdown airspeed figure(s).3) dial in the VNAV engine out max altitude figure into the MCP ALT window.4) press the speed knob on the MCP to engage speed intervene mode. Dial in the airspeed figure displayed on the VNAV engine out page. Failure to engage speed intervene with the calculated driftdown airspeed figure will result in VNAV accelerating to the regular all engine VNAV PTH cruise airspeed and subsequently descending too rapidly for a normal driftdown.5) press the MCP altitude knob to execute a controlled driftdown. VNAV will advance power as needed to maintain E/O airspeed (via speed intervene), and the aircraft will be descended to the altitude selected on the MCP (max engine out altitude). The aircraft will maintain a constant -1200 ft/min rate of decent until the modified cruise altitude is reached, then the PFD should annunciate SPD VNAV PTH. The new cruise altitude will be modified automatically in the FMC VNAV engine out CRZ page to whatever is manually set on the MCP altitude window (this should be the calculated max engine out altitude).This procedure differs from the real 747 in that speed intervene mode must be used on the PMDG 747, and the -1200 ft/min decent rate PMDG uses would otherwise be around -300 ft/min on the real aircraft. In addition, the real 747 will automatically select max con thrust and also automatically select the max engine out altitude into the FMC. This all has to be done manually on the PMDG. Yes, I realize I'm a genius! Comments/critiques/etc solicited. Oh and PMDG? You guys can say something too, don't be shy ok? :)-David Ketchum

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David,Do you have the 400F addon? I know EV did some work on engine out with one of our 400 Captains on the test team for that... It's not possible to get it 100% right due to FS limitations but I think we got closer than just about anyone with the final 744 code post 400F.


Ryan Maziarz
devteam.jpg

For fastest support, please submit a ticket at http://support.precisionmanuals.com

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David,Read with great interest your remarks stated above. The FMC quoted MAX ALT figures are straight out of the manufacturers manual. Where do these "real world" figures you talk about come from ? Reference please ? Volume, page, publisher ?Regarding asymetric behaviour, thrust required, d/d rate etc we had two certified people checking all this independently and thoroughly. One of them was/is a test pilot for this type. Probably contributed to the aforementioned manuals... Even the rudder trim index required is almost identical. Regardless, since obviously you saw what you saw and 7000 is rather ridiculous (I agree) I wonder whether other sim issues came into play. Try no weather please ?Best,Vangelis===================================== E. M. Vaos Precision Manuals Development Group www.precisionmanuals.com=====================================


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E M V

Precision Manuals Development Group

====================================

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