VNAV question for Randy

[KevMac 0]

Hey Randy -I was going to just reply to the other thread we had going on this issue, but wasn't sure if you would miss it, so here's a new one :-)Okay, it appears the 250kts speed restriction is defaulted up to 10,000ft by the FMS (on "ECON CLB" page or something like that). In your latest example, you posted a picture showing a 215kt restriction, which seemed to work just fine. Now, I am assuming the 250kts restriction should work by default (no reason to re-type this in as it's already there.) When I took off on my last flight, I used TO/GA for initial thrust setting, climbed to around 1500ft and hit the VNAV button. The VNAV button turned on, and appeared to be working (still without the CMD button on), but then the airplane once again exceeded 250kts within 2 to 3 thousand feet, and seemed to be moving towards it's normal post-10,000ft CLB mode speed, which is well above 250kts. Shouldn't VNAV adhere to restrictions even when the CMD button is off?Thanks again,Kevin

[crvm 0]

Honestly I don't know if the use of VNAV can be used on the NG without a A/P engaged. Frankly I cannot find any reference for this. Unlike what you see, my plane will not follow the VNAV profile without CMD engaged. I know one guy claimed one can use VNAV but he did not seem to be talking about a RW NG but only what he was taught on. It could be wrong here, will have to have a NG pilot comment on this one or someone with fact from a AOM or something other than " I know it does". My FMS trainer for the classic will not engage VNAV without a CMD engaged. It does keep it fine with CMD engaged....http://forums.avsim.net/user_files/89218.jpgBest Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/Animation1.gifCaution! Not a real pilot, but do play one on TV ;-)AMD 64 3200+ | ASUS KV8 DELUXE | GFORCE 5700 ULTRA @535/1000 | Maxtor 6Y080M0 SATA 80 GIG | 512 DDR 400 | Windows Xp Pro | Windows Xp Pro 64 |

[Mike S KPDX 598]

no, it will not fly without the CMD mode engaged. The flight director does not care who is in control, you or the AP - all it does is direct the flight via the indicator on the PFD.On my install, the ADI will display the correct pitch in VNAV if VNAV is indeed selected ON and the FD is selected ON.

[crvm 0]

Interesting, I believe the 744 will infact engage VNAV without selection of CMD but the NG appears to be different if Mike is correct. Like I said, I am not sure here but there are pilots about who fly the NG who can straighten this out with 100% certainty...Best Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/Animation1.gifCaution! Not a real pilot, but do play one on TV ;-)AMD 64 3200+ | ASUS KV8 DELUXE | GFORCE 5700 ULTRA @535/1000 | Maxtor 6Y080M0 SATA 80 GIG | 512 DDR 400 | Windows Xp Pro | Windows Xp Pro 64 |

[744pilot 0]

Thats true Randy, In the 744 you can ingage the LNAV and VNAC on the ground already. (LNAV is also possible in the NG, to arm on the ground) The B744 also is possible to engage the AP as soon as possible and it will maintain V2+10 until accelaration height, which my the NG is not possible because as soon as you engage the AP it does start to excelarate.BTW. Nice signature you have. :)

[Guest Taz]

Mr. SmithWhat is this FMS trainer you speak of?ThanksSteve

[Guest boxjockey99]

GuysSpeaking from real world experience on the classic here is how we fly an LNAV/VNAV departureTOGA V1, Vrotate etc400ft - Engage LNAV1000ft or at min noise alt - Engage VNAVPassing 170kt flap 1Passing 190 flap upVNAV will maintain 250kt up to FL100 unless the restriction is deleted in the CLB page. VNAV will do this whether the A/P is engaged or not. As has been stated previously the Flight Director is the brains of the system not the A/P. To simplify the system completely the A/P blindly follows what the Flight Director bars tell it to do. You in turn tell the flight director what to do via the MCP or via the FMC/CDU. So whether the A/P is engaged or not you still have control over what the Flight director is doing. The way that this thread reads seems to me that the pilot in question simply expects the aircraft to fly itself once VNAV/LNAV are engaged, this is not the case if no A/P is engaged then YOU must drive the bus. I may have read this wrong but that is how it reads. The key is to see where the magenta speed bug is driven to when VNAV is engaged. It should drive straight to 250kt then passing FL100 drive to ECON climb speed (around 300 ish) then to ECON Mach then cruise mach! If it drives straight to the 300ish mark then it has ignored the FL100 restriction for some reason! If I have got the wrong end of the stick then please let e know and explain it to me in a different way then I can see if I can help! RegardsKris

[zubart 5]

> Honestly I don't know if the use of VNAV can be used>on the NG without a A/P engaged. >>Best Wishes,>[h4]Randy J. Smith[/h4]>http://www.rawbw.com/~bdoolin/shinault/Animation1.gif>Caution! Not a real pilot, but do play>one on TV ;-)>>AMD 64 3200+ | ASUS KV8 DELUXE | GFORCE 5700 ULTRA>@535/1000 | Maxtor 6Y080M0 SATA 80 GIG | 512 DDR 400 | Windows>Xp Pro | Windows Xp Pro 64 |Yes, in the real world you can fly with Vnav engaged in FD (Flight Director) mode after 400 feet AGL. Floyd

[KevMac 0]

Thanks Kris!Since Kris cleared some things up for us here, my next question is obviously WHY is my NG exceeding 250kts under 10,000 while in VNAV? My 250kts/10,000ft is defaulted in the CLB page.. Per Kris, I should not be exceeding the restriction while in VNAV even without CMD engaged.Thanks!Kevin

[Guest gremel]

Kris,At what point do you engage the A/P during the climb mode?? I don't think you said in your post. Also, does the PMDG 737 NG 700 series LNAV & VNAV function like the real thing. The reason I'm asking this question is that I have a chance for some [level D] 737 NG 700 series or 800 simulator time and I want to practice take-offs & landings. I don't want to do something that the real sim does but the PMDG doesn't....Can you identify these areas? I'am currently flying the PMDG 700 series and have not as yet upgraded to the 800...Should I in view of the upcoming level D opportunity or will the 700 satisfy realistic functionality..If you could, please outline the progressive steps that you take on a normal takeoff up to FL100.. Thanks & regards,Jack

[crvm 0]

"The way that this thread reads seems to me that the pilot in question simply expects the aircraft to fly itself once VNAV/LNAV are engaged, this is not the case if no A/P is engaged then YOU must drive the bus. I may have read this wrong but that is how it reads." Sounds like Chris is in agreement with me that without CMD you must fly the bus. Correct Chris? Although the classic and NG are different, this of course depends upon what FMC update the particular airplane is using. Jack, while Chris is always of help, he does not fly the NG so maybe cannot speak 100% to what this does compared to what he flys. Mr. Brad Marsh could answer your question better simply because he does fly the 800 NG for Pacific Blue (Virgin Airlines).....Best Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/Animation1.gifCaution! Not a real pilot, but do play one on TV ;-)AMD 64 3200+ | ASUS KV8 DELUXE | GFORCE 5700 ULTRA @535/1000 | Maxtor 6Y080M0 SATA 80 GIG | 512 DDR 400 | Windows Xp Pro | Windows Xp Pro 64 |

[zubart 5]

Hey Kris, Just want to add,The airplane can be flown with with F/D's off and autopilot on.I'm not sure what kind of an ADFS a -300 has but in the NG the duel ADFS system consist of two FCC's (Flight Control Computer's). This would be the brains.For A/P operation, they send control commands to their respective pitch and roll hydraulic servos, which operate the flight controls through two seperate hydraulic systems.For F/D operation, each FCC positions the F/D command bars on the repective attitude indicator.Floyd

[Guest quietwing]

KevinI believe your NG is exceeding 250 kts under 10 000' because you are not following the pitch command on the flight director. You probably need to increase your nose up attitude. As Kris stated VNAV is a pitch mode, it still requires the pilot to manually adjust pitch when not using autopilot. The thrust does not vary to maintain 250 kts. Hope this helps, keep asking if it doesn'tHans

[Guest tmetzinger]

In my experience, if you follow the command bars on the flight director with VNAV on but the autopilot off you will maintain the proper speed profile. Where most folks get the overspeed is by not maintaining a high enough climb angle, and since in a VNAV climb mode the autothrottle is set to the appropriate climb setting, PITCH CONTROLS AIRSPEED.So, try it with the fright director and keep that pitch angle up.

[crvm 0]

Thanks everyone for clearing this up ;-)...Best Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/Animation1.gifCaution! Not a real pilot, but do play one on TV ;-)AMD 64 3200+ | ASUS KV8 DELUXE | GFORCE 5700 ULTRA @535/1000 | Maxtor 6Y080M0 SATA 80 GIG | 512 DDR 400 | Windows Xp Pro | Windows Xp Pro 64 |