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JSACKS

Can VNAV land you properly ?

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I've never landed any Boeing a/c in VNAV. With the NG, I've always joined the LOC and dropped LNAV, and then captured the GS and dropped VNAV. This evening, however, I flew into KSFO 28L and let VNAV+LNAV handle it. I approached at the speed of my penultimate waypoint, IAS 155, which was too high and it exceeded the Vref speed of 138 by some margin; 138 was also written into the FMC for RW28L (or it got written in at some point on the approach, dropping from 155). But at 500 AGL (or rather, above water!), I disconnected the AP and hand flew her in because it seemed the SPD was not going lower than 155. I landed fine.Is the SPD for final approach supposed to drop to the Vref+5 automatically if you keep VNAV active with the AP? How do you actually land in VNAV?Appreciate any advice on this, thanks!Jonathan


Jonathan Sacks

Dell XPS Gen 4, Pentium IV Northwood extreme 3.8Ghz, 3Ghz RAM, eVGA 7900 GTO,

12 GoFlight modules plus MCP-PRO AP and EFIS, GF pedestal, CH rudder pedals,

CH throttle quadrant, 42" LG LED, 24" DELL LCD, Windows XP, FS2004, FSUIPC 3.96

FS Autostart 1.1 (Build 11), FS Navigator 4.6, UT, FE, GE, REX, PMDG, Level-D, PSS, etc.

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Guest neeraj.pendse

I do not think you can do an A/P approach without being in the APPROACH mode ... so I really do not understand where you are coming from? If you are in approach mode, The VREF is clculated by the FMC, but you have to manage speeds/ deceleration yourself on final approach. At least that's what I think on the PMDG.On the PSS Airbus, I have noticed that when you "activate approach mode" the plane automatically drops to a slower speed, and you can extend flaps one by one and the speed reduces to a new value automatically. After the last notch of flaps, the speed settles to VREF. - Neeraj

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Guest FattyBear

If you are talking about doing a full CAT3 autoland with VNAV then no, you can't. Those can only be done using ILS.

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Not from what I have experienced. The FMC does indeed reduce speeds to the waypoint restrictions all the way down including the approach path where one would normally be on the LOC and the GS. VNAV descended me stably with no APP function active but was descending me a tad rapidly and I would have landed short and too fast. I am certainly no expert in VNAV but I was curious whether there is a method to get VNAV to land you 'cos I was not far off from doing that tonight. I see Alex says it can't be done and maybe it can't although I was sure I had previously seen screenshots of one or two others landing in VNAV, but maybe I was just hallucinating. Jonathan


Jonathan Sacks

Dell XPS Gen 4, Pentium IV Northwood extreme 3.8Ghz, 3Ghz RAM, eVGA 7900 GTO,

12 GoFlight modules plus MCP-PRO AP and EFIS, GF pedestal, CH rudder pedals,

CH throttle quadrant, 42" LG LED, 24" DELL LCD, Windows XP, FS2004, FSUIPC 3.96

FS Autostart 1.1 (Build 11), FS Navigator 4.6, UT, FE, GE, REX, PMDG, Level-D, PSS, etc.

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>I've never landed any Boeing a/c in VNAV. You have to define better what do you mean by "landing in VNAV". You mean being in VNAV how low? To the runway? This is a very ambigous question.Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2http://www.precisionmanuals.com/images/forum/747400.jpghttp://www.hifisim.com/images/asv_beta_member.jpg


Michael J.

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Guest glenb

Jonathan,A while back I did a lot of work with VNAV/LNAV approaches. Approach plates identified with RNAV (GPS) RWY xx are for that type approach. The minimums listed will be for LANV/VNAV or just LNAV.My experience is that I have been able to use LNAV/VNAV for some runways and not others. It has always been a question why. These approaches are the future and there are several web sites that explain them. A search of this forum for VNAV or RNAV should provide a lot of information.In my opinion the FMC in the PMDG does not follow the path as it should. It seems that at times the pitch will not follow the descent path. There are several items to consider: a low cost index seems best, remove any altitude restrictions such as 250/7000A to 250/7000 the A means cross at or above at 250kn. Even with these considerations there will be problems. The manual says that you must be at flaps 15 before 15 miles from the airport. See page 10

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I don't think VNAV as implemented in Boeings was ever meant for LNAV/VNAV approaches of today world. To fly those semi-precision and precision LNAV/VNAV approaches you need WAAS certified GPS receivers. VNAV in 737 can get you at most to standard MDA on non-precision approaches but this is just a level-off step-down aproach so whether one uses VNAV or LVLCH is of little importance. However some 737NG with some airlines are capable of flying really special RNP-RNAV aproaches (Alaska Airlines pioneered them) and these are truly remarkable approaches. Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2http://www.precisionmanuals.com/images/forum/747400.jpghttp://www.hifisim.com/images/asv_beta_member.jpg


Michael J.

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Guest tmetzinger

>I don't think VNAV as implemented in Boeings was ever meant>for LNAV/VNAV approaches of today world. To fly those>semi-precision and precision LNAV/VNAV approaches you need>WAAS certified GPS receivers. VNAV in 737 can get you at most>to standard MDA on non-precision approaches but this is just a>level-off step-down aproach so whether one uses VNAV or LVLCH>is of little importance. However some 737NG with some airlines>are capable of flying really special RNP-RNAV aproaches>(Alaska Airlines pioneered them) and these are truly>remarkable approaches. >Absolutely untrue. WAAS may be required for LPV approaches (which give you ILS-like tolerances to a very low decision altitude), but for LNAV/VNAV approaches all that's required is RNP-0.3 performance, which the 737NG does easily (RNP-0.1 is common on NG models). The advantage of flying an LNAV/VNAV approach is a constant glide path instead of the "dive and drive" path that may result by using VS or LVL CHG.As others have noted, when "soft" constraints are used the VNAV performance is variable. To fly a LNAV/VNAV approach, one should use the approach chart and modify the fixes and speed/altitude constraints accordingly. Remember that your SID/STAR and approach data is from MILITARY sources (DAFIF) and may not match the approach profile shown on your approach chart - so FIX IT.The autopilot will fly the appropriate path assuming you stay on top of the speed - common mistake is not being configured for landing by the final approach fix and being too fast for the final segment.However, once you reach the decision altitude (hopefully on speed), you need to land manually (use the autothrottle for speed control if you wish). You're supposed to do the same thing on CAT I ILS approaches as well.Best Wishes,

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Yes, all the way down to the runway--that was the question as I intended it if it was not clear. In other words, leave the LNAV and VNAV functions totally on coupled to the autopilot all the way down to the ground. That was what I was experimenting with on my flight into KSFO. It was purely an item of curiosity because I've never really known whether VNAV was supposed to be capable of doing such a thing. In any event, it seems to be that one does not by and large land in such a manner (thanks, GlenB for your post). It's not a critical item to me, I am just interested in exploring the envelope of the NG's FMC capabilities to the extent that I am capable of doing so myself !Jonathan


Jonathan Sacks

Dell XPS Gen 4, Pentium IV Northwood extreme 3.8Ghz, 3Ghz RAM, eVGA 7900 GTO,

12 GoFlight modules plus MCP-PRO AP and EFIS, GF pedestal, CH rudder pedals,

CH throttle quadrant, 42" LG LED, 24" DELL LCD, Windows XP, FS2004, FSUIPC 3.96

FS Autostart 1.1 (Build 11), FS Navigator 4.6, UT, FE, GE, REX, PMDG, Level-D, PSS, etc.

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Tim,The other day I took the PMDG 737NG - 600 into Belfast UK Int A/port and did a full Cat III autoland all the way down to the runway in App mode with Vnav and Lnav engaged all the way. From what you say in your last sentence this is not realistic - or did I misundestand? Are you saying that while the a/craft can do it, procedurally it is wrong?RegardsIain

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Guest Moviedirector20

No what you did is fine. There are different categories of ILS, I, II, III, IIIa, the difference being DH, and a = autoland. In an ILS I the autopilot can fly to the DH (usually 200 RA) then the captain/FO disconnects it (Auto-throttle may still be used) and lands manually. The advantage to II,III is lower DH so that if your plane can take it then you can land in worse weather. IIIa is used in extremely low RVR (runway visual range) conditions, it has no decision height I believe. It will land the plane even if you cant see the rwy.my 2 cents, I may stand corrected.

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>runway in App mode with Vnav and Lnav engaged all the way.You can't be both in APP and in LNAV/VNAV at the same time (both engaged as 'green'). APP is for the ILS approaches when your horizontal mode is LOC and vertical is GS. LNAV/VNAV approaches have nothing to do with the ILS. Look at your PFD and see what horizontal/vertical modes are engaged at the moment. Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2http://www.precisionmanuals.com/images/forum/747400.jpghttp://www.hifisim.com/images/asv_beta_member.jpg


Michael J.

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You cannot VNAV all the way down to the runway (autoland). What you can do is a VNAV approach where you disconnect and take manual control at a certain Decision Height (DH) above the ground. If you can't see the runway and perform a manual landing upon reaching the DH, you execute a mandatory go-around. Again, VNAV is not an autoland - if you want autoland you must use a dual or triple channel coupled approach in APP mode.


Ryan Maziarz
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Iain:Can you possibly describe how you programmed the FMC for the approach and touchdown. How did the speeds for final approach get set into the FMC? Also, the descent path?Jonathan


Jonathan Sacks

Dell XPS Gen 4, Pentium IV Northwood extreme 3.8Ghz, 3Ghz RAM, eVGA 7900 GTO,

12 GoFlight modules plus MCP-PRO AP and EFIS, GF pedestal, CH rudder pedals,

CH throttle quadrant, 42" LG LED, 24" DELL LCD, Windows XP, FS2004, FSUIPC 3.96

FS Autostart 1.1 (Build 11), FS Navigator 4.6, UT, FE, GE, REX, PMDG, Level-D, PSS, etc.

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