B777 LNAV vs LOC
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B777 LNAV vs LOC
Reading the Normal Procedures chapter in Vol 1 regarding IAP using VNAV .
Can you use LNAV for a LOC approach and if the answer is no can someone explain why not. Also the Vol 1 Chapter SP - "RNP" states that the FMCS meets the requirements of a multi-sensor RNAV system when RADIO or GPS is updating, and in this configuration the FMCS may be used for ENR, TERM OPS and IAP Navigation - excluding ILS, LOC, LOC-BC,LDA,SDF,MLS. In this case can you explain why LNAV is mentioned so many times in Vol 1 IAP using VNAV.
Thanks
Can you use LNAV for a LOC approach and if the answer is no can someone explain why not. Also the Vol 1 Chapter SP - "RNP" states that the FMCS meets the requirements of a multi-sensor RNAV system when RADIO or GPS is updating, and in this configuration the FMCS may be used for ENR, TERM OPS and IAP Navigation - excluding ILS, LOC, LOC-BC,LDA,SDF,MLS. In this case can you explain why LNAV is mentioned so many times in Vol 1 IAP using VNAV.
Thanks
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I have (flying a 738 NG) started to use LNAV instead of LOC during NP-LOC approaches since it is much more stable. The autopilot don't have to chase the localiser all the time.
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As technique I use LNAV to establish on the LOC if its a large intercept and select LOC once established. It makes a smoother join with less of an overshoot. If you are flying an NPA to LOC minima then LOC should be selected, it is more accurate. Using LNAV you can see quite a localiser deflection in some instances.
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Desertcamel,
I don't see any reference on why you couldn't use LNAV to fly a LOC approach, as a matter of fact the NP section states that: for a LOC, SDF, bla-bla approach the recommended roll mode for final approach are: LNAV or LOC . I agree with the personal technique to intercept the LOC in LNAV especially if it's a large inercept angle, but I personally would track it in LOC mode, since that is the most accurate, and even the FMC goes into LOC-GPS updating when it has a valid Localizer signal associated with the destination runway, below 6000 feet, less than 20 NM from the navaid, withinn such and such degrees, the exact number I can't recall, therefore your LNAV track is updated to the Localizer anyway... So you can use LNAV if you so desire, works fine, just make sure that you don't parallel the Localizer....
As for the second part of your question, I think they ment to write it as including ILS, LOC, SDF, etc, but I'm not quite sure, tried to read it 3 times now, and can't get my head around why couldn't you use it for all those approaches...
I don't see any reference on why you couldn't use LNAV to fly a LOC approach, as a matter of fact the NP section states that: for a LOC, SDF, bla-bla approach the recommended roll mode for final approach are: LNAV or LOC . I agree with the personal technique to intercept the LOC in LNAV especially if it's a large inercept angle, but I personally would track it in LOC mode, since that is the most accurate, and even the FMC goes into LOC-GPS updating when it has a valid Localizer signal associated with the destination runway, below 6000 feet, less than 20 NM from the navaid, withinn such and such degrees, the exact number I can't recall, therefore your LNAV track is updated to the Localizer anyway... So you can use LNAV if you so desire, works fine, just make sure that you don't parallel the Localizer....
As for the second part of your question, I think they ment to write it as including ILS, LOC, SDF, etc, but I'm not quite sure, tried to read it 3 times now, and can't get my head around why couldn't you use it for all those approaches...
