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Guest tiffernine

Unable to arm LNAV on take off

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Guest tiffernine

Hi,Everything is settled perfect for take off, FMC route is ok. To arm VNAV works, but LNAV is not possible to arm ?Does anybody have an idea ?Thanks for your adviceAlfredLOWW

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>Hi,>>Everything is settled perfect for take off, FMC route is ok.>To arm VNAV works, but LNAV is not possible to arm ?>>Does anybody have an idea ?>>Thanks for your advice>>Alfred>LOWW>>I don't believe you can engage LNAV until you are above 500 feet, and the A/P is on. Remember you must be on an intercept course for LNAV to engage.Someone please correct if I'm wrong.- John


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- John Drago

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Guest Hawkeyeted

John,In the 747-400, you can arm the LNAV and VNAV prior to T/O. The FD should give you Pitch/Roll cues after rotation, with the ability to engage CMD above 400ft AGL.That said, I'm not sure why the original thread author is unable to arm LNAV. Works fine for me.....

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>John,>>In the 747-400, you can arm the LNAV and VNAV prior to T/O. >The FD should give you Pitch/Roll cues after rotation, with>the ability to engage CMD above 400ft AGL.>>That said, I'm not sure why the original thread author is>unable to arm LNAV. Works fine for me.....Thanks for the correction. I do arm VNAV prior to t/o, but only engage LNAV once I'm airbourne. Just a matter of my procedure.- John


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- John Drago

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Guest Hawkeyeted

John,I learned of it in a funny way too. I was watching the ITVV Cathay B747-400 video when I notice the captain armed them both as he was positioning onto the runway. I immediately fired up FS9 with the Queen. Low and Behold, I could do the same thing. However, I'm with you in that I "usually" T/O in HDG HOLD or HDG SEL specifically if the departure is a vectored DP. Once on track I then engage the LNAV. Arming LNAV works wonderfully if you have immediate paths to follow after T/O (i.e. Rome Fiumicino is an example).

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Guest afluhart

I've noticed that you have to have a departure rwy selected in the FMC. Thats what worked for me when I had the same problem.

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LNAV has certain criteria before it can be armed. I cannot recall off hand but one part is to be "within" 3 NM of the course and I think on an "intercept" course to the path...[h4]Randy J. Smith[/h4]AMD 64 4000+|ASUS K8V DELUXE|SAPPHIRE ATI X800XT PE|MUNCHKIN 3200|80 gig SATA|DELL 1905FP 19" LCD|TRACKir PRO|PFC JEPPESEN MOONEY YOKE|CH PRO PEDALS|


Randy J Smith

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Guest Hawkeyeted

>> LNAV has certain criteria before it can be armed. I cannot>recall off hand but one part is to be "within" 3 NM of the>course and I think on an "intercept" course to the path...>True....if you're already inflight. The problem here was the inability to arm while on the ground (i.e. positioning on the active, arm VNAV/LNAV if so desired.)

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Hi all,The thread starter didn't mention which aircraft he's flying, and there may be some differencies. But for the 737NG:LNAV criteria on ground: - origin runway in flight plan - active route entered in FMC - track of first leg within 5 deg of runway heading - LNAV selected prior to TO/GA. Once TO/GA is engaged, the LNAV switch light is extinguished until 400ft AGL; * LNAV guidance becomes active at 50ft AGL * bank angle is limited to 8 deg below 200 ft and 30 deg above 200 ft AGLLNAV criteria in flight: - active route entered in FMC - within 3 NM of active route, LNAV engagement occurs with any airplane hdg - outside 3 NM the airplane must: *be on intercept course of 90 deg or less *intercept route segment before active waypoint

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Guest tiffernine

Hi all,the reason was,I forgot to select the take off runway in the FMC (PMDG 747)Thanks for your advice.Best regardsAlfred

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