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mrdfw

Why would TO/GA disarm VNAV, used fine previously,,,,?

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Are you going around from an RNAV approach? I'm not in front of the FCOM now, but I recall that that is the correct behaviour. If I recall, VNAV will re-engage above 400ft agl. Perhaps I'm mistaken on the specifics, but this sounds about right. Trouble is, I don't fly RNAV approaches that often. Trevor Edit: Thinking about this a bit more closely, I think you might actually have to manually reengage VNAV once flaps are up to the desired position. Again, I'll have to check the FCOM to be sure. You might consider looking there as well. I recall the Automatic Flight section of the FCOM2 being very detailed in its description of the go-around logic.

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yeah but I've been taking off from the same airport at least ten times never had to reengage RNAV either this just started happening to me as well at some random point.

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The only time the VNAV mode will be disarmed is when the TOGA switch is pushed during approach when the radio altitude is less than 2000 feet and the A/P is not in flare arm.

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I think he means when you arm TOGA for take off the V nav light shuts off . this is going on with me also. I have to put it back on after take off. It never did it before.Now it is going off every take off when I engage TOGA.What,s up with that?

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I think he means when you arm TOGA for take off the V nav light shuts off . this is going on with me also. I have to put it back on after take off. It never did it before.Now it is going off every take off when I engage TOGA.What,s up with that?
It should have always done that...the armed modes will "disappear" when TO/GA is selected at take off and will automatically become active at 50' AGL (LNAV) and 400' AGL (VNAV) if armed prior to TO/GA being selected and the lateral criteria being met for LNAV pre-takeoff arming. This is the correct behavior.Adam

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It should have always done that...the armed modes will "disappear" when TO/GA is selected at take off and will automatically become active at 50' AGL (LNAV) and 400' AGL (VNAV) if armed prior to TO/GA being selected and the lateral criteria being met for LNAV pre-takeoff arming. This is the correct behavior. Adam
The PFD will still annunciate that they are armed but the switch lights will go out. Also worth noting that to arm LNAV on the ground you must have an active route in the FMC.

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The PFD will still annunciate that they are armed but the switch lights will go out. Also worth noting that to arm LNAV on the ground you must have an active route in the FMC.
Yeah...sorry, just couldn't come up with the right words. But that is what I meant. If the criteria for arming VNAV and/or LNAV is met on the ground, they will continue to be annunciated on the FMA in white but the lights on the MCP will extinguish when TO/GA is selected. Adam

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