PPRuNe Forums - 737NG LNAV on take off

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Vessbot

15th August 2025 23:15

737NG LNAV on take off

I noticed that shortly after 50 feet, (that is, after FMA "LNAV" changes from white to green) the light in the LNAV button in the MCP extinguishes for a few seconds and then comes back on (all the while, the FMA LNAV stays green).

Does anybody know why?

FlyingStone

15th August 2025 23:49

The change of AFDS roll mode is inhibited between 50 and 400ft RA. The philosophy is that if the light is illuminated on the MCP, you can press the illuminated button, which will deselect the currently active mode. No light = can't deselect.

TheBusFlyer

17th August 2025 21:47

Never seen this on the 777. Is it only on the 73?

aerostatic

30th August 2025 02:57

Quote:

Originally Posted by TheBusFlyer (Post 11940280)

Never seen this on the 777. Is it only on the 73?

Yes, I believe that's correct. On 737 you can deselect any MCP mode except for APP. On FBW Boeing on can't deselect any mode except for APP (above 1500').

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