737NG LNAV on take off

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15th August 2025 | 23:15

#1 (permalink)

Vessbot

Thread Starter

Joined: Sep 2016

Posts: 937

Likes: 67

From: USA

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?

15th August 2025 | 23:49

#2 (permalink)

FlyingStone

Joined: Apr 2010

Posts: 1,320

Likes: 102

From: IRS NAV ONLY

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.

17th August 2025 | 21:47

#3 (permalink)

TheBusFlyer

Joined: Mar 2020

Posts: 31

Likes: 1

From: Paris

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

30th August 2025 | 02:57

#4 (permalink)

aerostatic

Joined: Dec 2000

Posts: 70

Likes: 0

From: Off track, again

Quote:

Originally Posted by TheBusFlyer

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').