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744 - VNAV engaging doesn't work

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Have an issue when engaging VNAV mode.

FMC is setup properly. Climbing speed (ussualy 320kts/0.83) and crussing speed are setup. F/D (Flight director) is on. A/T (Auto thrtole) is on.

I start to climb and when I switch to VNAV mode each time is automaticaly rejected. VNAV buton automaticaly deselect after a 1 second following by appearance of 100 kts speed on speed window

When I reach targted altitude, then correct Command Speed is shown on Primary Flight Dispay and VNAV mode can be engaged.

Also on PFD, Airspeed Indication bar doesn't showing Maximum Maneuvering Speed margin, nither the Minimum Maneuvering Speed margin. That is permanent foult, which doesn't affect on aspect of flight.


Could somebady be so kind and help.





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What is the altitude set to on the MCP ?


When you try to engage VNAV in climb you must be below any altitude restriction for the next waypoint in the FMC legs page.


What did you set the speed window to before takeoff? It needs to be set to V2.

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First, thanks for the answer. Appreciate.


The altitude set on MCP is the same as on the FMC.

For  example, if I climb to the cruise altitude of 35000, same is set on FMC and MCP.


Each time when engage VNAV i am always below any altitude restriction/altitude set point in the FMC.


Before takeoff, I always set V2 or sometimes V2+10kts.


Anyway, thank you on the reply

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