Pressing FLCH / VNAV on the ground.

[heinz92]

From what I gather, it is never done on the ground. My question is, would pressing FLCH or VNAV on the ground also activate TO/GA and advance throttles in the real aircraft like it does in the IXEG? Or are other reasons why you should never do it in a Classic? I know it is a hypothetical question but I'd greatly value anyone's input with knowledge! Thanks!

 

[Eddie]

Depends on the software revision. IXEG has modeled an earlier version where VNAV could not be modelled on the ground, but later updates added this functionality. NGs were the same way until they also got the aforementioned update.

[heinz92]

But theoretically, on these older software model FMCs, would the throttles advance and take the aircraft to the air, or would it just not engage? 

[Litjan]

When you press FL CHG or VNAV the autothrottle enters a "combined mode" - in most cases it will set climb thrust (N1) to fly the airplane to the next desired altitude. Try this - put the MCP altitude to below the aircraft and then click FL CHG. You will see that the autothrottle enters the combined mode of "retard - idle" and tries to descend.

So yes, on the older software FMCs the throttles would advance to N1 limit thrust, and if the pilot is a total fluke, it would "take the aircraft to the air" (unless buildings or trees are in the way)

The autopilot has no idea wether you are on the ground or not, you can even see it trying to fly a turn if you engage HDG SEL when you engage CMD on the ground...

Jan

 

Edited July 26, 2016 by Litjan