Boeing 777 engine-out cruise question

[fireball_23]

Hey guys

Just a quick question. Looking at the engine inoperative cruise technic in my manual, I've noticed a big difference when VNAV is engaged, and when it's not.

With " VNAV not engaged " :

- Select CLB/CON on MCP
- Select a lower altitude on the MCP
- Select FLCH and disconnect the A/T

Why would you disconnect the A/T right away in FLCH and not in VNAV ?

Sorry if the question seems stupid, or maybe I just miss a key point here, but I can't figure why..

Thanks !

[BuzzBox]

With VNAV engaged, the autothrottle will maintain MCT for the driftdown descent. With FLCH engaged, the autothrottle will reduce thrust - that may not be desirable if terrain is a factor.

[ACMS]

Better be quick disengaging the A/T after you select FLCH or it will close the thrust before you can blink!!

Why not select CLB/CON first, wait a sec while the Thrust advances then disconnect A/T, then select FLCH?

[Gillegan]

Why not select CLB/CON first, wait a sec while the Thrust advances then disconnect A/T, then select FLCH?

When you select FLCH, the A/T's will re-engage so you'll have to disconnect them again anyway.

[fireball_23]

That makes sense now. Thank you so much for your help !