Altitude

[Zimmerbz 166]

When selecting an altitude in the FMC, how does it determine what my maximum FL is?  I was doing a flight that my flight plan was selected to be 380.  When I entered everything and got to the page to select my altitude, it said my max was 340.  How does that get factored in?  Does it have to do with my CI?

[JoeDiamond 67]

It has to do with several things.  Aircraft weight, temperature, and planned speed are the primary factors.

[Budbud 227]

Hi,

For such a discrepancy, I would check particularly the GW of the aircraft (and especially the unit, KG instead of LBS and vice-versa) and the TOC temperature and ISA entered on the perf init page (a wrong temperature entered here can really mess up the FMC calculations!).