Ah yes, its clearer now, Thank you Sir !
SFC is lowest when operating in high pressure, high density air. (You will probably find that your performance notes are wrong on this matter.)
..Now that makes sense !...
On the effect of altitude on endurance the manual says
" For a Jet at Vmd increasing altitude does not effect the drag, but the engine SFC improves, giving greater endurance" (until of course you go above the Optimum Altitude and air compression becomes an issue).
>So in reality does (T)SFC increase with altitude... and would i be correct in saying that as a jet airliner cruises at a high altitude , its engine efficiency actually decreases (due increase in sfc) , but its aerodynamic efficiency increases (thrust does not get too high due to the low air density).. and Overall the aircraft is more efficient at higher altitudes ??
Thank You..