Modifying FMC crz level can cause actual CLB&DES while in VNAV PATH mode in 747 ???
I just experienced an unfamiliar thing during yesterday flight.
While i was in VNAV PATH Cruise at FL350, i modified FMC Flight level to FL349 with expecting "VNAV ALT". However what i've really seen was the A/C did actual descent to FL349 without changing FMA(was Still VNAV PATH). Furthermore, after i modified to FL350 again, A/C started to actual climb to resume FL350.(with almost 500~700 fpm)
I tried to figure out why this thing happened from FCOM but couldn't find it.
it has been my common sense that FMA should have to change to VNAV ALT if there is any difference MCP target alt with FMC VNAV crz alt.(in VNAV mode)
any idea?
p.s: "TD"was not even close at that point.(it was around 200NM away)
and this thing did not happen when i tried to modify to FL340.(FMA changed to VNAV ALT)
Last edited by FlywithPark; 9th Jun 2013 at 12:56.