crvm,
when FMA says FMC SPD, it really means that i.e. speed control from FMC. therefore, to alter the speed, just enter a new speed in your FMC CLB page.
although, FMA says ALT HOLD, it is still considered as in VNAV as your VNAV on MCP is still engaged, right? therefore, an alternate method is to exit VNAV by hitting ALT or FLCH thereby opening the MCP speed window giving you manaul speed control.
hope this helps...
SR
ps. i dont fly the NG but the 777, but i reckon the AFDS is pretty much the same. it's a boeing, ain't it?
