I'm sorry if this does not answer your question(s) greenband, but you've not worded them very clearly:
Anyway here goes:
1.
My first question is normally a computer flight plan ( Jeppesen and many others) are based on "ECNO" speed mode or "LRC" speed mode ?
Normally a computerised (or manual for that matter) flight plan will be based on whatever the flight planner/ crew decide and select when the plan is being created. That can mean anything from fixed MACH, LRC, MRC, a company standard speed or even ECON (no such thing as ECNO??).
Factors that will influence the choice range from route/ schedule/ timings/ payload/ fuel cost ......
2.
If wind modifications, wind mixing and winds and step climbs and Cost Index are conducted during cruise, which speed mode should pilot select on VNAV page ?
Whatever is appropriate! You should note that COST INDEX relates to ECON speed. A flight plan produced using ECON as the default will have been produced with a specific COST INDEX associated. This cost index would normally be input to allow ECON to default correctly. It can of course be modified as appropriate to adjust timing etc.......
So a crew will input the appropriate speed mode on the climb/ cruise/ descent page as per the flight plan.
3.
I understand that "ECNO" is a defult mode for FMC, if forecast winds for fuel remain at destination is necessary to re-calculateste, LRC and MCP speed mode will have the this functions?
I'm sorry, but this question simply does not make any sense? Can you rephrase it and I will try to answer it for you?
B