amber EFOB msg in A320 ...

[ppppilot]

IflyI. Be more specific on your queries and you will obtain more exact answers.
I understood from your opening post if amber msg in the fms it is a legal advisory to declare emerg or taxi back to the ramp.
Later you pointed more in that way, saying to kindly ignore the first two lines of the post.
Nothing to see with running out of fuel. Pay attention to the second phrase in my post… As long as you land with …
Further from that…
If you are talking about how to make your best fuel predictions. Do not consider the fms your ONLY source of information. Give to your paperwork a chance.
In an 11 hrs. flights when I reach the first crz fl, the first thing I do is check systems and fuel. I compare actual burned off with that I have on my operational flight plan OFP. Even with all the data perfectly introduced into the fms and the latest winds downloaded from the acars, the FMS ETA and EFOB at destination use not to match with OFP. The deviation can be big so as to produce an amber msg. At that point your experience must talk. As flight goes by, both FMS and OFP gets closer on predictions.
I am used to deal with the best flight planning software at the companies where I have flown. One of the best soft is the Lufthansa Lido. http://www.lhsystems.com/topic3/topic33/ . It is tighten, like the nuts of a german submarine, to real. It is difficult to get a hundred kilos in or out from the lido at the end of the flight. But to be honest I must say I have not used it on long haul flights.
Finally. I may deduce from your latest words that you are talking about the use of contingency fuel. This is a very common question and there are thousands of discussions in pprune and all over the internet. Query for Indian regulations first and after do a search on contingency fuel. You will read thousands of experiences on that.
Tailwinds