I've seen long haul pilots use the FIX part of FMC to show suitable alternates on ETOPS flights.

Can someone talk me through how they do this and what it all means? Many thanks

How you do this depends on your aircraft, your FMC, your company's procedures, and your preferences. There's not just one way.

The big picture is that you are trying to increase your situational awareness, so you always have good information at your fingertips as to where you will divert should the need arise. 

One thing people commonly do is enter the equal time point (between two alternates) as a fix in the FMC. Prior to that fix, go to the first alternate if anything happens; after that point, go to the second. However, before you can do this, you'd need to get the equal time point from your flight plan--you can't enter it as a fix unless you know it. Then simply create a fix by typing in the latitude and longitude of your equal time point.

Another way people do it is to enter your alternate airports as fixes, and optionally draw rings around them (how you make the rings appear depends on your model of FMC, and whether your flight instruments have a map feature), with the point being you can see which airport is closer at any given time, and get precise distances and bearings. Entering airports is simpler than entering equal time points, since you just need to type in the name of the airport and you don't have to worry about latitude and longitude. 

Again, how you actually do this depends on your aircraft and your FMC.

Edited May 5, 20242 yr by prolixindec