expat wrote on Feb 10^th, 2017 at 12:14pm:

SOLVED: Just to report back, I finally got a moment to test this and yes it worked and captured the loc and gs. I believe it was also not having the EFIS set to APP and possibly also I was arming the APP button too late. Engaging it around 10nm rather than closer (in the green arrow on the GPS) may also been the problem.  Thanks for your help!

It has nothing to do with setting the EFIS to APP mode. I rarely use APP mode on the EFIS, yet the 777 captures the LOC and Glide Slope. If it doesn't capture the GS, it's usually because I have pressed APP on MCP (AP) after the aircraft has dropped below the GS (usually because I have forgotten to press it in time)!