I recently purchased EFB and wanted to pass on some tips related to runways and scenery in FSX and EFB.   I too was having problems with the whole runway.txt thing and getting EFB to recognize runways I had installed within FSX.  I did review the Forum FAQ (Runways.txt / Runway identifiers are greyed out), the documentation within the runway.txt document itself, and scoured the forums.  I was utimately able to figure out what the issue was and corrected it. So I thought i would share my discov