There was a problem with the flight tracking today. I was tracking my son’s flight (UA 197) from IAD to SEA. The non-stop flight time duration was to be 5hr 40 min. After 3hr3min, Flight aware had the flight line ending at the ND/SD border, and stating the flight had reached the destination. Needless to say, I was in a panic for the next 2 1/2 hr., until I was able to verify that the flight had safely landed in Seattle. What was the problem???
This is a known issue. Please see
discussions.flightaware.com/view … t=tracking
I realize you may be new to FlightAware. If so, welcome aboard. If you have any other questions, please know that there is a search feature also available at the top of each forum page, along with a link to the questions/answers (FAQs) for FlightAware. Going through them will bring up a lot of interesting stuff.
Also feel free using the forum for questions if you can’t find your answer using search (sometimes you have to put in some really off-beat keywords and if you’re not familiar with aviation lingo, you may not be able to find what you want).
Oh, and congratulations on recognizing the South Dakota/North Dakota border on a map without labels! Unfortunately, a lot of people today cannot find their own state on a label-less map, much less find other states! 
(Disclaimer: This is a joke, not sarcasm!)
This is a known issue at the moment, although it is very annoying it is being worked on. I haven’t seen anything on any news program about a plane crash so I would imagine that your son is totally fine 
EDIT: Go to www.LiveATC.net and on the left side you will see something called “LiveATC Archives”, click it. Make sure you have Feb 24th selected and, on the drop down menu, look for “KSEA Tower - Seattle, WA”. Once you’ve done that select 2300Z-2330Z from the other drop down menu. It will automaticly open up in Windows Media Player. Once that happens, fast forward ahead to 14:55 and listen away to your son’s aircraft landing at KSEA!