I was a passenger aboard a Southwest flight between Omaha and Las Vegas on Wed (4/11) cruising at about 38,000 feet (based on the FlightAware tracker). Another commercial aircraft passed us directly in front of us from the 3 o’clock position. The vertical separation was probably only about 100 to 200 feet and within a couple of seconds of crossing each others flight paths. It was so close that I could see the passenger windows of the other plane very clearly.
In my opinion, this was way too close and appears to have been a controller error. Am I wrong? What is allowed?