It seems that Oman Air is not tracked. I tried to to follow some of their aircrafts.
A4O-DC / A4O-DE
I only get:
"FlightAware couldn’t find flight tracking data for A4O-DC just yet.
Please double-check the flight number/identifier. If you typed it in correctly and it’s still not showing up, or you’re not completely sure of the flight number, you should use the FlightAware Flight Finder. If you know the origin and destination of the flight, it will help you find the proper flight number/identifier. "*
Looking around I found a note that Muscat Airport is in the secondary servicearea of flightaware and therefore tracking of MCT might be incomplete (flightaware.com/about/faq#intl). I assume Oman Air is also in the secondary area as it is based at MCT.