MAS is Malaysian Airline System....BUT, me thinks ( long shot ) that this particular aircraft is a Mexican originating flight and carrier.
There is a MASair in the "aero parts" page on the web.
Therefore, I suspect (especially as the aircraft was green ! The Mexican color) that it is Mexcan Air Services operating MEX or GUD to LAX Airport.
I also believe these DC8's were leased to them by Fast Air out of Miami.