MLG HAS TCASII RA ON DSCNT; PROBABLY FALSE.

Narrative

ENRTE TO PDX WE WERE CLRED TO PDX VIA MOXEE 3 ARR TO CROSS FLOWR INTXN AT 10000 FT; 250 KIAS. DSNDING THROUGH 13000 FT; THE TCASII SUDDENLY ADVISED OF AN RA. I IMMEDIATELY LEVELED AT 12800 FT AND FOLLOWED THE TCASII MONITOR VERT SPD COMMANDS BACK UP TO 13000 FT. THE FO CALLED CTR ASKING IF WE HAD TFC AT 12 O'CLOCK. THE CTR TOLD US WE HAD BEEN SWITCHED TO APCH A FEW MI BACK (A CALL WE HAD NOT RESPONDED TO) AND TO SWITCH TO 118.1. WHILE SWITCHING TO 118.1 THE TCASII TFC DISAPPEARED. WE CHKED IN WITH PDX APCH CTL RPTING 13000 FT FOR 10000 FT. APCH CTL GAVE US A HDG AND LOWER ALT. THE CTR FREQ WAS BUSY AND IT WAS HARD TO GET A WORD IN TO ADVISE OF THE RA WHEN IT HAPPENED. THE TCASII TFC SHOWED BTWN 400 FT AND 500 FT BELOW US AT 12 O'CLOCK. WE WERE IN VFR CONDITIONS AT THE TIME AND BOTH LOOKING OUT TO GET VISUAL CONTACT. NO VISUAL CONTACT WAS MADE LEADING ME TO BELIEVE THIS WAS A FALSE RA BECAUSE OF THE SUDDEN APPEARANCE AND DISAPPEARANCE OF THE TFC ON THE TCASII SCREEN. THERE WAS NO MENTION OF ANY CONFLICTING AIR TFC BY ATC OR ANY MENTION OF THE RA AND LEVELOFF AT 13000 FT BY US BECAUSE AIR TFC CTL WAS BUSY.