A DSNDING C172 HAS AN NMAC WITH A XING GA ACFT AT 10000 FT 18 NM N OF PRC; AZ.

Narrative

WE WERE IFR FROM GRAND CANYON (GCN) TO PRESCOTT; AZ (PRC). I WAS SITTING IN THE R FRONT SEAT; WHILE THE PIC WAS IN THE FRONT L SEAT. PIC WAS FLYING; I WAS WORKING THE RADIOS. WHEN ZAB HANDED US OFF TO PRC TWR; HE ADVISED US THAT A PART 121 FLT WAS INBOUND FROM THE S TO LAND AT PRC (IT IS COMMON PRACTICE AT PRC FOR GA ACFT TO CANCEL IFR WHEN APCHING IN VMC BECAUSE PRC TWR IS ONLY ALLOWED TO HANDLE 1 IFR ACFT AT A TIME). ON INITIAL CALL-UP TO TWR; I STATED THE USUAL ATIS; POS; AND INTENTIONS (TO DO A PRACTICE HOLD AT DRK VOR AS PUBLISHED; THEN LAND AT PRC). I ALSO CANCELED IFR ON INITIAL CALL-UP. TWR ADVISED US TO CHANGE OUR SQUAWK CODE; AND RPT ENTERING THE HOLD. THE DSCNT CHKLIST HAD BEEN COMPLETED; WHICH MEANS BEACON AND LNDG LIGHTS WERE ON. AS WE DSNDED THROUGH 10000 FT; THE PIC AND I BOTH SAW THE MOONEY AT THE SAME TIME AT OUR 2 O'CLOCK POS OF ABOUT 1000 FT HORIZLY AND 50 FT VERTLY (WE WERE ABOVE THE MOONEY). WE PASSED FROM HIS L TO R; 500 FT IN FRONT OF AND STILL 50 FT HIGHER. ABOUT 30 SECONDS AFTER THE NMAC; I CALLED PRC TWR AND ASKED IF THEY WERE TALKING TO A MOONEY IN THE PAULDEN AREA; THEY ADVISED THEY WERE NOT. THE PIC DECIDED NOT TO CONTINUE WITH THE HOLD AND WE LANDED WITHOUT FURTHER INCIDENT.