AIR TAXI SMT ENTERS RWY WITH ANOTHER ACFT ON ROLL OUT.

Narrative

I INADVERTENTLY TAXIED ONTO A RWY AS ANOTHER SMT WAS 'ROLLING OUT' AFTER LNDG. PRIOR THERETO I HAD SEARCHED FOR OTHER ACFT IN THE PATTERN; HAD MADE 2 RADIO CALLS STATING MY INTENT TO 'TAXI BACK FOR TKOF.' I NEITHER SAW THE OTHER ACFT; NOR HEARD THE OTHER PLT'S POS RPTS (HE SAID HE MADE 3; AND I DO NOT DOUBT HE DID; BUT I DID NOT HEAR THEM). HE LANDED ON RWY 17; AND I TAXIED ONTO THE RWY FROM THE ACCESS APPROX 2/3 FROM THE APCH END. HE SHOUTED MY NAME AND THAT IS WHEN I SAW HIM (122.9). I MOVED TO THE W SIDE OF THE RWY AND APPLIED FULL PWR. HE HAD TO APPLY HVY BRAKING. WHAT COULD HAVE BEEN A SERIOUS ACCIDENT WAS NOT FURTHER MOMENTOUS. WE OPERATE TOURS TO THE GRAND CANYON. WE ARE ALL AWARE; AND STRIVE TO OPERATE SAFELY. BUT THIS TIME WE; OR I; NARROWLY AVERTED A COLLISION. I BELIEVE IT POSSIBLE MY RADIO'S VOLUME WAS TOO LOW; AND THERE ARE TIMES AND CIRCUMSTANCES WHEN; FROM THE RAMP AREA OF THIS AIRSTRIP; LNDG ACFT ARE ALMOST INVISIBLE AGAINST THE BACKDROP OF TERRAIN. STILL; I AM HAUNTED BY WHAT MIGHT HAVE BEEN. I HAVE RECOMMENDED WE ALL TAKE MORE TIME ON THE RAMP BEFORE TAXIING ONTO THE RWY; TO LOOK LONGER AND LISTEN UP; AND TO MAKE THE EXTRA CALL INQUIRING OF INBOUND TFC.