ACR LGT EXPERIENCES RAMP EXCURSION DURING RAMP OP RAMP DEP PROC DURING PWRBACK OP.

Narrative

THE PWR BACK FROM GATE AT ICT WAS A NORMAL STRAIGHT PWR BACK TO ALL CREW INDICATIONS. WE WERE MOVING AT THE PACE OF A SLOW WALK; AND I WAS MONITORING THE SIGNALS OF THE FORWARD GUIDEMAN PLUS THRUST INDICATIONS AND OUR POS ON THE RAMP. I SAW NO PWR FORWARD SIGNALS FROM THE FORWARD GUIDEMAN UNTIL IT WAS TOO LATE. I DID SEE THE L WING WALKER WAVING 1 ARM FORWARD. BUT DID NOT KNOW WHAT HE WAS INDICATING SINCE HE GAVE NEITHER A STOP NOR A PWR FORWARD SIGNAL IN THE SECOND I HAD TO EVALUATE HIS ACTION. I RECEIVED THE FIRST INDICATION THAT ANYTHING WAS WRONG WHEN I HEARD A CRUNCHING SOUND AND FELT THE NOSE RISE. AT THAT POINT THE GUIDEMAN ON THE NOSE WAS GIVING A FORWARD SIGNAL; AND I IMMEDIATELY CAME OUT OF REVERSE AND APPLIED FORWARD THRUST. WITH THE ACFT STOPPED AND NO OTHER INDICATIONS FROM THE RAMP PERSONNEL; I SET THE PARKING BRAKE. WE WERE THEN INFORMED BY GND CTL THAT THE MAIN GEARS WERE OFF THE RAMP BY SEVERAL FT AND IN THE MUD. PORTABLE STAIRS WERE BROUGHT TO THE AIRPLANE; AND OUR 49 PAX DEPLANED WITHOUT INCIDENT. THE PLANE WAS TOWED BACK ONTO THE RAMP UNDER THE SUPERVISION OF AIRLINE'S ACFT RECOVERY TEAM. AFTER THEY INSPECTED THE ACFT AND DEEMED IT AIRWORTHY; WE FLEW THE ACFT TO DFW. IN ORDER TO PREVENT A RECURRENCE; THERE NEEDS TO BE BETTER STANDARDIZED PROCS FOR THE WING WALKERS TO SIGNAL THE FORWARD GUIDEMAN AND THE COCKPIT CREW THAT PWR BACK SHOULD CEASE. SUPPLEMENTAL INFO FROM ACN 233461: I ALSO BELIEVE THE GND REF USED BY THE GUIDEMAN TO DIRECT A 'COME FORWARD' SHOULD BE MORE PROMINENT. IT WAS DIFFICULT FOR ME TO SEE THE END OF THE YELLOW LINE HE USES AS A NOSEWHEEL REF; WHEN I STOOD IN HIS SPOT AFTER DEPLANING.