PWRBACK OFF RAMP.

Narrative

DURING PWRBACK; BOTH ACFT MAIN GEAR LEFT THE HARD SURFACE OF THE RAMP AREA. THE PWRBACK APPEARED NORMAL UNTIL THE COORDINATOR GAVE THE COME AHEAD SIGNAL. ALMOST SIMULTANEOUSLY WITH MOVING THE THRUST LEVERS TO THE FORWARD THRUST POS; THE ACFT BACKED OFF THE HARD SURFACE. THE ENGS WERE SUBSEQUENTLY SHUT DOWN AND THE PAX DEPLANED THROUGH THE MAIN CABIN DOOR USING PORTABLE STAIRS. THE ACFT WAS THEN TOWED BACK TO THE GATE WHERE A MAINT INSPECTION REVEALED NO STRUCTURAL DAMAGE. THE RAMP IS UNLIGHTED AND THIS WAS A NIGHT PWRBACK. THE RAMP WAS ALSO DRY; AND THE ONLY RESTR TO VISIBILITY WAS THE DARKNESS. A SHORT PWRBACK WAS ALL THAT WAS NECESSARY; BUT THE COORDINATOR CONTINUED TO PWR US BACK; PROBABLY TO MAKE THE TURN OUT EASIER FOR US. AS IT WAS A TURNING PWRBACK; THE COORDINATOR MAY NOT HAVE ANTICIPATED A PROB WITH THE BACK OF THE RAMP. EVEN AFTER THE MAIN GEAR LEFT THE RAMP; IT DID NOT APPEAR THAT THE COORDINATOR WAS AWARE OF A PROB AS HE CONTINUED TO GIVE US THE 'COME STRAIGHT AHEAD' SIGNAL. IF THE WING WALKER MADE ANY ATTEMPT TO STOP THE PWRBACK; I DID NOT NOTICE IT AS I WAS FULLY CONCENTRATING ON THE COORDINATOR'S SIGNALS.