UNAUTH UNCOORD TAXI; PREMATURE ACFT MOVEMENT DURING RAMP OP RAMP DEP PUSHBACK PROC.

Narrative

AFTER PUSHBACK AND ENG START; I CLRED THE GND CREW OF INTERPHONE. DUE TO OUR LOCATION; THE PUSH CREW CLRS OFF TO THE R OF THE ACFT. I LOOKED TO THE R AND THE FO LOOKED OUT HIS WINDOW AND SAID 'CLR R' I LOOKED OUT TO THE L AND FORWARD OF ACFT AND SAW IT WAS CLR SO I TURNED ON THE TAXI LIGHTS AND RELEASED THE BRAKES. ALMOST IMMEDIATELY I FELT THE ACFT COME INTO CONTACT WITH SOMETHING AND RESET THE BRAKES. WHEN THE GROUND CREW CAME BACK INTO INTERPHONE CONTACT; I WAS INFORMED THAT THE TUG HAD NOT BEEN CLR BUT HAD BEEN CONCEALED FROM OUR SIGHT UNDER THE ACFT. APPARENTLY I HAD COME INTO CONTACT WITH THE TOWBAR. AFTER INSPECTING FOR DAMAGE TO THE ACFT; MAINT INFORMED ME THAT THERE WAS NONE. I ONCE AGAIN CLRED HIM OFF HEADSET AND VISUALLY SAW THAT THE TUG WAS CLR. I RESUMED TAXI AND THE FLT CONTINUED WITHOUT FURTHER INCIDENT. A CONTRIBUTING FACTOR IN THIS INCIDENT IS A DIFFERENCE IN PROCS BTWN MY COMPANY AND THE AIRLINE THAT HANDLES US IN SEA. WE NORMALLY HAVE 2 OR MORE GND CREWMEMBERS DURING PUSHBACK. 1 OF WHOM REMAINS IN VISUAL CONTACT UNTIL ALL EQUIP IS REMOVED AND WE ARE CLRED TO TAXI. UNBEKNOWNST TO ME THE AIRLINE DOING THIS PUSHBACK HAS 1 PERSON DOING THE ENTIRE PROC. WHEN HE CLRED OFF INTERPHONE AND DISAPPEARED FROM VIEW; I TOOK IT TO MEAN THAT WE WERE CLRED TO TAXI.