A B-727-400 WINGLET STRUCK DURING PUSHBACK BY ANOTHER B- 727-400 TAXIING BY.

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I WAS IN FIRST OBSERVER SEAT DURING PUSHBACK FROM GATE; GETTING THE PAX COUNT FROM THE FLT ATTENDANT VIA THE INTERCOM. THE ACFT STOPPED AND THEN BEGAN MOVING FORWARD; RETURNING TO THE GATE (STILL UNDER TOW). OUR WINGWALKER ON THE GND TOLD OUR PUSHBACK MECH THAT ACR Y AIRLINES 747-400 HAD CLIPPED OUR WINGLET WITH HIS WINGLET AS HE TAXIED BY. WE RETURNED TO THE GATE AND THEY FOUND ONLY A SMALL 4 INCH CUT IN THE WINGLET; WHICH THEY RPTED AND SENT US ON OUR WAY AGAIN IN ABOUT 20 MINS. CAPT AND FLYING FO STATED THAT WE HAD BEEN CLRED TO PUSH AFTER ACR Z TAXIED BY. WE BEGAN PUSHBACK AFTER AN ACR Z PASSED BUT GND CTL THEN SAID; 'NOT THAT ACR Z; THE ACR Z 727.' AT THAT POINT THEY INSTRUCTED THE TUG DRIVER TO PULL BACK INTO THE GATE. GND CTL TOLD ACR Y AIRLINES; 'CAUTION FOR THE 747 PUSHED OUT OF GATE XA.' HE REPLIED SOMETHING TO THE EFFECT OF; 'WE ALWAYS EXERCISE CAUTION' JUST BEFORE HE CLIPPED US. OUR WINGWALKER COULD SEE IT COMING AND WAVED FRANTICALLY AT THE ACR Y AIRLINES PLANE; BUT WITH NO SUCCESS. ACR Y CONTINUED TO THE RWY APPARENTLY UNAWARE OF THE CONTACT UNTIL THE TWR TOLD HIM.