A TUG TOWING A DC10 FROM A GATE TO THE MAINT HANGAR HAD A RWY INCURSION DUE TO RADIO COM PROBS WITH THE TWR. THE TUG'S RADIO WAS NOT WORKING; SO THE 'BRAKE RIDER' IN THE ACFT WAS RELAYING THE INSTRUCTIONS TO THE TUG DRIVER. THE 'BRAKE RIDER' APPARENTLY GOT CONFUSED BY SEVERAL AMENDMENTS TO THE TOWING INSTRUCTIONS AND THE TUG AND ACFT GOT ONTO A RWY THAT THEY WERE TO HOLD SHORT OF. ONE RPTR ALLEGES TRAINING TAKING PLACE IN THE TWR.

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ON JAN/THU/97; AT APPROX XA15 AM; MYSELF AND ANOTHER MECH WERE SENT TO TOW A DC10 FROM GATE XX TO THE MAINT BASE AT ZZZ. AFTER AN UNEVENTFUL PUSHBACK TO TXWY A; WE PROCEEDED ON TXWY A TO TXWY U HOLDING SHORT OF RWY 28L. (I WAS THE TUG DRIVER AND IN CONTACT WITH THE COCKPIT DUE TO THE FACT THAT THE RADIO IN THE TUG WAS TAGGED BROKEN. THE BRAKE RIDER WAS IN CONTACT WITH THE TWR.) THE BRAKE RIDER MADE A COMMENT THAT THE TWR WAS BUSY AND THEY WERE AMENDING THE DIRECTIONS SEVERAL TIMES. THE BRAKE RIDER SAID THE TWR HAD GIVEN HIM SEVERAL OPTIONS INCLUDING TXWY U TO TXWY R TO TXWY C; BUT WE WOULD HOLD STILL UNTIL FURTHER INSTRUCTION. THE BRAKE RIDER THEN SAID WE WERE CLR TO CROSS RWY 28L. WE STARTED TO CROSS WHEN THE BRAKE RIDER SAID THE TWR TOLD HIM WE INCURRED THE RWY. THE BRAKE RIDER SAID HE BELIEVED WE WERE CLR TO CROSS RWY 28L. WE STOPPED ON TXWY U AT RWY 28R. AFTER SEVERAL MINS; THE BRAKE RIDER TOLD ME WE WERE CLR TO CROSS RWY 28R. WE WENT ABOUT 20 YARDS AND WE WERE TOLD TO STOP. WE CAME TO A STOP; STILL SHORT OF RWY 28R. AFTER SEVERAL MINUTES WE WERE GIVEN CLEARENCE TO CROSS RWY 28R. DUE TO THE TWR TRAINING AND WX CONDITIONS; A RWY INCURSION DID OCCUR. THE DIRECTIONS WERE AMENDED NUMEROUS TIMES. SUPPLEMENTAL INFO FROM ACN 356950: I WAS RIDING BRAKES AND OPERATING THE RADIO; TALKING AND BEING DIRECTED BY ZZZ GND CTL. THE EVENTS STARTED WITH MY PARTNER AND I AT GATE XX READY TO PUSH BACK. I CALLED ZZZ GND CTL FOR CLRNC TO PUSH BACK. 2 OTHER AMENDMENTS TO THE ORIGINAL INSTRUCTIONS WERE MADE BY GND. AS RADIO OPERATOR I WAS CONFUSED BY THE CHANGES MADE. I ASKED GND TO REPEAT THEIR INSTRUCTIONS AND TOLD THEM THAT I WAS HAVING HARD TIME UNDERSTANDING THEIR INSTRUCTIONS. GND REPEATED BY SAYING; TUG XX GO TO TXWY U; HOLD SHORT RWY 28L; TAKE TXWYS U; R; AND C. HALFWAY ACROSS THE RWY 28L; GND CALLED AND SAID; TUG XX STOP! I TOLD GND CTL THAT WE WERE HALFWAY ACROSS. AT THAT POINT ANOTHER CTLR TOOK OVER. TUG XX HOLD SHORT OF RWY 28R; ON TXWY U; READBACK. WE WERE IN POS OF THE FIRST HOLD LINE ON TXWY U AND MOVING TOWARDS RWY 28R. GND CTL CALLED AND SAID TUG HOLD SHORT OF RWY 28R. READ BACK; WE STOPPED 20 YARDS BEFORE RWY 28R THRESHOLD; ON TXWY U. THEN WE WERE CLRED TO CROSS RWY 28R TO TXWY Q AND TO W GATE. THE RWY INCURSION TOOK PLACE ON TXWY U XING RWY 28L.