A B-777 BEING TAXIED TO THE HANGER MADE A RWY INCURSION DUE TO A READBACK ERROR BY THE TAXI TECHNICIAN AND A FAILURE TO CHALLENGE BY THE CTLR.

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THIS IS A DESCRIPTION OF EVENTS OF A POSSIBLE RWY INCURSION THAT TOOK PLACE ON OCT/SAT/2001 AT ORD INTL ARPT. MYSELF AND ANOTHER MECHANIC HAD BEEN GIVEN THE ASSIGNMENT TO MOVE ACFT FROM THE INTL TERMINAL TO THE HANGER CENTER OF ACR X AIRLINES. THE TIME OF DAY WAS APPROX XA00 HRS; THE WX WAS SEVERE THUNDER STORMS; HEAVY RAINS AND WIND. WE HAD BEEN CLRED TO THE W PORT OF THE INTL RAMP BY RAMP CTL AND INSTRUCTED TO CONTACT GND CTL FOR TAXI INSTRUCTIONS. AFTER STOPPING AT THE DELTA 2 INTXN WE CONTACTED GND USING THE 'N' NUMBER OF THE ACFT. GND CHANGED OUR CALL SIGN TO ACR X AND WE WERE GIVEN THE INSTRUCTION TO TAKE ALPHA 18; ALPHA; TO ALPHA 6; JULIET; WHISKEY; TANGO; YANKEE. WE PROCEEDED AROUND THE TERMINAL AND AS WE APCHED ALPHA 8 WE NOTICED A LONG LINE OF ACFT ON THE TANGO TXWY BLOCKING SEVERAL ACFT ON THE JULIET TXWY. I TOLD MY PARTNER THAT I THOUGHT WE MIGHT BE IN FOR A LONG WAIT AND HE SUGGESTED THAT WE CONTACT GND TO SEE IF WE COULD GET ANOTHER RTE; I SAID YES. SO MY PARTNER CALLED GND AND INFORMED OF THE LINE AND GND CTL TOLD US TO HOLD SHORT OF ALPHA 6 AND HE WOULD SEE WHAT HE COULD DO. WE DID THIS AND AFTER A SHORT TIME THE CTLR CAME BACK WITH INSTRUCTIONS TO PROCEED ON ALPHA TO ECHO; TURN ON ECHO AND HOLD SHORT OF RWY 22R. WE PROCEEDED ON TO ECHO AND AS WE APCHED ECHO THE CTLR CAME BACK AND SAID; TURN LEFT ON ECHO CLR TO CROSS 22R; ECHO; YANKEE. THIS IS WHAT I HEARD AND AT THE TIME WAS COMPLETELY CONFIDENT OF THAT. MY PARTNER THEN REPEATED THE INSTRUCTIONS BACK AND THE TWR HAD NO RESPONSE. SUBSEQUENTLY AFTER HEARING THE TWR TAPES IT IS APPARENT THAT THE TWR COM AND WHAT I THOUGHT WAS SAID WERE NOT THE SAME. AND THAT'S WHAT MY PARTNER REPEATED BACK WAS NOT THE SAME INSTRUCTIONS AND NOT WHAT I THOUGHT WAS SAID. THE TWR'S INSTRUCTIONS WERE TO TAKE ECHO CLR TO CROSS 22R LEFT ON HOTEL; TANGO. THE TWR'S INSTRUCTIONS LEFT OUT THE FINAL TXWY OF YANKEE. ALSO IT WAS DISCOVERED THAT MY PARTNERS READ BACK WAS LEFT ON ECHO CLR TO CROSS 22R; HOTEL; YANKEE. THIS WAS NOT THE TWR'S ORIGINAL INSTRUCTIONS AS HE SAID THEM; YET WHEN REPEATED BACK INCORRECTLY THEY WENT UNCHALLENGED. SUBSEQUENTLY WE PROCEEDED ON ECHO; WE APCHED 22R LOOKED IN BOTH DIRECTIONS AND SAW NO TFC EITHER WAY; CROSSED 22R; CONTINUED ON ECHO AND ENDED UP INTERSECTING RWY 27R. AT THIS TIME WE HEARD LITTLE RADIO COM AND BELIEVED THERE TO BE A GND STOP IN AFFECT DUE TO THE SEVERE WX IN THE AREA. AS WE APCHED THE RWY 27R AND CROSSED THE HOLD LINES MY PARTNER QUESTIONED WHY ANOTHER ACFT WAS ON THE RWY AT THE SAME TIME THAT WE WERE. I LOOKED IN THE DIRECTION AND SAW AN ACFT ON FINAL ROLL OUT TURNING ONTO A TURNOFF. I SAID TO HIM THAT I THOUGHT THAT THE ACFT WAS MUCH FARTHER DOWN FIELD; AND WAS TURNING OFF. IT WAS POSSIBLE THAT A MISJUDGMENT IN TIMING HAD OCCURRED OR THAT THE OTHER ACFT HAD ROLLED OUT LONGER THAN WAS EXPECTED AND WENT TO ANOTHER TURN OFF. THAT WAS WHY WE HAD ENDED UP ON THE RWY AT THE SAME TIME. WE CROSSED 27R AND ON THE OTHER SIDE THE TWR THEN CALLED AND SAID ACR X YOU WERE NOT CLRED TO CROSS 27R. MY PARTNER RESPONDED THAT HE HAD NOT TOLD US TO HOLD SHORT OR WE WOULD HAVE DONE SO. THERE WAS A LENGTHY PAUSE AND THE TWR RESPONDED WITH THAT HE HAD TOLD US TO TURN ON HOTEL. MY PARTNER THEN SAID THAT HE HAD READ BACK THE INSTRUCTIONS THAT THE CTLR HAD GIVEN HIM. HE THEN REPEATED THEM AGAIN; TURN ON ECHO CLR TO CROSS 22R; HOTEL; YANKEE. AT THIS POINT I'M THINKING THAT THIS IS THE FIRST TIME I HEARD THE HOTEL INSTRUCTION. THE CTLR THEN RESPONDED WITH; HOTEL DOESN'T INTERSECT WITH YANKEE. WE WAITED FOR A SHORT TIME AND HEARD THE CTLR TALKING TO OTHER ACFT AND PROCEED TO THE HANGER CENTER USING ECHO TO YANKEE. THERE ARE THE EVENTS AS TO THE BEST OF MY RECOLLECTION. SUBSEQUENTLY HEARING THE TWR TAPES; AS I HAVE MENTIONED EARLIER; REVEALED THE TWR'S COM TO BE DIFFERENT FROM WHAT I UNDERSTOOD. HOW THIS OCCURRED; I CAN ONLY SPECULATE. THE WX PLAYED SOME ROLL. HEAVY RAINS AND WINDS ALONG WITH THE NECESSARY USE OF THE WINDSHIELD WIPERS CAUSED AN INCREASE IN NOISE PLUS POOR VISIBILITY. THE TAPES ONLY REVEAL WHAT WAS TRANSMITTED AND RECEIVED BY THE TWR. IF SOMEONE ELSE HAPPENED TO KEY A MICROPHONE DURING THAT XMISSION IT WOULD BE BLOCKED OR AT LEAST DIFFICULT TO HEAR BY THE ACFT. FAMILIARITY WITH COMMONLY USE ROUTES AND MIND SETS FACTOR INTO THIS. INCONSISTENCY WITH PROCS ALSO CAME INTO THIS. IT IS COMMON PROC FOR GND CTL TO TELL A TAXIING ACFT APCHING AND INTERSECTING AN ACTIVE RWY TO HOLD SHORT AND SWITCH TO TWR CTL FREQ FOR CLRNC TO CROSS THE RWY. IN THIS INSTANCE THIS WAS NOT DONE AND GND CTL COMMUNICATED THE CLEARANCES SOLELY. PLUS BOTH PARTIES DECISION TO ASSUME MISUNDERSTOOD AND OR INCORRECT XMISSIONS; AND TO LET THEM GO UNCHALLENGED FACTOR IN AS WELL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE TAXI INSTRUCTIONS GIVEN WERE NOT THE NORMAL RTE TO THE HANGER BUT THIS DAY WAS NOT NORMAL AS HEAVY THUNDERSTORM WERE STOPPING TFC. THE RPTR SAID THE GND CTLR GAVE THE FOLLOWING INSTRUCTIONS 'TAKE ECHO CLR TO CROSS 22R LEFT ON HOTEL; TANGO' AS VERIFIED BY THE TAPES. THE READBACK FROM THE TAXI TECHNICIAN WAS 'LEFT ON ECHO CLR TO CROSS 22R; HOTEL YANKEE.' THE RPTR STATED THIS WAS WRONG AND WENT UNCHALLENGED ALSO VERIFIED BY THE TAPES. THE RPTR STATED THE USUAL PROCS WERE NOT USED ON THIS DAY. THE RPTR SAID IT IS COMMON PROC FOR THE GND CTLR TO TELL A TAXIING ACFT APCHING AND INTERSECTING AN ACTIVE RWY TO HOLD SHORT AND SWITCH TO TWR FREQ FOR CLRNC TO CROSS THE RWY. THE RPTR STATED THIS WAS NOT DONE. CALLBACK FROM ACN 527513: THE RPTR STATED THE RWY INCURSION WAS CAUSED MAINLY AN ERROR ON THE TAXI CREW IN THE READBACK WHICH WENT UNCHALLENGED BY THE GND CTLR. THE RPTR SAID ALL OF THE NORMAL PROCS WERE NOT IN EFFECT ON THAT DAY; HEAVY THUNDERSTORMS; COCKPIT NOISE WITH WINDSHIELD WIPERS ON FULL; GARBLED AND UNCLR COMS ALL CONTRIBUTED TO THIS ERROR.