Narrative:

While on taxiway a, abeam our gate, taxiway a was blocked by aircraft Y waiting for gate. Captain elected to take taxiway B2 to taxiway B to taxiway B1 to taxiway a. Ground control cleared us. As we maneuvered, we appeared to be right of centerline, but well within limits of taxiway. We later became aware that the #4 engine had come in contact with a taxiway sign. At no time throughout the maneuver did any of the crew feel a concern for engine clearance. The only area of concern was regarding being slightly right of centerline during rather tight maneuvering. I was aware that the wing was overhanging the island area, but I thought that we should have plenty of clearance vertically. Supplemental information from acn 548589: I was aware that I was making use of the entire width of the txwys to make the initial left turn followed by the 90 degree turn onto taxiway B, then to taxiway B1, where we re-entered taxiway a. My main effort was to ensure the aircraft stayed on the taxiway. A few mins later at taxiway echo, on taxiway a, we were told to return to gate for weight and balance problem. At gate, we were advised by mechanic that there were scrapes on bottom of engine #4 from contact with taxiway sign. At no time were any of us aware of this. I have made the same turns on taxi out 2 times before with no problems, but did note not much room. Other 2 times I was able to offset right before turn. This time could not since we were at taxiway B2 already. Callback conversation with reporter acn 548590 revealed the following information: an airport operations specialist revealed that strict adherence to taxiway ctrlines is required, especially in the area referred to in this report, if obstacle clearance is to be assured.

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Original NASA ASRS Text

Title: A B747-400 CREW, TAXIING FOR TKOF AT SFO, STRAYED FROM TXWY CTRLINE COMING INTO CONTACT WITH A TXWY SIGN.

Narrative: WHILE ON TXWY A, ABEAM OUR GATE, TXWY A WAS BLOCKED BY ACFT Y WAITING FOR GATE. CAPT ELECTED TO TAKE TXWY B2 TO TXWY B TO TXWY B1 TO TXWY A. GND CTL CLRED US. AS WE MANEUVERED, WE APPEARED TO BE R OF CTRLINE, BUT WELL WITHIN LIMITS OF TXWY. WE LATER BECAME AWARE THAT THE #4 ENG HAD COME IN CONTACT WITH A TXWY SIGN. AT NO TIME THROUGHOUT THE MANEUVER DID ANY OF THE CREW FEEL A CONCERN FOR ENG CLRNC. THE ONLY AREA OF CONCERN WAS REGARDING BEING SLIGHTLY R OF CTRLINE DURING RATHER TIGHT MANEUVERING. I WAS AWARE THAT THE WING WAS OVERHANGING THE ISLAND AREA, BUT I THOUGHT THAT WE SHOULD HAVE PLENTY OF CLRNC VERTLY. SUPPLEMENTAL INFO FROM ACN 548589: I WAS AWARE THAT I WAS MAKING USE OF THE ENTIRE WIDTH OF THE TXWYS TO MAKE THE INITIAL L TURN FOLLOWED BY THE 90 DEG TURN ONTO TXWY B, THEN TO TXWY B1, WHERE WE RE-ENTERED TXWY A. MY MAIN EFFORT WAS TO ENSURE THE ACFT STAYED ON THE TXWY. A FEW MINS LATER AT TXWY ECHO, ON TXWY A, WE WERE TOLD TO RETURN TO GATE FOR WT AND BAL PROB. AT GATE, WE WERE ADVISED BY MECH THAT THERE WERE SCRAPES ON BOTTOM OF ENG #4 FROM CONTACT WITH TXWY SIGN. AT NO TIME WERE ANY OF US AWARE OF THIS. I HAVE MADE THE SAME TURNS ON TAXI OUT 2 TIMES BEFORE WITH NO PROBS, BUT DID NOTE NOT MUCH ROOM. OTHER 2 TIMES I WAS ABLE TO OFFSET RIGHT BEFORE TURN. THIS TIME COULD NOT SINCE WE WERE AT TXWY B2 ALREADY. CALLBACK CONVERSATION WITH RPTR ACN 548590 REVEALED THE FOLLOWING INFO: AN ARPT OPS SPECIALIST REVEALED THAT STRICT ADHERENCE TO TXWY CTRLINES IS REQUIRED, ESPECIALLY IN THE AREA REFERRED TO IN THIS RPT, IF OBSTACLE CLRNC IS TO BE ASSURED.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.