Narrative:

At sfo early morning before daylight. WX was low ceiling and visibility. Air carrier X sfo-lax we encountered the following chain of events: taxiing on outer to runway 01L we turned onto taxiway 'hotel' holding short of runway. We were cleared into position to hold. As we started to taxi into position on runway 01L we noticed the lights of an aircraft approaching from the right. This aircraft was taking off. We stopped our taxi and prevented a collision of our aircraft and the approaching aircraft. We were subsequently cleared into position again, and then cleared for takeoff. After arriving at lax we talked by telephone to sfo tower supervisor. We also talked to our flight mgrs at sfo and lax. We learned that sfo local procedure is to use taxiway 'microphone' to enter runway 01L for takeoff. There is no published procedure for using taxiway 'microphone' instead of 'hotel' to enter the runway. Also the tower supervisor said the tower cannot see the departure end of runway 01L in low visibility conditions. We also discussed the tower, ground surveillance radar and why the controller did not know that we were entering the runway at taxiway 'hotel'. The supervisor explained that their ground radar gives ambiguous returns and cannot be relied upon 100 percent. In conclusion the sfo tower should advise aircraft departing runway 01L that the runway entry point for takeoff is taxiway 'microphone' not taxiway 'hotel' which is at the end of the runway. In low visibility operations the same incident could be repeated to end in an accident.

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Original NASA ASRS Text

Title: ACR Y HAD LTSS FROM ACR X DURING TKOF ROLL. SYS ERROR.

Narrative: AT SFO EARLY MORNING BEFORE DAYLIGHT. WX WAS LOW CEILING AND VISIBILITY. ACR X SFO-LAX WE ENCOUNTERED THE FOLLOWING CHAIN OF EVENTS: TAXIING ON OUTER TO RWY 01L WE TURNED ONTO TAXIWAY 'HOTEL' HOLDING SHORT OF RWY. WE WERE CLRED INTO POS TO HOLD. AS WE STARTED TO TAXI INTO POS ON RWY 01L WE NOTICED THE LIGHTS OF AN ACFT APCHING FROM THE R. THIS ACFT WAS TAKING OFF. WE STOPPED OUR TAXI AND PREVENTED A COLLISION OF OUR ACFT AND THE APCHING ACFT. WE WERE SUBSEQUENTLY CLRED INTO POS AGAIN, AND THEN CLRED FOR TKOF. AFTER ARRIVING AT LAX WE TALKED BY TELEPHONE TO SFO TWR SUPVR. WE ALSO TALKED TO OUR FLT MGRS AT SFO AND LAX. WE LEARNED THAT SFO LCL PROC IS TO USE TAXIWAY 'MIKE' TO ENTER RWY 01L FOR TKOF. THERE IS NO PUBLISHED PROC FOR USING TAXIWAY 'MIKE' INSTEAD OF 'HOTEL' TO ENTER THE RWY. ALSO THE TWR SUPVR SAID THE TWR CANNOT SEE THE DEP END OF RWY 01L IN LOW VISIBILITY CONDITIONS. WE ALSO DISCUSSED THE TWR, GND SURVEILLANCE RADAR AND WHY THE CTLR DID NOT KNOW THAT WE WERE ENTERING THE RWY AT TAXIWAY 'HOTEL'. THE SUPVR EXPLAINED THAT THEIR GND RADAR GIVES AMBIGUOUS RETURNS AND CANNOT BE RELIED UPON 100 PERCENT. IN CONCLUSION THE SFO TWR SHOULD ADVISE ACFT DEPARTING RWY 01L THAT THE RWY ENTRY POINT FOR TKOF IS TAXIWAY 'MIKE' NOT TAXIWAY 'HOTEL' WHICH IS AT THE END OF THE RWY. IN LOW VISIBILITY OPS THE SAME INCIDENT COULD BE REPEATED TO END IN AN ACCIDENT.

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.