Date: 201912
Location: SFO.Airport, CA
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Flight phase: Taxi
ATC / advisory: Ground SFO
Reporter organization: Air Carrier
Reporter function: Lead Technician
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Human factors: Confusion; Communication Breakdown
Anomaly: Deviation / Discrepancy - Procedural Clearance; Ground Incursion Taxiway
Detector: Person Maintenance
When detected: Taxi
Result: Air Traffic Control Provided Assistance; Flight Crew Became Reoriented
Contributing factors: Airport; Human Factors; Procedure
Primary problem: Ambiguous

Narrative: I was assigned to taxi Aircraft X to Gate XX. After engine starts and briefing we proceeded to get clearance from the tower to taxi to the gate. We were told to proceed via 'Charlie 1; hold short 28R' which is really '10L' from our end. We held short for a while and while there we noticed Zulu was closed and there were vehicles and personnel moving cones and picking up cones nearby to our right. We were then told to 'cross 28R (again recognized; perceived; being it is 10L from our end); Sierra 3; Sierra 2; Zulu; hold short Bravo 1.' As we were about to proceed from Charlie 1 towards Sierra 3 it became apparently confusing. The only sign in view from our position on Charlie 1 was a physical standing sign for Sierra 4. Sierra 4 was most evident and the closure; personnel and vehicles on Zulu off to our right made it seem as if we shouldn't; wouldn't be given instructions towards that direction. We did not and could not find signage for Sierra 3. I proceeded to what I believed to be the correct and safest direction towards what would be Sierra 3. There is NO taxi line that takes you from Charlie 1 to Sierra 3. With the Sierra 4 sign off to the right from our position on Charlie 1 it is far to easy to assume Sierra 3 to the left. I realize the mistake in assuming; but the signage in that area along with the closure was not of help. The Sierra 3 and Sierra 2 signs are painted markings on the ground that are visible only when upon them. We got to Zulu short of Bravo 1 and were told by the ATC to call the tower when we got to the gate for a 'possible deviation.' I was going over what I may have done wrong but could not figure it out. I called the tower but they were busy; and the controller asked I call later. When we got back to the maintenance area and looked at the SFO Airport map I realized that I had not followed the correct path of travel. It appears that I went Charlie 1 to Sierra 4 which again was the taxi line in route with Charlie 1 to Sierra; Zulu; hold short Bravo 1. Even upon the map review I believe I was thrown off due to the closure; safety of the personnel; no evident signage for Sierra 3; Sierra 2 and no taxi line from Charlie 1 to Sierra 3.My training and situational awareness not only was in controlling a multi-million dollar aircraft; watching our parameters and indications but also in considering the safety of the personnel that were on Zulu extremely close to Sierra 2. We were taxiing under aircraft power and the turn from Sierra 2 to Zulu would have put them in the jet blast zone. My partner in the right hand seat is very thorough; conscientious and experienced; he repeated instructions perfectly and although clear from the air traffic controller; there was confusion with the aircraft under tow behind us and the aircraft behind them with the same instructions given to them. At that point the Controller got frustrated; made a statement to us all in that area to 'listen to the instructions!' and then asked Airfield Ops 'when Zulu would be open?' to which they replied 'about 5 minutes.'This area has been an issue in the past. We have had other movement individuals get in trouble here; day shift move teams; two of our present safety reps as well as night shift individuals of which Airfield Ops is aware as they have offered help in the past. We should have asked for 'progressive' or more explicit help in this hazardous area and maybe it should have been offered to us as this is a known area to be a problem. We should not have to be afraid of asking ATC for fear of being scolded or treated rudely. Although I feel that was not so much the case on this particular day; it certainly is much too often. It is difficult to understand; see or know all our perspective jobs and insights thereof.I am truly very sorry and apologize to all over this incident. It is a terrible feeling as I have been doing this job and moving aircraft for many years without incident. I respectfully ask for the air traffic controller and someone from Airfield Operations to please accompany us on a 'ride along' via the same route to see what we see from our end. I do believe it would help us all going forward taking the events of this incident in review and with ATC help we can come up with better training for our movement personnel. I have an idea for a training module or maybe just some literature for emphasis on movement in that area and hope to be; would like to be part of a positive solution to this area of the airfield.




Synopsis: Technician reported that while taxiing an aircraft from a maintenance area; the instructions issued by ATC were confusing and some of the taxiway markings and signage were non-existent or difficult to locate at SFO airport.