Narrative:

The first officer was doing a visibility approach to 28L at sfo. At about 1200' AGL with gear down and flaps 30 degrees, we did the final descent checklist and noticed 'a' system hydraulic quantity was 0, followed a few seconds later with a loss of 'a' system pressure. We were now approaching 500' AGL and elected to continued for landing with flaps 30 degrees (we had planned to use 25 degrees because of our weight, but had gone to 30 degrees earlier to slow down and lose altitude). We advised the sfo tower we had lost a hydraulic system and probably wouldn't be able to clear runway after landing as we wouldn't have nose wheel steering. We requested emergency equipment standing by. With the aid of a jump seat pilot, we quickly went through the checklist for loss of 'a' hydraulics, noting in particular that we would have no nose wheel steering after landing. The first officer was doing great, so let her land, which was on the center approximately 1500' down the runway. After landing the reversers appeared to work normally, but because we were rolling down the runway quickly (maximum gross weight for landing and no ground spoilers because of loss of hydraulics), I started getting on the brakes with the first officer. Initially braking seemed normal, but as we slowed to near 70 KTS the aircraft starting veering to the right. I assumed control at this point and tried to keep the aircraft going straight with hard left braking. But at this point the braking didn't appear to be responding and we continued toward the right of the runway and went off it at about 30 KTS. The ground was soft from a recent rain, so we sank into the ground fairly quickly and stopped. I did the emergency evacuate/evacuation shutdown check while the first officer was communicating with the tower and the passenger. I sent the jump seat pilot back to the cabin for an assessment of our condition. He quickly reported back that everything appeared ok. We also got a report from the tower that everything looked ok and the emergency equipment personnel who had already arrived indicated no serious problem, so I decided not to do an emergency evacuate/evacuation and had the passenger stay seated. Later we opened the cabin doors and extended the slides so people could get off the aircraft. But as we started to get people off, I got a request from 1 of the emergency personnel below not to use the slides as a ramp was on the way. We stopped exiting people via the slides after 13 people (out of 116 aboard) had gotten off. The rest of the people exited via the ramp stand brought to the main entrance. There were no apparent injuries and only minor damage to the aircraft. This incident was caused by a mechanical problem (loss of hydraulics) and I feel everything went as planned and expected, with the exception that I was surprised to find out, even though we were very aware we didn't have nose wheel steering, that we couldn't control the aircraft with the use of brakes, etc as we slowed. I have practiced this type of problem many times during training and had not expected to lose complete directional control before we stopped. It may be explained by the fact that it appears that we may have lost all braking near the end of the roll. As we exited the runway it was apparent that we were going to strike a runway equipment box, which was a VASI box. It looked like it could have caused some damage, but it was not anchored too securely (hopefully by design) and it apparently did minimal damage as it broke away. Supplemental information from acn 169528: there was some initial confusion between information given re: the egress of the passenger. Egress seemed orderly, even with the slight confusion re: the back slides. The slide on door 1L jammed, apparently, and did not deploy.

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Original NASA ASRS Text

Title: ACR MLG LOST 'A' SYSTEM HYDRAULIC QUANTITY AND PRESSURE ON FINAL FOR RWY 28L AT SFO. NOSE WHEEL STEERING WAS LOST AND THE ACFT EXITED THE RWY DURING ROLLOUT WITH MINOR ACFT DAMAGE.

Narrative: THE F/O WAS DOING A VIS APCH TO 28L AT SFO. AT ABOUT 1200' AGL WITH GEAR DOWN AND FLAPS 30 DEGS, WE DID THE FINAL DSNT CHKLIST AND NOTICED 'A' SYS HYD QUANTITY WAS 0, FOLLOWED A FEW SECS LATER WITH A LOSS OF 'A' SYS PRESSURE. WE WERE NOW APCHING 500' AGL AND ELECTED TO CONTINUED FOR LNDG WITH FLAPS 30 DEGS (WE HAD PLANNED TO USE 25 DEGS BECAUSE OF OUR WT, BUT HAD GONE TO 30 DEGS EARLIER TO SLOW DOWN AND LOSE ALT). WE ADVISED THE SFO TWR WE HAD LOST A HYD SYS AND PROBABLY WOULDN'T BE ABLE TO CLR RWY AFTER LNDG AS WE WOULDN'T HAVE NOSE WHEEL STEERING. WE REQUESTED EMER EQUIP STANDING BY. WITH THE AID OF A JUMP SEAT PLT, WE QUICKLY WENT THROUGH THE CHKLIST FOR LOSS OF 'A' HYDS, NOTING IN PARTICULAR THAT WE WOULD HAVE NO NOSE WHEEL STEERING AFTER LNDG. THE F/O WAS DOING GREAT, SO LET HER LAND, WHICH WAS ON THE CENTER APPROX 1500' DOWN THE RWY. AFTER LNDG THE REVERSERS APPEARED TO WORK NORMALLY, BUT BECAUSE WE WERE ROLLING DOWN THE RWY QUICKLY (MAX GROSS WT FOR LNDG AND NO GND SPOILERS BECAUSE OF LOSS OF HYDS), I STARTED GETTING ON THE BRAKES WITH THE F/O. INITIALLY BRAKING SEEMED NORMAL, BUT AS WE SLOWED TO NEAR 70 KTS THE ACFT STARTING VEERING TO THE RIGHT. I ASSUMED CTL AT THIS POINT AND TRIED TO KEEP THE ACFT GOING STRAIGHT WITH HARD LEFT BRAKING. BUT AT THIS POINT THE BRAKING DIDN'T APPEAR TO BE RESPONDING AND WE CONTINUED TOWARD THE RIGHT OF THE RWY AND WENT OFF IT AT ABOUT 30 KTS. THE GND WAS SOFT FROM A RECENT RAIN, SO WE SANK INTO THE GND FAIRLY QUICKLY AND STOPPED. I DID THE EMER EVAC SHUTDOWN CHK WHILE THE F/O WAS COMMUNICATING WITH THE TWR AND THE PAX. I SENT THE JUMP SEAT PLT BACK TO THE CABIN FOR AN ASSESSMENT OF OUR CONDITION. HE QUICKLY RPTED BACK THAT EVERYTHING APPEARED OK. WE ALSO GOT A RPT FROM THE TWR THAT EVERYTHING LOOKED OK AND THE EMER EQUIP PERSONNEL WHO HAD ALREADY ARRIVED INDICATED NO SERIOUS PROB, SO I DECIDED NOT TO DO AN EMER EVAC AND HAD THE PAX STAY SEATED. LATER WE OPENED THE CABIN DOORS AND EXTENDED THE SLIDES SO PEOPLE COULD GET OFF THE ACFT. BUT AS WE STARTED TO GET PEOPLE OFF, I GOT A REQUEST FROM 1 OF THE EMER PERSONNEL BELOW NOT TO USE THE SLIDES AS A RAMP WAS ON THE WAY. WE STOPPED EXITING PEOPLE VIA THE SLIDES AFTER 13 PEOPLE (OUT OF 116 ABOARD) HAD GOTTEN OFF. THE REST OF THE PEOPLE EXITED VIA THE RAMP STAND BROUGHT TO THE MAIN ENTRANCE. THERE WERE NO APPARENT INJURIES AND ONLY MINOR DAMAGE TO THE ACFT. THIS INCIDENT WAS CAUSED BY A MECHANICAL PROB (LOSS OF HYDS) AND I FEEL EVERYTHING WENT AS PLANNED AND EXPECTED, WITH THE EXCEPTION THAT I WAS SURPRISED TO FIND OUT, EVEN THOUGH WE WERE VERY AWARE WE DIDN'T HAVE NOSE WHEEL STEERING, THAT WE COULDN'T CTL THE ACFT WITH THE USE OF BRAKES, ETC AS WE SLOWED. I HAVE PRACTICED THIS TYPE OF PROB MANY TIMES DURING TRNING AND HAD NOT EXPECTED TO LOSE COMPLETE DIRECTIONAL CTL BEFORE WE STOPPED. IT MAY BE EXPLAINED BY THE FACT THAT IT APPEARS THAT WE MAY HAVE LOST ALL BRAKING NEAR THE END OF THE ROLL. AS WE EXITED THE RWY IT WAS APPARENT THAT WE WERE GOING TO STRIKE A RWY EQUIP BOX, WHICH WAS A VASI BOX. IT LOOKED LIKE IT COULD HAVE CAUSED SOME DAMAGE, BUT IT WAS NOT ANCHORED TOO SECURELY (HOPEFULLY BY DESIGN) AND IT APPARENTLY DID MINIMAL DAMAGE AS IT BROKE AWAY. SUPPLEMENTAL INFO FROM ACN 169528: THERE WAS SOME INITIAL CONFUSION BTWN INFO GIVEN RE: THE EGRESS OF THE PAX. EGRESS SEEMED ORDERLY, EVEN WITH THE SLIGHT CONFUSION RE: THE BACK SLIDES. THE SLIDE ON DOOR 1L JAMMED, APPARENTLY, AND DID NOT DEPLOY.

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.