Narrative:

I was the PF and we were descending on a vector to join the localizer 27 approach at san. Ceilings were near minimums for the localizer approach and we had briefed a company procedures approach -- first officer flying and captain landing. My last act as PF was to set the aircraft up for an LNAV intercept to the 27 localizer outside of swatt. I gave the aircraft to the first officer and he was aware of the flight mode selections. While not specifically briefed; I believed he was aware of the initial plan to fly the localizer course in LNAV mode (due to the notoriously wandering localizer for this runway) with the idea of switching to localizer mode on the MCP prior to the FAF. I should have made this clearer in my briefing; because neither of us caught that LNAV was still selected as we began our descent inside reebo. Just as we were approaching the MDA and breaking out of the overcast; the tower controller reported a low altitude alert on us. At that same time I acquired the runway; but was surprised to see it over at about the 1:30 O'clock position. A quick glance at the HSI needle (still showing raw localizer data since we were flying a -700) indeed showed us a little more than 1 DOT left of course. I took over flying and the first officer acknowledged the tower's advisory. I disconnected the autoplt and made a correction back to the runway centerline. The rest of the approach and landing were stabilized and uneventful. No egpws warnings/cautions were observed throughout the approach. I need to follow the company procedures for LNAV transitions to instrument approachs; even if it means some hunting of the aircraft when tracking locs like runway 27 at san.

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Original NASA ASRS Text

Title: B737 CAPT REPORTS INADVERTENTLY USING LNAV TO FLY LOC RWY 27 AT SAN.

Narrative: I WAS THE PF AND WE WERE DSNDING ON A VECTOR TO JOIN THE LOC 27 APCH AT SAN. CEILINGS WERE NEAR MINIMUMS FOR THE LOC APCH AND WE HAD BRIEFED A COMPANY PROCS APCH -- FO FLYING AND CAPT LNDG. MY LAST ACT AS PF WAS TO SET THE ACFT UP FOR AN LNAV INTERCEPT TO THE 27 LOC OUTSIDE OF SWATT. I GAVE THE ACFT TO THE FO AND HE WAS AWARE OF THE FLT MODE SELECTIONS. WHILE NOT SPECIFICALLY BRIEFED; I BELIEVED HE WAS AWARE OF THE INITIAL PLAN TO FLY THE LOC COURSE IN LNAV MODE (DUE TO THE NOTORIOUSLY WANDERING LOC FOR THIS RWY) WITH THE IDEA OF SWITCHING TO LOC MODE ON THE MCP PRIOR TO THE FAF. I SHOULD HAVE MADE THIS CLEARER IN MY BRIEFING; BECAUSE NEITHER OF US CAUGHT THAT LNAV WAS STILL SELECTED AS WE BEGAN OUR DSCNT INSIDE REEBO. JUST AS WE WERE APCHING THE MDA AND BREAKING OUT OF THE OVCST; THE TWR CTLR RPTED A LOW ALT ALERT ON US. AT THAT SAME TIME I ACQUIRED THE RWY; BUT WAS SURPRISED TO SEE IT OVER AT ABOUT THE 1:30 O'CLOCK POS. A QUICK GLANCE AT THE HSI NEEDLE (STILL SHOWING RAW LOC DATA SINCE WE WERE FLYING A -700) INDEED SHOWED US A LITTLE MORE THAN 1 DOT L OF COURSE. I TOOK OVER FLYING AND THE FO ACKNOWLEDGED THE TWR'S ADVISORY. I DISCONNECTED THE AUTOPLT AND MADE A CORRECTION BACK TO THE RWY CTRLINE. THE REST OF THE APCH AND LNDG WERE STABILIZED AND UNEVENTFUL. NO EGPWS WARNINGS/CAUTIONS WERE OBSERVED THROUGHOUT THE APCH. I NEED TO FOLLOW THE COMPANY PROCS FOR LNAV TRANSITIONS TO INST APCHS; EVEN IF IT MEANS SOME HUNTING OF THE ACFT WHEN TRACKING LOCS LIKE RWY 27 AT SAN.

Data retrieved from NASA's ASRS site as of May 2009 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.