Narrative:

While flying the seavu 1 arrival into lax (runway 25L) in a -300 we were cleared for the ILS approach to runway 25L after reaching fuelr (D26.4 lax). I was the PF and toggled from navigation to HSI on the captain's HSI switch. I then selected localizer on the autoplt and deselected LNAV so that the aircraft would track the localizer inbound to runway 25L upon reaching the fuelr intersection. At approximately 7-9 mi; I toggled the HSI switch momentarily to navigation to xchk our position relative to the LNAV course and at that time was distraction by a traffic call. While trying to visually acquire the traffic I failed to notice that the autoplt was not coupled to the localizer when I returned the HSI switch back to 'HSI.' I also failed to notice that the aircraft had drifted north of centerline. When I did notice and started to make the correction back to the localizer centerline for runway 25L; tower called and asked if we were tracking the localizer inbound for runway 25L. We acknowledged that we were north of centerline and were correcting back to the centerline. We were re-established on the centerline at approximately 2500 ft AGL (prior to the limma approach fix) with the correct speed and confign and landed on runway 25L. When flying a -300; it is imperative that the crews be extra vigilant that the LNAV/navigation confign and operation is sufficiently different from the -700 and that airspace deviation's of this sort are more likely to occur. We were flying exclusively -700 aircraft for the previous 2 days and then flew a -300 on the last day of the pairing. In my attempt to gather as much position information in the -300 that is available at a glance in the -700; I failed to notice that the autoplt was not tracking the localizer as I had expected. In the -700 aircraft; crews can simultaneously monitor both without physically repositioning any switches. Crews need to pay extra attention to the 'coupled status' of the autoplt when switching back and forth from HSI to navigation; particularly on approach.

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Original NASA ASRS Text

Title: A B737 PILOT APCHING LAX NOTES THAT B737-300 AND B737-700 MCP (MODE CONTROL PANEL) DIFFERENCES CAN PERMIT A PILOT FLYING THE -300 TO THINK THE LOC IS ACQUIRED WHEN IT IS NOT.

Narrative: WHILE FLYING THE SEAVU 1 ARR INTO LAX (RWY 25L) IN A -300 WE WERE CLRED FOR THE ILS APCH TO RWY 25L AFTER REACHING FUELR (D26.4 LAX). I WAS THE PF AND TOGGLED FROM NAV TO HSI ON THE CAPT'S HSI SWITCH. I THEN SELECTED LOC ON THE AUTOPLT AND DESELECTED LNAV SO THAT THE ACFT WOULD TRACK THE LOC INBOUND TO RWY 25L UPON REACHING THE FUELR INTXN. AT APPROX 7-9 MI; I TOGGLED THE HSI SWITCH MOMENTARILY TO NAV TO XCHK OUR POS RELATIVE TO THE LNAV COURSE AND AT THAT TIME WAS DISTR BY A TFC CALL. WHILE TRYING TO VISUALLY ACQUIRE THE TFC I FAILED TO NOTICE THAT THE AUTOPLT WAS NOT COUPLED TO THE LOC WHEN I RETURNED THE HSI SWITCH BACK TO 'HSI.' I ALSO FAILED TO NOTICE THAT THE ACFT HAD DRIFTED N OF CTRLINE. WHEN I DID NOTICE AND STARTED TO MAKE THE CORRECTION BACK TO THE LOC CTRLINE FOR RWY 25L; TWR CALLED AND ASKED IF WE WERE TRACKING THE LOC INBOUND FOR RWY 25L. WE ACKNOWLEDGED THAT WE WERE N OF CTRLINE AND WERE CORRECTING BACK TO THE CTRLINE. WE WERE RE-ESTABLISHED ON THE CTRLINE AT APPROX 2500 FT AGL (PRIOR TO THE LIMMA APCH FIX) WITH THE CORRECT SPD AND CONFIGN AND LANDED ON RWY 25L. WHEN FLYING A -300; IT IS IMPERATIVE THAT THE CREWS BE EXTRA VIGILANT THAT THE LNAV/NAV CONFIGN AND OP IS SUFFICIENTLY DIFFERENT FROM THE -700 AND THAT AIRSPACE DEV'S OF THIS SORT ARE MORE LIKELY TO OCCUR. WE WERE FLYING EXCLUSIVELY -700 ACFT FOR THE PREVIOUS 2 DAYS AND THEN FLEW A -300 ON THE LAST DAY OF THE PAIRING. IN MY ATTEMPT TO GATHER AS MUCH POS INFO IN THE -300 THAT IS AVAILABLE AT A GLANCE IN THE -700; I FAILED TO NOTICE THAT THE AUTOPLT WAS NOT TRACKING THE LOC AS I HAD EXPECTED. IN THE -700 ACFT; CREWS CAN SIMULTANEOUSLY MONITOR BOTH WITHOUT PHYSICALLY REPOSITIONING ANY SWITCHES. CREWS NEED TO PAY EXTRA ATTN TO THE 'COUPLED STATUS' OF THE AUTOPLT WHEN SWITCHING BACK AND FORTH FROM HSI TO NAV; PARTICULARLY ON APCH.

Data retrieved from NASA's ASRS site as of January 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.