PROBABLE LAND WITHOUT CLRNC. ACCORDING TO THE FO; THE FLT WAS CLRED TO LAND AND HE HIT THE TRANSFER SWITCH BY MISTAKE WHEN SETTING IN GND CTL FREQ. AFTER LNDG AND HOLDING SHORT OF RWY; APCH CTLR ADVISED FLC TO CONTACT TWR.

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FOR APCH AND LNDG AT LAX THE CAPT WAS FLYING; FO WAS RADIO COM; AND A RELIEF PLT WAS ON THE FLT DECK. AFTER UNEVENTFUL LNDG; WE TURNED OFF LAX RWY 25L AND HELD SHORT OF RWY 25R AT INTXN M. AT THAT POINT WE RECEIVED A RADIO CALL TO HOLD SHORT OF RWY 25R; CONTACT TWR. ONE OF TWO POSSIBILITIES HAD OCCURRED; AND THE CREW IS NOT SURE WHICH. EITHER WE LANDED WITHOUT CLRNC; OR AFTER RECEIVING CLRNC; THE FO; INTENDING TO PRETUNE GND CTL FREQ; INADVERTENTLY LEFT TWR FREQ. ALL CHKLISTS AND PROCS WERE FOLLOWED; AND THERE WAS NOTHING UNUSUAL OR RUSHED ABOUT THE APCH AND LNDG. AT 1000 FT AGL FO CALLED OUT '1000 FT; INST XCHK.' CAPT RESPONDED 'ROGER; CLRED TO LAND.' I RESPONDED; CONFIDENT THAT CLRNC HAD BEEN RECEIVED; AND IN THE PAST I'VE NEVER BEEN SHY ABOUT CONFIRMING LNDG CLRNC. I BELIEVE THE PROCS AND CALLOUTS CONTAINED IN SOP ARE ADEQUATE FOR PREVENTING LNDG WITHOUT CLRNC. I ALSO BELIEVE THAT FACTORS AFFECTING THE CREW DURING THIS FLT - - SUCH AS FATIGUE AFTER THE 6 DAY TRIP; THE 12 HR FLT; OR PREOCCUPATION WITH THE DRUG TEST WE'D BEEN ADVISED TO EXPECT AFTER LNDG -- WERE NOT SEVERE ENOUGH TO EXPLAIN THE EVENT. IT SEEMS THAT ONE OF THOSE EVENTS THAT COULDN'T HAPPEN TO ME; HAS. ALTHOUGH IT IS POSSIBLE THE RADIO WAS DE-TUNED AFTER RECEIPT OF CLRNC; I THINK THAT IS UNLIKELY. BETTER TO CONCENTRATE ON PREVENTING LNDG WITHOUT CLRNC; AND ESPECIALLY ON BEING SURE THAT CLRNC HAS BEEN RECEIVED BEFORE RESPONDING TO THE 1000 FT CALL. SUPPLEMENTAL INFO FROM ACN 341180: TWR GAVE US CLRED TO LAND; AND AS I WAS SAYING CLRED TO LAND; I HIT THE TRANSFER SWITCH BY MISTAKE WHICH PUT US BACK ON APCH FREQ.