FLC FAILED TO VERIFY LOAD XPONDER CODE PRIOR TO TKOF. ATC ISSUED XPONDER CODE DURING DEP. FLC REALIZED MISTAKE.

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I AM AN FAA AVIATION SAFETY INSPECTOR (OPS). I OCCUPIED THE FIRST OBSERVER'S JUMP SEAT ON A B747-400 FROM LAX. THE FLC FAILED TO GET AND REVIEW THEIR IFR ENRTE CLRNC PRIOR TO DEP. I AM RATED IN THE B747-400 ACFT. I MAINTAIN CURRENCY AND TAKE A YEARLY PROFICIENCY CHK IN THE B747-400 SIMULATOR. I AM SUPPOSED TO KNOW AND ADHERE TO SOP'S. THEREFORE; I SHARE RESPONSIBILITY FOR THE ERROR. OUR FIRST INDICATION OF THE ERROR CAME AFTER TKOF WHEN THE SOCAL DEP CTLR ASKED THE CREW TO CHK XPONDER AND SQUAWK XXXX; YYYY HAD BEEN SET IN THE XPONDER. THE FO THEN REQUESTED RTE CLRNC THROUGH THE ACARS UNITS. THE CLRNC WAS IDENTICAL TO THE FLT PLAN ENTERED INTO THE FMS; SO NO ATC DEVS OCCURRED. THERE ARE SEVERAL CONTRIBUTING FACTORS. THE CAPT; A HIGHLY EXPERIENCED PLT WITH SEVERAL YRS IN THE B747-400 WAS ON RESERVE AND WAS CALLED OUT 4 HRS PRIOR TO SCHEDULED TKOF. HE ARRIVED AT THE ACFT ABOUT 1 HR BEFORE SCHEDULED PUSHBACK TIME. HE COMPLETED MUCH OF THE COCKPIT SETUP AND PREFLT PROCS; INCLUDING THE WALKAROUND INSPECTION. THE SCHEDULED FO FAILED TO SHOW FOR THE FLT SO A RESERVE FO ARRIVED AT THE ACFT ABOUT 10 MINS AFTER SCHEDULED PUSHBACK TIME. THEREFORE; THERE WAS SOME HASTE TO GET CHKLISTS DONE. THE ACFT PUSHED BACK FROM THE GATE AT XA17. ACR HAS ELABORATE PROCS TO ENSURE THAT THE FLC GETS ITS PREDEP CLRNC. A REF IS ON THE CAPT'S BRIEFING CARD. PROCS APPEAR IN THE B747-400 FLT MANUAL. CREWS SET YYYY IN THE XPONDER AFTER LNDG TO REMIND THE NEXT CREW THAT THEY'LL NEED A CLRNC AND XPONDER CODE. IN THIS CASE; ALL THOSE PROCS FAILED TO PREVENT THE ERROR. SUPPLEMENTAL INFO FROM ACN 542603: WE PUSHED BACK AND TAXIED TO RWY 24L; A RWY I HAVEN'T USED IN YRS! WE BOTH WERE READING THE ABBREVIATED INSTRUCTIONS TO GET TO RWY 24L AND GOT TOTALLY INVOLVED IN TAXIING AND BRIEFING THE DEP PLATE. I LOOKED DOWN AT THE XPONDER AND SAW YYYY. I IMMEDIATELY REALIZED WE HAD NOT GOTTEN OUR PDC.