A B737-700 FLT CREW EXPERIENCES A LOSS OF 2-WAY COM WITH TWR AND DEP CTL; RESORTING TO A XPONDER CODE OF 7700 WHILE FLYING THE LOST COM PROC OUT OF LAX; CA.

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DEPARTED LAX ON GMN4 DEP FROM RWY 24L; CAPT'S LEG. ON INITIAL CLB; WE NOTICED TWR DIDN'T HAND US OFF TO DEP CTL. WHEN I ASKED TWR FOR HDOF; WE GOT NO REPLY; AND ALSO HEARD NO OTHER RADIO TFC. THE CAPT TRIED HIS RADIO WITH NO LUCK. WE LEVELED AT 3000 FT PER THE DEP AND CONTINUED HEADING 250 DEGS AND LOOKED AT THE LOST COM PROCS ON THE DEP PLACE. WE RECALLED A PREVIOUS WRITE-UP ABOUT THE RADIOS AND TRIED ALL COMBINATIONS OF RADIOS AND MIKES MAKING CALLS IN THE BLIND. WE SQUAWKED 7700 INITIALLY WITH THE INTENTION OF SWITCHING TO 7600 AFTER A MIN; BUT IN THE CONFUSION; FORGOT TO SWITCH TO 7600. AFTER A FEW MINS AND MUCH SEEMINGLY FUTILE EFFORT; WE REGAINED RADIOS WITH THE CAPT TALKING ON RADIO #2 USING HIS HAND MIKE. AT THAT POINT; THE CAPT WORKED THE RADIOS; AND I FLEW. WE WERE ABLE TO TALK TO DEP CTL LONG ENOUGH TO GET A TURN TO 020 DEGS AND A CLB TO 9000 FT. THE CTLR SAID WE'D HAD A STUCK MIKE. THEY ALSO TOLD US TO GO BACK TO OUR ORIGINAL SQUAWK. SHORTLY AFTER MAKING OUR TURN TO 020 DEGS; WE LOST CONTACT AGAIN. HAVING JUST COME FROM SMF THE PREVIOUS LEG; WE DECIDED AGAINST TURNING BACK TO LAX WITHOUT RADIOS; AND MADE XMISSIONS IN THE BLIND THAT WE WERE CLBING TO FL230 AND CONTINUING THE DEP PROC. WE WERE PRETTY SURE OUR MIKES WERE NOT STUCK; BUT FIGURED SINCE SOCAL SEEMED TO THINK THEY WERE; OUR RADIO XMISSIONS WERE AT LEAST BEING HEARD AND WE JUST WEREN'T RECEIVING. APCHING FL200; WE REGAINED CONTACT ONCE AGAIN WITH THE CAPT USING HIS HAND MIKE WITH THE #2 RADIO IN THE ALTERNATE POS. WE DIDN'T TOUCH ANOTHER RADIO CTL FOR THE REST OF THE FLT AND WERE ABLE TO MAINTAIN RADIO CONTACT. ATC ASKED US TO VERIFY OUR COCKPIT WAS SECURE; WHICH REALLY GOT OUR ATTN AS WE THOUGHT ABOUT WHAT MIGHT HAVE HAPPENED IF WE'D TURNED BACK TOWARD LAX WITHOUT COM. LESSONS LEARNED: 1) PAY ATTN TO THE LOST COM PROCS ON THE DEP AND ARR PLATES. WE'VE GOT MULTIPLE RADIOS; BUT A FAILURE SOMEWHERE PREVENTED EITHER OF US FROM HEARING INCOMING RADIO TFC. 2) WE WERE SO BUSY WITH THE RADIOS; LOST COM PROCS; AND FLYING THE AIRPLANE THAT WE FELL BACK ON OLD HABITS AND PUT 7700 IN THE XPONDER; THEN FORGOT AND LEFT IT THERE. ALTHOUGH ATC COULD HEAR OUR XMISSIONS; IT STILL GOT THEIR ATTN. 3) FLY THE AIRPLANE. I THINK WE DID A PRETTY GOOD JOB OF THAT. THE CAPT GAVE ME THE AIRPLANE TO FLY WHILE HE WORKED THE RADIOS IN A SIT THAT COULD EASILY HAVE HAD BOTH OF US HEADS DOWN FOR A LONG PERIOD OF TIME. SUPPLEMENTAL IN FROM ACN 590244: WE LEVELED AT 3000 FT AND 250 KTS AND BEGAN TIMING IN ORDER TO FLY THE PUBLISHED LOST COM PROC. WE CONTINUED TO MAKE CALLS IN THE BLIND; STATING OUR INTENTIONS; AND CAREFULLY MONITORED TCASII. AS FORMER MIL PLTS; WE REFLEXIVELY SET 7700 FOR 1 MIN IN PREPARATION FOR SETTING 7600 IN THE XPONDER. AFTER 5 MINS; BRIEFLY REGAINED RADIO CONTACT; BUT LOST IT AFTER 10-15 SECONDS. DISCUSSED GOING VFR AND RETURNING TO DEP ARPT (LAX) WITH LOST COMS PER FOM RECOMMENDATION. DECIDED THAT PROCEEDING TO OUR NEXT CITY WAS THE BEST OPTION; AS WE KNOW THE RTE AND FIELD TO BE CAVU AND LEVELING AT CRUISE ALT WOULD GIVE US TIME TO COORDINATE CLRNCS; GATES; ETC; VIA OUR ACARS TO DISPATCH TO ATC. DISCUSSED THE 7700 CODE VERSUS FOM RECOMMENDATION OF GOING STRAIGHT TO 7600 FOR LOST COM. IN THE FUTURE I WILL OMIT 7700 AND GO STRAIGHT TO 7600. AT NO TIME WAS ACFT SEPARATION LOST.