B737 300 CREW LOST COM WITH ATC BECAUSE OF A STUCK PUSH TO TALK SWITCH IN THE CAPT'S COM SYS.

Narrative

THE FO WAS FLYING TO BWI. CAPT WAS 'RADIO MAN.' WE WERE DSNDING TOWARD SABBI AT 1000 FPM ON THE NOTTINGHAM 5 ARR. WE WERE GIVEN A FREQ CHANGE TO THE LAST WASHINGTON CTR CTLR PRIOR TO POTOMAC APCH. WHEN I ACKNOWLEDGED THE FREQ CHANGE; I KNEW MY 'MIC' WAS STUCK. NEITHER THE FO NOR I COULD XMIT OR HEAR. FIRST; I CHKED THE YOKE SWITCH -- NO HELP. I UNPLUGGED MY HEADSET -- NO HELP. I CHKED THE HAND-HELD MIC -- NO HELP. I FAILED TO NOTICE THAT THE R/T - I/C SWITCH ON THE #1 COM PANEL WAS STUCK IN THE R/T POS. THAT MADE US 'NORDO.' IT'S STRANGE THAT I HAD JUST DISCUSSED THE FUNCTION OF THE 'ALT' SWITCH ON THE COM PANEL. WE SELECTED 'ALT' ON THE FO COM PANEL AND SET THE ATC FREQ ON THE #2 RADIO. I GAVE THE FO THE RADIO JOB. NOW HE IS FLYING AND TALKING. I USED THE AUX HEADSET; SELECTED #2 RADIO ON THE OVERHEAD PANEL AND MONITORED. I HAD LITTLE CONFIDENCE IN MY COM - SO I ELECTED TO LET THE FO FLY AS WELL AS TALK. I MONITORED. ANOTHER COMPLICATION WAS THE BWI WX WAS OVER 200 FT OVERCAST; 1.5 VIS; -RA; ILS 10. I HAD POTOMAC APCH PASS ON WE WERE HAVING RADIO DIFFICULTY SO THEY WOULDN'T BE SURPRISED IF THEY SAW CODE 7700 FOLLOWED BY 7600 AND A LNDG AT BWI. THE FO DID A GREAT JOB. COMPLIMENTS TO HIM. STILL ANOTHER COMPLICATION WAS COMS WITH THE FLT ATTENDANTS. I DIDN'T WANT TO LEAVE THE ATC FREQ; SO WE DIDN'T GIVE A PA. THINGS WERE HAPPENING PRETTY FAST SO I RELIED ON THE 'DING' LEAVING 10000 FT. I LATER EXPLAINED THE SIT ON THE GND. THEY WERE CONCERNED; BUT FIGURED IT OUT. ON THE GND; LIKE USUAL; EVERYTHING WORKED AGAIN. WE CALLED FOR MAINT ANYWAY. I AGAIN CHKED ALL THE SWITCHES AND FOUND THAT THE R/T - I/C SWITCH WOULD STICK WHEN PUSHED TO THE R/T POS. THAT WAS THE CULPRIT. I AM NOT PLEASED WITH MYSELF FOR NOT CATCHING THE SWITCH MALFUNCTION EARLIER. I LOOKED IN THE QRH. THERE IS NO HELP. HAD THIS SIT HAPPENED ENRTE; WE WOULD HAVE HAD MORE TIME TO FIGURE OUT THE PROB. I DON'T KNOW OF ANY PLACE TO PREPARE FOR THIS SIT OTHER THAN EXPERIENCE. I KNOW THAT EVERY LITTLE PROB CAN'T BE REFERENCE TO THE QRH; BUT IT WOULD HAVE HELPED IN THIS SIT. SOME THINGS TO INCLUDE: 1) YOKE SWITCH; 2) HAND SET (MAYBE UNPLUG); 3) R/T - I/C SWITCH (COULD BREAK INTERNALLY) (JAMMED); 4) HEADSET (MAYBE UNPLUG); 5) USE OF COM PANEL ALT/NORMAL SWITCH -- SOME PANELS DON'T HAVE THIS; 6) CIRCUIT BREAKERS; 7) MAY HAVE TO INOP A RADIO IF NOT APPROPRIATE FOR THE QRH; A DISCUSSION OF SOMEWHERE IN THE BOOKS MIGHT BE WORTHY.