FLC OF A MIL 4 ENG TURBO PROP FAILED TO LEVEL OFF AT ASSIGNED INTERMEDIATE DEP ALT DUE TO A LACK OF COCKPIT COMS.

Narrative

WE DEPARTED NAS MIRAMAR ON THE JULIAN 9 SID. THE INITIAL LEVEL OFF ALT PASSED TO THE CREW BY CLRNC DEL WAS 11000 FT. AS WE TOOK OFF; WE ENTERED THE CLOUDS AT 2000 FT AND HELD A CLB RATE REQUIRED TO MEET HARD ALTS REQUIRED BY THE SID (IN EXCESS OF 2500 FPM). THE COPLT (PLANE COMMANDER) IN THE R SEAT CHKED IN WITH SAN DIEGO DEP CTL PASSING 3000 FT AND RPTED CLBING TO 11000 FT. UNKNOWN TO THE COPLT; THE PLT'S ICS BOX HAD MALFUNCTIONED; WHICH PRECLUDED ANY INCOMING XMISSIONS FROM ANY RADIO. THE OFF- DUTY PLT WAS ALSO ON HEADSET; BUT COULD NOT HEAR ANY ATC XMISSIONS EITHER; AS HE WAS ALSO PLUGGED INTO THE MALFUNCTIONING BOX. THE COPLT ACKNOWLEDGED A LEVEL OFF ALT OF 7000 FT AND IMMEDIATELY AMENDED ALT OF 5000 FT PASSED BY DEP CTL. HE ASSUMED THAT THE PIC ALSO HEARD THE ALT CHANGES BUT I DID NOT (NEITHER DID THE OFF-DUTY PLT). THE COPLT PASSED THE INFO VERBALLY TO THE REST OF THE COCKPIT CREW; BUT DID NOT SPEAK LOUDLY ENOUGH TO BE HEARD OVER THE ENG NOISE AND RAIN NOISE. ATC CALLED PASSING 5700 FT AND REQUESTED US TO VERIFY ALT. THE COPLT REPLIED WE WERE AT 5700 FT DSNDING TO 5000 FT. ATC THEN PASSED INFO TO ANOTHER ACFT AT 6000 FT. I DO NOT KNOW HOW CLOSE WE CAME TO THE OTHER ACFT. WE CALLED ATC UPON ARR AT NAS WILLOW GROVE AND DISCUSSED THE INCIDENT.