Narrative:

We departed NAS miramar on the julian 9 SID. The initial level off altitude passed to the crew by clearance del was 11000 ft. As we took off, we entered the clouds at 2000 ft and held a climb rate required to meet hard altitudes required by the SID (in excess of 2500 FPM). The copilot (plane commander) in the right seat checked in with san diego departure control passing 3000 ft and reported climbing to 11000 ft. Unknown to the copilot, the pilot's ics box had malfunctioned, which precluded any incoming xmissions from any radio. The off- duty pilot was also on headset, but could not hear any ATC xmissions either, as he was also plugged into the malfunctioning box. The copilot acknowledged a level off altitude of 7000 ft and immediately amended altitude of 5000 ft passed by departure control. He assumed that the PIC also heard the altitude changes but I did not (neither did the off-duty pilot). The copilot passed the information verbally to the rest of the cockpit crew, but did not speak loudly enough to be heard over the engine noise and rain noise. ATC called passing 5700 ft and requested us to verify altitude. The copilot replied we were at 5700 ft descending to 5000 ft. ATC then passed information to another aircraft at 6000 ft. I do not know how close we came to the other aircraft. We called ATC upon arrival at NAS willow grove and discussed the incident.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.