A G1159A (GIII) pressurization control panel failed at FL270. An emergency descent followed but ATC could not hear the pilot because of cockpit noise. The problem was traced to the pressurization control panel canon plug.

Narrative

During the climb to FL410; cabin pressure was noticed reading 19900 ft out of FL270. Both pilots went on oxygen and the aircraft was leveled at FL270. Attempts to operate the pressurization system in manual failed and a rapid decent was initiated to 10000 ft. No descent clearance was received prior to executing the descent. It seems that center could not hear us via the oxygen mask microphones or via the handheld microphone. Further troubleshooting of the problem indicated that the entire pressurization indication panel was inoperative. Being a totally digital setup; the cabin altitude read 19900 ft; the cabin differential pressure read zero; and the rate of climb read zero. Had a backup gauge of any sort been available; preferably an analog gauge; the entire problem could have been avoided.Callback conversation with reporter revealed the following information: The reporter states that the pressurization control panel was completely inoperative. The cabin altitude warning horn did sound after the panel's failure. An examination of the pressurization control panel canon plug connector revealed pin corrosion preventing adequate electrical contact. The ATC communication failure was apparently the result of high ambient cockpit noise during the descent.