Narrative:

Cabin pressure automatic fail light illuminated during climb through 14000 ft. Followed by a cabin pressure bump and cabin vertical climb indication of over 2000 FPM climb. Cabin pressure annunciator light illuminated and shortly after the cabin oxygen on. Performed cabin pressure automatic fail and cabin pressure loss procedures. Unable to regain automatic pressure control. Returned to departure airport with pressure system in manual mode. Due to small altitude change required, did not accomplish emergency descent. Cabin status was normal and emergency was not declared with ATC. The digital pressure system installed in this aircraft is relatively new. System installation, design and reliability must be questioned to prevent a recurrence of this event. Callback conversation with reporter revealed the following information: the reporter said the aircraft was a DC9-30 with P&west JT8D-9 engines. The reporter stated this airplane was 1 of 2 or 3 airplanes in the carrier's fleet fitted with new digital automatic pressure controllers with air data computer inputs. The reporter said the depressurization was sudden and could not be controled immediately with the manual controller as it took about 75 seconds to gain control manually. The reporter said the airplane was OTS for several days and all system operated normally. The reporter stated it was then discovered the automatic pressure controller was affected by radio frequency interference which was emitted by disbonded DME and TCASII antennas. The reporter said maintenance related to the reporter of another incident of this type that occurred in germany. The reporter said the manufacturer of the automatic pressure controller is unknown.

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Original NASA ASRS Text

Title: A DC9-30 IN CLB AT 14000 FT DIVERTED DUE TO A SUDDEN LOSS OF CABIN PRESSURE DUE TO RADIO FREQ INTERFERENCE CAUSING THE DIGITAL PRESSURE CTLR TO MALFUNCTION.

Narrative: CABIN PRESSURE AUTO FAIL LIGHT ILLUMINATED DURING CLB THROUGH 14000 FT. FOLLOWED BY A CABIN PRESSURE BUMP AND CABIN VERT CLB INDICATION OF OVER 2000 FPM CLB. CABIN PRESSURE ANNUNCIATOR LIGHT ILLUMINATED AND SHORTLY AFTER THE CABIN OXYGEN ON. PERFORMED CABIN PRESSURE AUTO FAIL AND CABIN PRESSURE LOSS PROCS. UNABLE TO REGAIN AUTO PRESSURE CTL. RETURNED TO DEP ARPT WITH PRESSURE SYS IN MANUAL MODE. DUE TO SMALL ALT CHANGE REQUIRED, DID NOT ACCOMPLISH EMER DSCNT. CABIN STATUS WAS NORMAL AND EMER WAS NOT DECLARED WITH ATC. THE DIGITAL PRESSURE SYS INSTALLED IN THIS ACFT IS RELATIVELY NEW. SYS INSTALLATION, DESIGN AND RELIABILITY MUST BE QUESTIONED TO PREVENT A RECURRENCE OF THIS EVENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR SAID THE ACFT WAS A DC9-30 WITH P&W JT8D-9 ENGS. THE RPTR STATED THIS AIRPLANE WAS 1 OF 2 OR 3 AIRPLANES IN THE CARRIER'S FLEET FITTED WITH NEW DIGITAL AUTO PRESSURE CTLRS WITH AIR DATA COMPUTER INPUTS. THE RPTR SAID THE DEPRESSURIZATION WAS SUDDEN AND COULD NOT BE CTLED IMMEDIATELY WITH THE MANUAL CTLR AS IT TOOK ABOUT 75 SECONDS TO GAIN CTL MANUALLY. THE RPTR SAID THE AIRPLANE WAS OTS FOR SEVERAL DAYS AND ALL SYS OPERATED NORMALLY. THE RPTR STATED IT WAS THEN DISCOVERED THE AUTO PRESSURE CTLR WAS AFFECTED BY RADIO FREQ INTERFERENCE WHICH WAS EMITTED BY DISBONDED DME AND TCASII ANTENNAS. THE RPTR SAID MAINT RELATED TO THE RPTR OF ANOTHER INCIDENT OF THIS TYPE THAT OCCURRED IN GERMANY. THE RPTR SAID THE MANUFACTURER OF THE AUTO PRESSURE CTLR IS UNKNOWN.

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.