Narrative:

Passing FL260, pressurization wasn't stopping at 8.6 psi differential. Leveled aircraft at FL280. So pulled out red tab emergency procedures and started through checklist with captain (first officer flying). Started a descent down to 16000 ft. Completed red tab checklist, pressurization in manual dc mode. Pressurization responded to opening/closing of manual outflow control valve, setting was 1000 FPM rate of descent. Captain noticed a faint electrical smell, first officer and so did not. Approximately 1 min later all 3 crew members noticed a strong electrical burning smell. All 3 crew members went on oxygen. Declared an emergency with ZNY and did a visual approach to runway 31 at mdt. Had the emergency ground crew do a visual walkaround of the aircraft and they found no sign of smoke or fumes coming from aircraft. Shut down #3 engine, taxi aircraft into the ramp for a shutdown. Had no fumes in aircraft during the taxi or during the shutdown. Callback conversation with reporter revealed the following information: the reporter stated the smoke, when it became more noticeable, was coming from behind the pressurization control panel. The reporter said it appeared after the pressurization system was switched to manual dc. The reporter said maintenance found charred and burned wiring connected to the pressurization panel and it's believed to be in the manual dc circuit. The reporter stated no circuit breakers were tripped.

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Original NASA ASRS Text

Title: A B727-200 IN CRUISE AT FL280 DECLARED AN EMER DUE TO LOSS OF PRESSURIZATION AND SMOKE FROM BEHIND PRESSURIZATION CTL PANEL.

Narrative: PASSING FL260, PRESSURIZATION WASN'T STOPPING AT 8.6 PSI DIFFERENTIAL. LEVELED ACFT AT FL280. SO PULLED OUT RED TAB EMER PROCS AND STARTED THROUGH CHKLIST WITH CAPT (FO FLYING). STARTED A DSCNT DOWN TO 16000 FT. COMPLETED RED TAB CHKLIST, PRESSURIZATION IN MANUAL DC MODE. PRESSURIZATION RESPONDED TO OPENING/CLOSING OF MANUAL OUTFLOW CTL VALVE, SETTING WAS 1000 FPM RATE OF DSCNT. CAPT NOTICED A FAINT ELECTRICAL SMELL, FO AND SO DID NOT. APPROX 1 MIN LATER ALL 3 CREW MEMBERS NOTICED A STRONG ELECTRICAL BURNING SMELL. ALL 3 CREW MEMBERS WENT ON OXYGEN. DECLARED AN EMER WITH ZNY AND DID A VISUAL APCH TO RWY 31 AT MDT. HAD THE EMER GND CREW DO A VISUAL WALKAROUND OF THE ACFT AND THEY FOUND NO SIGN OF SMOKE OR FUMES COMING FROM ACFT. SHUT DOWN #3 ENG, TAXI ACFT INTO THE RAMP FOR A SHUTDOWN. HAD NO FUMES IN ACFT DURING THE TAXI OR DURING THE SHUTDOWN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE SMOKE, WHEN IT BECAME MORE NOTICEABLE, WAS COMING FROM BEHIND THE PRESSURIZATION CTL PANEL. THE RPTR SAID IT APPEARED AFTER THE PRESSURIZATION SYS WAS SWITCHED TO MANUAL DC. THE RPTR SAID MAINT FOUND CHARRED AND BURNED WIRING CONNECTED TO THE PRESSURIZATION PANEL AND IT'S BELIEVED TO BE IN THE MANUAL DC CIRCUIT. THE RPTR STATED NO CIRCUIT BREAKERS WERE TRIPPED.

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.