Narrative:

I picked up the aircraft from the maintenance facility. Upon a hurried departure, the co-pilot started the checklist at 'starting engines' rather than at 'before starting engines,' consequently missing the bleed air switches in the off position. The aircraft pressurized normally and the flight at FL410 en route to ZZZ was uneventful until the decent portion. ZZZ center requested we expedite from FL290 to FL240, at which time the engines were retarded to flight idle. At this time the cabin attendant began to climb rapidly. We elected to execute an emergency decent to 10000 ft and advised center. Upon reaching 10000 ft and reviewing switch positions, it was discovered that the bleed air switches were in the off position. Setting the bleed air switches to the on position, the pressurization system functioned normally, and flight continued to destination. Upon investigation on ground at home base, it was discovered that malfunctioning valves allowed the aircraft to pressurize although the bleed switches were in the off position. Apparently the power reduction at FL290 caused the valve momentarily to switch, resulting in loss of pressurized air to the cabin. Callback conversation with reporter revealed the following information: the reporter stated the airplane was picked up at the maintenance facility and reported done complete. The reporter said the checklist was ran through and the 'before engine start' checklist was not accomplished. The reporter said the airplane pressurized normally during cruise at FL410 and only at descent with the throttles pulled back to flight idle was pressurization lost. The reporter stated it was only after the emergency descent was it noted the engine pneumatic bleed control switches were in the 'off' position. The reporter said maintenance found one failed bleed valve which was replaced and on the other engine, the bleed valve electrical connector was not connected.

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Original NASA ASRS Text

Title: A LEAR 31 ON DSCNT AT FL290 WITH THROTTLES AT FLT IDLE THE CABIN BEGAN TO CLB RAPIDLY. EMER DSCNT TO 10000 FT REGAINED PRESSURIZATION.

Narrative: I PICKED UP THE ACFT FROM THE MAINT FACILITY. UPON A HURRIED DEP, THE CO-PLT STARTED THE CHKLIST AT 'STARTING ENGS' RATHER THAN AT 'BEFORE STARTING ENGS,' CONSEQUENTLY MISSING THE BLEED AIR SWITCHES IN THE OFF POSITION. THE ACFT PRESSURIZED NORMALLY AND THE FLT AT FL410 ENRTE TO ZZZ WAS UNEVENTFUL UNTIL THE DECENT PORTION. ZZZ CENTER REQUESTED WE EXPEDITE FROM FL290 TO FL240, AT WHICH TIME THE ENGS WERE RETARDED TO FLT IDLE. AT THIS TIME THE CAB BEGAN TO CLB RAPIDLY. WE ELECTED TO EXECUTE AN EMER DECENT TO 10000 FT AND ADVISED CENTER. UPON REACHING 10000 FT AND REVIEWING SWITCH POSITIONS, IT WAS DISCOVERED THAT THE BLEED AIR SWITCHES WERE IN THE OFF POSITION. SETTING THE BLEED AIR SWITCHES TO THE ON POSITION, THE PRESSURIZATION SYSTEM FUNCTIONED NORMALLY, AND FLT CONTINUED TO DESTINATION. UPON INVESTIGATION ON GND AT HOME BASE, IT WAS DISCOVERED THAT MALFUNCTIONING VALVES ALLOWED THE ACFT TO PRESSURIZE ALTHOUGH THE BLEED SWITCHES WERE IN THE OFF POSITION. APPARENTLY THE POWER REDUCTION AT FL290 CAUSED THE VALVE MOMENTARILY TO SWITCH, RESULTING IN LOSS OF PRESSURIZED AIR TO THE CABIN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE AIRPLANE WAS PICKED UP AT THE MAINT FACILITY AND RPTED DONE COMPLETE. THE RPTR SAID THE CHKLIST WAS RAN THROUGH AND THE 'BEFORE ENG START' CHKLIST WAS NOT ACCOMPLISHED. THE RPTR SAID THE AIRPLANE PRESSURIZED NORMALLY DURING CRUISE AT FL410 AND ONLY AT DSCNT WITH THE THROTTLES PULLED BACK TO FLT IDLE WAS PRESSURIZATION LOST. THE RPTR STATED IT WAS ONLY AFTER THE EMER DSCNT WAS IT NOTED THE ENG PNEUMATIC BLEED CTL SWITCHES WERE IN THE 'OFF' POSITION. THE RPTR SAID MAINT FOUND ONE FAILED BLEED VALVE WHICH WAS REPLACED AND ON THE OTHER ENG, THE BLEED VALVE ELECTRICAL CONNECTOR WAS NOT CONNECTED.

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.