Narrative:

Event occurred on arrival using VNAV descent (forgot to program higher airspeed). VNAV initiated descent out of FL350 at touchdown; all normal until mach/airspeed changeover. At 250 KTS FMC displayed drag device required; at which time I realized my mistake. Speed intervened to increase speed to 290 KTS. At about 260-270 KTS and about FL250 captain's windshield cracked. I immediately reduced speed to 230 KTS and captain directed further reduction to 210 KTS which was maintained until base to final and slowing to configure/land. After the windshield had cracked the captain observed the cabin altitude climbing. Since we were dispatched with 1 pack we concluded this was a result of the idle power descent. Captain directed use of speed brakes in order to increase power in hopes of regaining control of the cabin altitude. The increase power had no apparent effect on cabin altitude/pressurization. The maximum observed cabin altitude was approximately 9500 ft and there was never a cabin altitude warning light. Captain declared an emergency with center. Captain ran the QRH for the cracked windshield (turned off heat). We were both keeping a close eye on the windshield (although I could not see it; after landing captain mentioned he saw sparking at the bottom of the window). Due to the lack of pressurization we tried to maintain 600-700 FPM rate of descent. (There was some differential pressure until sometime below 10000 ft and we knew that eventually the cabin would be descending at the same rate as the aircraft.) ZZZ was landing xxl and we decided that would work since we needed the distance to make our slow descent (we overflew airport for a l-hand visual pattern). At one point on a downwind leg the descent rate did get up to 1500 FPM in an attempt to get down quickly for landing. This rate was slowed to about 600 FPM and downwind extended slightly. An uneventful landing was made and the emergency terminated on clearing the runway. Callback conversation with reporter revealed the following information: reporter had no additional information as to a maintenance resolution of the problem. He did advise the crack in the windshield was an internal pane but there was no obvious indication of air leakage; i.e. No loud hissing as normally associated with any significant loss of air pressure at its source.

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Original NASA ASRS Text

Title: DISPATCHED WITH ONE PACK INOPERATIVE; B767-200 IS UNABLE TO MAINTAIN PRESSURIZATION AFTER SUFFERING A CRACKED WINDSHIELD DURING DESCENT AT FL250.

Narrative: EVENT OCCURRED ON ARR USING VNAV DSCNT (FORGOT TO PROGRAM HIGHER AIRSPD). VNAV INITIATED DSCNT OUT OF FL350 AT TOUCHDOWN; ALL NORMAL UNTIL MACH/AIRSPD CHANGEOVER. AT 250 KTS FMC DISPLAYED DRAG DEVICE REQUIRED; AT WHICH TIME I REALIZED MY MISTAKE. SPD INTERVENED TO INCREASE SPD TO 290 KTS. AT ABOUT 260-270 KTS AND ABOUT FL250 CAPT'S WINDSHIELD CRACKED. I IMMEDIATELY REDUCED SPD TO 230 KTS AND CAPT DIRECTED FURTHER REDUCTION TO 210 KTS WHICH WAS MAINTAINED UNTIL BASE TO FINAL AND SLOWING TO CONFIGURE/LAND. AFTER THE WINDSHIELD HAD CRACKED THE CAPT OBSERVED THE CABIN ALT CLBING. SINCE WE WERE DISPATCHED WITH 1 PACK WE CONCLUDED THIS WAS A RESULT OF THE IDLE PWR DSCNT. CAPT DIRECTED USE OF SPD BRAKES IN ORDER TO INCREASE PWR IN HOPES OF REGAINING CTL OF THE CABIN ALT. THE INCREASE PWR HAD NO APPARENT EFFECT ON CABIN ALT/PRESSURIZATION. THE MAX OBSERVED CABIN ALT WAS APPROX 9500 FT AND THERE WAS NEVER A CABIN ALT WARNING LIGHT. CAPT DECLARED AN EMER WITH CTR. CAPT RAN THE QRH FOR THE CRACKED WINDSHIELD (TURNED OFF HEAT). WE WERE BOTH KEEPING A CLOSE EYE ON THE WINDSHIELD (ALTHOUGH I COULD NOT SEE IT; AFTER LNDG CAPT MENTIONED HE SAW SPARKING AT THE BOTTOM OF THE WINDOW). DUE TO THE LACK OF PRESSURIZATION WE TRIED TO MAINTAIN 600-700 FPM RATE OF DSCNT. (THERE WAS SOME DIFFERENTIAL PRESSURE UNTIL SOMETIME BELOW 10000 FT AND WE KNEW THAT EVENTUALLY THE CABIN WOULD BE DSNDING AT THE SAME RATE AS THE ACFT.) ZZZ WAS LNDG XXL AND WE DECIDED THAT WOULD WORK SINCE WE NEEDED THE DISTANCE TO MAKE OUR SLOW DSCNT (WE OVERFLEW ARPT FOR A L-HAND VISUAL PATTERN). AT ONE POINT ON A DOWNWIND LEG THE DSCNT RATE DID GET UP TO 1500 FPM IN AN ATTEMPT TO GET DOWN QUICKLY FOR LNDG. THIS RATE WAS SLOWED TO ABOUT 600 FPM AND DOWNWIND EXTENDED SLIGHTLY. AN UNEVENTFUL LNDG WAS MADE AND THE EMER TERMINATED ON CLRING THE RWY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER HAD NO ADDITIONAL INFORMATION AS TO A MAINT RESOLUTION OF THE PROBLEM. HE DID ADVISE THE CRACK IN THE WINDSHIELD WAS AN INTERNAL PANE BUT THERE WAS NO OBVIOUS INDICATION OF AIR LEAKAGE; I.E. NO LOUD HISSING AS NORMALLY ASSOCIATED WITH ANY SIGNIFICANT LOSS OF AIR PRESSURE AT ITS SOURCE.

Data retrieved from NASA's ASRS site as of May 2009 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.