Narrative:

Prior to beginning the run-up for originating flight xxy out of ZZZ2, I consulted a mechanic (our airline) in person regarding apparent delamination of the captain's forward windshield. The unusually large delamination was in the bottom right corner, measuring approximately 4 inches high and 1 1/2 inches wide. It did not interfere with my vision out the window, however, and the mechanic advised me that because of that fact a write-up in the maintenance log was not required (since this was not considered a discrepancy). The mechanic studied the suspect area both in the interior and exterior before giving me his recommendation, however, his evaluation may have been made more difficult due to the poor lighting conditions on the dark ramp. Later, during climb out on the first leg of the morning, as we were approaching FL210 and the cabin pressure differential reached close to 5 psi, we heard a loud pop as 1 ply of the windshield shattered completely, with spider webbing so extensive I could not see outside it very well. The first officer was flying, so I directed him to stop climbing and begin a descent to 10000 ft in order to reduce the cabin pressure differential. I then informed center of our situation and requested an immediate descent to 10000 ft and a return to our departure airport. A descent was immediately cleared to something like 14000 ft or so, with subsequent lower altitudes before leveloff., since our request for descent was immediately granted, I felt the use of any emergency authority/authorized was not immediately required. The aircraft was maintaining cabin pressure as well, so oxygen use was not required. During our descent, I contacted dispatch and informed them of our situation. Up until this point I had not declared an emergency with ATC. However, the dispatcher expressed concern over my not being able to see outside for traffic and point out any deviations as the first officer landed the airplane. He said he would declare an emergency and have crash fire rescue equipment standing by in ZZZ2. I agreed and declared an emergency as well with ATC for the same reasons. An uneventful landing in ZZZ2 was made, and I elected to have the first officer taxi to the gate. I decided not to terminate the emergency until we were parked, since I could not see forward very well as the first officer taxied. Ground control was notified of the termination of our emergency when we arrived at the gate.

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Original NASA ASRS Text

Title: A BE1900D IN CLB AT FL210 DECLARED AN EMER AND DIVERTED DUE TO THE CAPT'S WINDSHIELD SHATTERING.

Narrative: PRIOR TO BEGINNING THE RUN-UP FOR ORIGINATING FLT XXY OUT OF ZZZ2, I CONSULTED A MECH (OUR AIRLINE) IN PERSON REGARDING APPARENT DELAMINATION OF THE CAPT'S FORWARD WINDSHIELD. THE UNUSUALLY LARGE DELAMINATION WAS IN THE BOTTOM R CORNER, MEASURING APPROX 4 INCHES HIGH AND 1 1/2 INCHES WIDE. IT DID NOT INTERFERE WITH MY VISION OUT THE WINDOW, HOWEVER, AND THE MECH ADVISED ME THAT BECAUSE OF THAT FACT A WRITE-UP IN THE MAINT LOG WAS NOT REQUIRED (SINCE THIS WAS NOT CONSIDERED A DISCREPANCY). THE MECH STUDIED THE SUSPECT AREA BOTH IN THE INTERIOR AND EXTERIOR BEFORE GIVING ME HIS RECOMMENDATION, HOWEVER, HIS EVALUATION MAY HAVE BEEN MADE MORE DIFFICULT DUE TO THE POOR LIGHTING CONDITIONS ON THE DARK RAMP. LATER, DURING CLBOUT ON THE FIRST LEG OF THE MORNING, AS WE WERE APCHING FL210 AND THE CABIN PRESSURE DIFFERENTIAL REACHED CLOSE TO 5 PSI, WE HEARD A LOUD POP AS 1 PLY OF THE WINDSHIELD SHATTERED COMPLETELY, WITH SPIDER WEBBING SO EXTENSIVE I COULD NOT SEE OUTSIDE IT VERY WELL. THE FO WAS FLYING, SO I DIRECTED HIM TO STOP CLBING AND BEGIN A DSCNT TO 10000 FT IN ORDER TO REDUCE THE CABIN PRESSURE DIFFERENTIAL. I THEN INFORMED CTR OF OUR SIT AND REQUESTED AN IMMEDIATE DSCNT TO 10000 FT AND A RETURN TO OUR DEP ARPT. A DSCNT WAS IMMEDIATELY CLRED TO SOMETHING LIKE 14000 FT OR SO, WITH SUBSEQUENT LOWER ALTS BEFORE LEVELOFF., SINCE OUR REQUEST FOR DSCNT WAS IMMEDIATELY GRANTED, I FELT THE USE OF ANY EMER AUTH WAS NOT IMMEDIATELY REQUIRED. THE ACFT WAS MAINTAINING CABIN PRESSURE AS WELL, SO OXYGEN USE WAS NOT REQUIRED. DURING OUR DSCNT, I CONTACTED DISPATCH AND INFORMED THEM OF OUR SIT. UP UNTIL THIS POINT I HAD NOT DECLARED AN EMER WITH ATC. HOWEVER, THE DISPATCHER EXPRESSED CONCERN OVER MY NOT BEING ABLE TO SEE OUTSIDE FOR TFC AND POINT OUT ANY DEVS AS THE FO LANDED THE AIRPLANE. HE SAID HE WOULD DECLARE AN EMER AND HAVE CFR STANDING BY IN ZZZ2. I AGREED AND DECLARED AN EMER AS WELL WITH ATC FOR THE SAME REASONS. AN UNEVENTFUL LNDG IN ZZZ2 WAS MADE, AND I ELECTED TO HAVE THE FO TAXI TO THE GATE. I DECIDED NOT TO TERMINATE THE EMER UNTIL WE WERE PARKED, SINCE I COULD NOT SEE FORWARD VERY WELL AS THE FO TAXIED. GND CTL WAS NOTIFIED OF THE TERMINATION OF OUR EMER WHEN WE ARRIVED AT THE GATE.

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.