Narrative:

During initial cruise climb out the first officer and I heard a popping/crack sound from the left aft side window passing approximately FL276 on our way to FL350. Our inspection revealed a significant multi-layered area of delamination and a thread size 5-6 inch vertical possible crack in the delamination area. We contacted ATC; stopped our climb at FL290 and previewed the QRH; contacted dispatch; maintenance and operations manager via ACARS and sat phone to consult. Maintenance control recommended following QRH as a precaution and requested a return. As applying QRH abnormal section would address the matter for safety; the 'possible crack' couldn't be confirmed as one; nor did it or the delamination increase in size and no further noise occurred; we concurred with a safe return to our departure airport. We then requested routing and lower than FL230 from ATC. Notified the cabin crew of situation and details and PA to guests. ATC issued a left turn for initial vectors and a descent to FL240. Although ATC was aware we were trouble shooting/running a checklist; previous possible and current request to return and we needed lower than the FL240 they had assigned; there were lengthy delays in getting lower. Several aircraft were blocking our; each others; and multiple ATC transmissions. ATC seemed task saturated and during this time and we were rather busy also. The lead flight attendant called the cockpit to provide us some info regarding their progress and a question I answered him; explained we were very busy at the time and would call him back in a few minutes; concurrently our stable cabin climb was approaching 8000 cabin alt per the QRH with a climb rate set at 700-750 FPM. We received a momentary cabin altitude ECAM and noted the cabin climb rate had jumped to approximately 1700 FPM (no crew inputs on toggle) showing a cabin alt of 8850. As a precaution we complied with the ECAM; declared an emergency descent (total of approsimately 50-60 seconds) and rectified the cabin bump in altitude by going to auto mode as the manual mode obviously got finicky. ATC acknowledged our descent after repeated calls as were approaching FL233 and asked if we could accept FL180. As the ECAM message resolved already; we accepted FL180 and I canceled our emergency status at this time. Further manual mode operation was uneventful with only minor; now expected; bumps in vertical speed from 0 FPM to 500 FPM to 0 FPM every 5-10 minutes. We burned excess fuel with delay vectors in the arrival area for approximately 45 minutess to preclude an overweight landing with dispatcher concurrence. Normal landing ensued at our departure airport. Maintenance inspected aircraft for approximately 50 minutes and initially said the window had to be replaced. After additional inspection maintenance returned aircraft to service noting the area was just within limits. Flight continued to our destination normally. Suggest loft training for pilot group utilizing manual vertical speed control for a leg. The system is a little fussy in manual and the design is unusual in that one can't set a target cabin altitude.

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Original NASA ASRS Text

Title: An A320 flight crew experienced left aft side cockpit window delamination in climb. They coordinated with company; declared an emergency; descended to a lower altitude; and returned to their departure airport.

Narrative: During initial cruise climb out the First Officer and I heard a popping/crack sound from the left aft side window passing approximately FL276 on our way to FL350. Our inspection revealed a significant multi-layered area of delamination and a thread size 5-6 inch vertical possible crack in the delamination area. We contacted ATC; stopped our climb at FL290 and previewed the QRH; contacted Dispatch; Maintenance and Operations Manager via ACARS and sat phone to consult. Maintenance Control recommended following QRH as a precaution and requested a return. As applying QRH Abnormal Section would address the matter for safety; the 'possible crack' couldn't be confirmed as one; nor did it or the delamination increase in size and no further noise occurred; we concurred with a safe return to our departure airport. We then requested routing and lower than FL230 from ATC. Notified the cabin crew of situation and details and PA to guests. ATC issued a left turn for initial vectors and a descent to FL240. Although ATC was aware we were trouble shooting/running a checklist; previous possible and current request to return and we needed lower than the FL240 they had assigned; there were lengthy delays in getting lower. Several aircraft were blocking our; each others; and multiple ATC transmissions. ATC seemed task saturated and during this time and we were rather busy also. The Lead Flight Attendant called the cockpit to provide us some info regarding their progress and a question I answered him; explained we were very busy at the time and would call him back in a few minutes; concurrently our stable cabin climb was approaching 8000 cabin alt per the QRH with a climb rate set at 700-750 FPM. We received a momentary cabin altitude ECAM and noted the cabin climb rate had jumped to approximately 1700 FPM (no crew inputs on toggle) showing a cabin alt of 8850. As a precaution we complied with the ECAM; declared an emergency descent (total of approsimately 50-60 seconds) and rectified the cabin bump in altitude by going to auto mode as the manual mode obviously got finicky. ATC acknowledged our descent after repeated calls as were approaching FL233 and asked if we could accept FL180. As the ECAM message resolved already; we accepted FL180 and I canceled our emergency status at this time. Further manual mode operation was uneventful with only minor; now expected; bumps in vertical speed from 0 FPM to 500 FPM to 0 FPM every 5-10 minutes. We burned excess fuel with delay vectors in the arrival area for approximately 45 minutess to preclude an overweight landing with dispatcher concurrence. Normal landing ensued at our departure airport. Maintenance inspected aircraft for approximately 50 minutes and initially said the window had to be replaced. After additional inspection Maintenance returned aircraft to service noting the area was just within limits. Flight continued to our destination normally. Suggest LOFT training for pilot group utilizing manual vertical speed control for a leg. The system is a little fussy in manual and the design is unusual in that one can't set a target cabin altitude.

Data retrieved from NASA's ASRS site as of April 2012 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.