Narrative:

Emergency divert and landing. During cruise flight; at FL370; the first officer's windscreen seal failed. A loud hiss and whistle developed. It went from silent to loud instantaneously. We immediately and simultaneously did a number of things. Both of us put our crotch straps and shoulder harnesses on; we pulled out our oxygen masks; turned on the seatbelt sign and made a quick PA announcement; told ATC we needed to descend to FL250 (so as to lessen the differential pressure on the windscreen) and started discussing our options. The first officer was the pilot flying; so I kept him flying and additionally gave him ATC radio responsibilities while I contacted dispatch and maintenance. ATC was informed as to the reason we needed to descend; that it wasn't an emergency; and that the cabin was not losing pressure. They stepped us down as quickly as traffic would allow. Initially; I was able to explain the situation to dispatch that we had a leak but the cabin pressure was holding nicely and that the plan was to descend to FL250 for the rest of the flight but; as maintenance was brought onto the line; we lost radio contact. I tried both frequencies listed in the fom for our area and did not get any contact with radio for the next 10-15 minutes. In the meantime; during the descent; the whistling went away for about 1 minute. Then it came back louder. At some point below about FL270; it went away again. Differential pressure at FL370 was 8.0 psi. We wanted it at 7.0 psi or less. It took going down to FL190 for that to happen. We stayed in 'automatic' on the pressurization instead of 'manual' because the cabin pressure was rock solid and the 'automatic' system was working fine. Yes; we could have decreased the pressure on the window further by using the 'manual' method; but we were satisfied with the way the computer was handling it; and our workload was quite heavy already. ZZZ was rapidly approaching. With NORDO contact with dispatch; I was leaning further that direction. We set up the FMC for a ZZZ arrival on the secondary flight plan page; got the ATIS; and discussed our options. We decided that unless we get information from maintenance and dispatch to do something different very soon; we have to go there. We were very busy. When we had the line-of-sight with ZZZ; we got comrdo back. Dispatch said he was having trouble getting maintenance on the line; so I just called 'uncle!' I told him we were diverting into ZZZ and would let maintenance fix it there unless he disagreed with me. He didn't. The descent from FL370 wasn't overly expeditious nor was there a lot of leveling off. We were close enough to ZZZ when this started that we were luckily on what turned out to be a fairly normal descent profile for landing there. We coordinated with the flight attendants; told them the abbreviated story; didn't ask for a cabin preparation or advisory; then told the passengers about diverting and why. We declared an emergency as a precaution; landed; and taxied to the gate with no further problems -- at least on this jet; but that's another report.

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Original NASA ASRS Text

Title: A319 First Officer windscreen seal failed at FL370; fight crew requested lower and after failed radio communications with Dispatch and Maintenance decided a divert was their best situation. Emergency was declared followed by an uneventful landing.

Narrative: Emergency divert and landing. During cruise flight; at FL370; the First Officer's windscreen seal failed. A loud hiss and whistle developed. It went from silent to loud instantaneously. We immediately and simultaneously did a number of things. Both of us put our crotch straps and shoulder harnesses on; we pulled out our oxygen masks; turned on the seatbelt sign and made a quick PA announcement; told ATC we needed to descend to FL250 (so as to lessen the differential pressure on the windscreen) and started discussing our options. The First Officer was the Pilot Flying; so I kept him flying and additionally gave him ATC radio responsibilities while I contacted Dispatch and Maintenance. ATC was informed as to the reason we needed to descend; that it wasn't an emergency; and that the cabin was NOT losing pressure. They stepped us down as quickly as traffic would allow. Initially; I was able to explain the situation to Dispatch that we had a leak but the cabin pressure was holding nicely and that the plan was to descend to FL250 for the rest of the flight but; as Maintenance was brought onto the line; we lost radio contact. I tried both frequencies listed in the FOM for our area and did not get ANY contact with radio for the next 10-15 minutes. In the meantime; during the descent; the whistling went away for about 1 minute. Then it came back louder. At some point below about FL270; it went away again. Differential pressure at FL370 was 8.0 PSI. We wanted it at 7.0 PSI or less. It took going down to FL190 for that to happen. We stayed in 'automatic' on the pressurization instead of 'manual' because the cabin pressure was rock solid and the 'automatic' system was working fine. Yes; we could have decreased the pressure on the window further by using the 'manual' method; but we were satisfied with the way the computer was handling it; and our workload was quite heavy already. ZZZ was rapidly approaching. With NORDO contact with Dispatch; I was leaning further that direction. We set up the FMC for a ZZZ arrival on the secondary flight plan page; got the ATIS; and discussed our options. We decided that unless we get information from Maintenance and Dispatch to do something different very soon; we have to go there. We were very busy. When we had the line-of-sight with ZZZ; we got COMRDO back. Dispatch said he was having trouble getting Maintenance on the line; so I just called 'Uncle!' I told him we were diverting into ZZZ and would let Maintenance fix it there unless he disagreed with me. He didn't. The descent from FL370 wasn't overly expeditious nor was there a lot of leveling off. We were close enough to ZZZ when this started that we were luckily on what turned out to be a fairly normal descent profile for landing there. We coordinated with the Flight Attendants; told them the abbreviated story; didn't ask for a cabin preparation or advisory; then told the passengers about diverting and why. We declared an emergency as a precaution; landed; and taxied to the gate with no further problems -- at least on this jet; but that's another report.

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.