Date: 201209
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: Thunderstorm; Turbulence
Light: Dusk
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Air Conditioning and Pressurization Pack
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action
Contributing factors: Human Factors; Aircraft; Weather
Primary problem: Aircraft

Narrative: We were cruising at FL360 and noted the presence of thunderstorm activity about 50 NM ahead of us and asked ATC for a deviation to the right (west) to go around it. They told us that the very tall cumulus nimbus was at our 12 o'clock but if we took a 10-15 degree turn to the west we could miss that very tall cell and we would be able to clear the lower weather to the west of the cumulus nimbus. We took a 10 degree turn to a heading of approximately 220 degrees. Whilst on top of the weather; both the First Officer and I noticed the pressure beginning to build in our ears. We saw that the cabin altitude had climbed to about 9;000 FT and was continuing to climb somewhat rapidly. I also noticed that both packs had cyan failure messages. I attempted to recycle both packs off and then on; to no effect. By this time the cabin altitude was around 9;700 or so and still climbing rapidly. I called the flight attendant who was toward the back of the aircraft and told her to sit down immediately; which she did. I then told ATC that we required an immediate descent to FL180. They told us that we were cleared to FL180 and asked if we needed any assistance. I told them we had lost both pressurization packs and needed to descend very quickly. I did not declare an emergency; as I didn't feel it was necessary to do so. We completed an emergency descent at about 5;000 FPM. As we began our descent I revised my requested altitude to 10;000 FT which ATC approved. The emergency descent took us right in to the weather. There was no lightning present; because we had passed to the west of the worst part of the storm system. There was; however; continuous moderate turbulence throughout our descent. I realized we were heading further into the cell and requested a right turn to the northwest from ATC to get back out of the weather. We were given a turn to approximately 320 degrees. I had considered the donning of our crew O2 masks; but I paid close attention to the cabin altitude; and after rising to about 12;000 FT it began descending again. This told me that at least one of the packs had begun working again. I decided against putting our O2 masks on. The cabin altitude continued to descend as we descended to 10;000 FT. Once we were below 14;000 FT I told my First Officer to slow our rate of descent; which he did. During the descent; I believe through about FL180; I advised ATC that we were requesting a diversion to a nearby airport for landing; as there was no way we could continue on to destination with the fuel remaining (approximately 6;700 LBS) at 10;000 FT. Once level at 10;000 FT we had to fly around 10 NM or so further to the northwest until we got out of the moderate turbulence. At that time; I started to prepare for a landing in the nearest airport. Complicating the issue was the fact that our ACARS was on MEL and so I had no quick way of contacting Dispatch. Once we had completed our emergency descent to 10;000 I considered using Commercial Radio to contact the Dispatcher to advise them of our diversion but we were still in the inclement weather and I decided to exercise my Captain's Emergency Authority to just divert ourselves; and I would contact Dispatch and Maintenance Control once we were safely on the ground at the airport. We were under our landing structural weight for landing in the airport; so there was no issue with that. We were handed off to the TRACON as we made our way toward the airport. We asked for and were given delay vectors so we could build and brief the approach; as well as brief the passengers and the Flight Attendant on the situation. I tried for 15 minutes to contact Operations while airborne to no avail. We also had the TRACON and Tower try to call them on the phone but they didn't answer. We landed without incident and taxied to the holding pad while we again tried for 10 minutes to call operations. Finally they answered us and gave us a gate; to which we taxied; parked and deplaned the passengers. Once safely at the gate and with the passengers deplaned; I called Dispatch and advised them that we had deviated to the nearest airport and told them what had happened. I told them I would call Maintenance Control to try to see what had gone wrong with the packs and then I would get back to them. I called Maintenance; explained that we had had a dual pack failure at FL360 and had made an emergency descent and diverted to the nearest airport. After asking me a few questions about the event he had me turn on the APU and run the packs; both of which worked on the ground. He then had me pull up the maintenance page on the MFD to see if there had been any system errors logged by the aircraft. There were three error messages associated with our incident. I told him what they were and he said that they would need to fix the plane. We were aircraft swapped to another aircraft; which arrived around four hours later. We departed and continued on to destination without further incident.The lack of ACARS; made it difficult to easily contact Dispatch to advise them of our diversion to an unlisted alternate. The inclement weather made our emergency descent uncomfortable and challenging. The pack malfunction caused the incident. In retrospect; I might have reconsidered my non-declaration of an emergency; if only to have expedited and priority handling from ATC.




Synopsis: EMB145 Captain experiences a dual pack failure at FL360 and diverts to a suitable alternate after an emergency descent with ATC approval; but without an official declaration of an emergency. The descent is through weather and moderate turbulence is encountered and the cabin altitude reaches 12;000 FT. The crew elects not to use their oxygen masks during the event.