Date: 201210
Local time of day: 1201-1800
Location: ORD.Airport, IL
Flight conditions: IMC
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight phase: Cruise
Airspace: Class B ORD
ATC / advisory: TRACON C90
Aircraft component: Pressurization System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Human factors: Physiological - Other; Situational Awareness; Time Pressure
Anomaly: Aircraft Equipment Problem Critical
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Overcame Equipment Problem; General Declared Emergency
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: Flying at FL240 in and out of IMC with Pack 1 MEL'd. We were in the process of getting coffee from the Flight Attendant when the First Officer and I both felt a change in cabin pressure. The First Officer locked the door and we both noted the rapidly climbing cabin (it was in red in a matter of seconds). Neither of us recall the rate at which the cabin was climbing but we both agree it was very; very fast. The Flight Attendant was still on the phone since we had just closed the door and told us the masks had deployed. I told her to use the mask as well as the passengers and to be seated as we are going to descend. The First Officer and I donned our masks; notified ATC of the pressure loss and emergency descent. We squawked 7700 and I initiated the descent almost immediately since the cabin was so high and the pressure was very uncomfortable. I didn't slow to 240 KTS to wait for the gear extension prior to starting down. I just wanted to get the aircraft down since I knew the passengers were without the benefit of 100% oxygen and the cabin was lost. Midway through the descent I noticed the Pack 2 valve closed EICAS message. During the descent I called for the emergency descent QRC. It was then that I had slowed enough to drop the gear and continue the descent. During the descent we encountered ice and got the bleed low temp message since we were at idle. Once leveled off at 10;000 FT and reconfigured; Pack 2 was reset and began pressurizing again. I checked in with the Flight Attendant to make sure everyone was OK. She seemed shaken up but assured me everything was fine. I informed her that we were at 10;000 FT and oxygen was no longer necessary. We told ATC the emergency was over and everything was stable. We squawked our original beacon code. After conferring with Dispatch and Maintenance we decided the fuel load was sufficient to continue to destination at 10;000 FT. I didn't want to climb again even though the pack was working again since the oxygen generators had already been used and I didn't think the passengers wanted to experience that again if it were to happen. I feel that the aircraft cabin climbed much faster than I was ever led to believe it would if I were to loose both packs. I was taught the outflow valve would close and there would be a slow leak giving us time to get down to 10;000 FT. This event seemed more like a rapid decompression rather than a slow loss of pressurization. I would like to see the maintenance data that shows the climb rate of the cabin as well as how high it got. Also; the QRC memory items for emergency descent seem fine on the ground but in practice waiting for the aircraft to slow; drop the gear; and then begin the descent seems like a long time with a very high cabin.




Synopsis: EMB145 Captain experiences a rapid decompression at FL240 when the Number 2 pack shuts down after being dispatched with the Number 1 pack inoperative. The descent is initiated without extending the landing gear as required by the QRC. Flight continues to destination at 10;000 FT although the crew is able to reestablish pack operation.