Date: 201308
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Dusk
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Air Conditioning and Pressurization Pack
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Human factors: Human-Machine Interface; Situational Awareness; Time Pressure
Anomaly: Aircraft Equipment Problem Critical
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Returned To Departure Airport; General Declared Emergency
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During cruise flight at FL 350 and approximately 45 minutes into the flight the advisory EICAS message PACK 2 VLV CLOSE appeared. The Captain handed me the QRH and instructed me to find the appropriate procedure for the message. Less than 1 minute later (before I could even begin reading from the QRH) the PACK 1-2 VLV CLOSE message appeared and as I was going to begin reading from the QRH the Captain stated we needed to descend to 10;000 FT after noticing the cabin altitude increasing. I informed ATC as the Captain began performing an emergency descent and shortly after (as the cabin altitude increased) the Captain; ACM and I donned our oxygen masks. ATC then cleared us to descend to 10;000 FT. During the descent ATC asked for the reason for the descent and I answered 'loss of pressurization.' Also during the descent the Captain informed the Flight Attendant of the descent and loss of pressurization; confirmed that the cabin oxygen masks had dropped and asked if there were any passenger issues/injuries. The Flight Attendant confirmed there were none. Shortly after beginning our descent the EICAS message AUTO PRESS FAIL was presented. The cabin altitude reached a maximum of at least 16;000 - 18;000 FT. After leveling at 10;000 FT and stowing our masks (returning to headset use) ATC asked our intentions. I informed ATC that we would stay on course for the time being but would most likely be return to our departure airport. After a discussion involving me the Captain and the ACM and with approval from the Dispatcher I informed ATC we would be returning to our departure airport. The Captain gave me the aircraft as he confirmed fuel status; amended the flight plan; made a PA; and communicated with Dispatch via ACARS. The remainder of the return flight was flown at 10;000 FT. The heat in the airplane became excessive; so for comfort and passenger considerations we attempted to and were able to successfully reset pack 2 then later pack 1. I recall the maximum temp in the cockpit was 36 Celsius before resetting pack 1. During this time the auto pressurization control showed an error message and we adjusted cabin altitude per the QRH manually.Due to changes in thrust during descent and approach and in inability to have exact control over cabin altitude the cabin altitude was approximately 100 feet below field elevation during landing.In my opinion the crew responded correctly and in a timely manner. The emergency descent was performed safely and no limitations were exceeded. I am unclear why the pack valves closed. There were no indications of a pack overload or overheat nor an indication of a bleed issue. The packs; bleeds and crossbleed were in their normal cruise configuration. After a short discussion with a member of Maintenance on the ground I am no closer to knowing what caused the pack valve closures. I am not sure what could have been done to prevent this. Perhaps had there been time the run the QRH procedure for the initial EICAS message the pack may have reset and the loss of pressurization averted.




Synopsis: An ERJ-145 flight crew initiated an emergency descent; declared an emergency with ATC and; ulimately; returned to their departure airport following the loss of both air conditioning and pressurization packs.