Date: 201309
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Night
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
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: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Physiological - Other; Time Pressure; Training / Qualification; Fatigue; Distraction; Human-Machine Interface
Second reporter function: Captain; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action; General Declared Emergency
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: The airplane was received with PACK 1 MEL'd. During the preflight briefing; the Captain reviewed the associated MEL limitations with the First Officer including the expected presence of the message PACK 1 VLV CLSD on the EICAS. During cruise at FL250; the warning message CABIN ALT appeared on the EICAS along with an advisory message PACK 1-2 VLV CLSD. An aural 'Cabin; Cabin' was heard. The cabin pressure indicator flashed 12;500 FT in red. The Captain; who was pilot flying; initiated the immediate memory items for an emergency descent; followed by a verbal review of the Emergency Checklist by the First Officer. A descent was initiated to 10;000 FT; and an emergency was declared to ATC by the First Officer. ATC cleared the aircraft to 9;000 FT. Upon reaching 9;000 FT; the airplane was reconfigured to cruise configuration; and an assessment was made by the crew of the scenario. The warning message had disappeared from the EICAS and the cabin pressure indicator was no longer in red. The QRH was referenced for the PACK 1(2) VLV CLSD message that still appeared on the screen. The aircraft was reconfigured into the clean configuration using the After Takeoff and Cruise checklists. At that time; the event was discussed by the crew and a decision was made to continue to the destination given that adequate fuel was on board; no weather threats were reported; and no other issues concerned the safety of the flight.The flight was the last of a long five leg day. The crew was tired; and ready to get to the overnight. It was dark. The crew had not eaten a meal [in about ten hours]. The airplane already had an MEL present for an inoperative PACK 1. The message associated was present on the screen as PACK 1 VLV CLSD. When the 2nd valve closed; the message remained an advisory on the screen; but now had the subtle difference of being PACK 1-2 VLV CLSD. This change was missed by the crew. Had scans been better; and had this slight change been detected; the emergency descent could have been prevented. During the event; there was an initial moment of shock and confusion as to what was happening. The events practiced in training were not smoothly initiated as if it were a training event. While all of the proper steps; I believe; were taken; the verbal communication was stifled as each person attempted to grasp what was happening. For example; the initial memory items were not completed perfectly; but the Captain called for the checklist to confirm all items were completed. I feel as if it took me longer to assess the situation than it should have. I felt slightly behind the aircraft at the event occurred; and my immediate reaction was the grab the checklist as opposed to thinking about the memory items. I suspect a more notable reminder that the 'possibility' of a pressurization problem exists when only using one pack could have better prepared the crew for the event. The change in the message from PACK 1 VLV CLSD to PACK1-2 VLV CLSD could/should have been caught earlier given a second indication; or a ding. It is too subtle a change to catch late at night on the 5th leg of a 5 leg day. I could review my Emergency checklist with more regularity. I had not thought through the Emergency Descent Checklist in probably a month. After further consideration; I believe we should have performed the Rapid Cabin Depressurization checklist upon seeing the cabin altitude turn red; and then followed it with the emergency descent. This would have ensured the crew adequate oxygen in the event we could not get the airplane down to a lower altitude fast enough. In hindsight; I this would have been a correct step.


Second narrative: We reset PACK #2 and the aircraft began pressurizing again. We ascertained that either PACK #2 shutdown during cruise flight and we did not notice the annunciation on the EICAS; or PACK #2 shut down during the emergency descent; and there was another unknown cause of the depressurization. At this point; we discerned that the cabin was holding pressure; but we would stay at 10;000 MSL as a precaution. We had enough fuel to arrive at our destination safely so we continued on to our destination.Threats: Last leg of 5 legs; long duty day (we were on our 13 hour of duty); we hadn't had time to eat yet. Errors: Not noticing a possible EICAS message earlier in the flight that may have prevented an emergency descent. In learning from this event; I realized how important it is to monitor the EICAS and understand the possible dangers of operating on only [one] PACK.


Synopsis: An EMB-145 was dispatched with PACK 1 MEL'ed and an EICAS advisory message PACK 1 VALVE CLSD. When PACK 2 failed the message was PACK 1-2 VALVE CLSD but the crew missed the subtle change so when the CABIN; CABIN aural alert sounded as the cabin climbed; an emergency was declared and the flight descended safely.