Narrative:

Upon accepting the aircraft noted that one air conditioning pack was deferred. We were delayed several hours due to thunderstorms in the area. After takeoff the pilot flying mentioned the aircraft wanted to pull very hard to the left. Followed the departure procedure and needed to deviate due to the storms. While working the radar and deviating the after takeoff check was called for. I the pilot not flying switched the bleeds to the engines and the good pack then over pressurized. Followed the emergency checklist the pack did not come back on line; leaving the cabin unpressurized. Climbing out of 7;000 or so feet the pilot flying started saying she was feeling hypoxic and we needed to get down. I looked at the altimeter and noticed we were below 10;000 and due to the high work load really couldn't figure out why she was becoming hypoxic. She was very adamant about returning back. She was working the radios because I was still dealing with the pack. I got the pack on the line and said are you okay to continue she said no we have to land. So we proceeded back. The reason why this happened is because I; as the pilot not flying; did not follow the proper procedure in the single pack operation which led to the aircraft not immediately pressurizing. Once I got the pack on line and we were still below 10;000 the pilot flying had symptoms of hypoxia and we needed to land. This all was happening with lots of thunderstorms in the area and dealing with the areas congested airspace. Due to the high work load of the situation I needed to slow down and follow the procedure in the QRH for a single pack operation. I should have briefed it better on what was going to happen when we switched the bleeds from the APU to the engines.

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Original NASA ASRS Text

Title: A CRJ200 Captain; the non-flying pilot; switched the bleed to the engine and the single operating pack over pressurized. Following the emergency procedure the pack was returned but the First Officer reported hypoxic symptoms even though the cabin altitude did not exceed 10;000 FT.

Narrative: Upon accepting the aircraft noted that one air conditioning pack was deferred. We were delayed several hours due to thunderstorms in the area. After takeoff the pilot flying mentioned the aircraft wanted to pull very hard to the left. Followed the departure procedure and needed to deviate due to the storms. While working the radar and deviating the after takeoff check was called for. I the pilot not flying switched the bleeds to the engines and the good pack then over pressurized. Followed the emergency checklist the pack did not come back on line; leaving the cabin unpressurized. Climbing out of 7;000 or so feet the pilot flying started saying she was feeling hypoxic and we needed to get down. I looked at the altimeter and noticed we were below 10;000 and due to the high work load really couldn't figure out why she was becoming hypoxic. She was very adamant about returning back. She was working the radios because I was still dealing with the pack. I got the pack on the line and said are you okay to continue she said no we have to land. So we proceeded back. The reason why this happened is because I; as the pilot not flying; did not follow the proper procedure in the single pack operation which led to the aircraft not immediately pressurizing. Once I got the pack on line and we were still below 10;000 the pilot flying had symptoms of hypoxia and we needed to land. This all was happening with lots of thunderstorms in the area and dealing with the areas congested airspace. Due to the high work load of the situation I needed to slow down and follow the procedure in the QRH for a single pack operation. I should have briefed it better on what was going to happen when we switched the bleeds from the APU to the engines.

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.