EMB ERJ 145 ER/LR
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; General Declared Emergency
Aircraft
We departed uneventfully and leveled off at FL240. We heard the master warning and saw the cabin altitude in the red box showing 10;000 feet and climbing. We ran the AUTO PRSN QRH and noticed the Cabin Altitude still rising. The Captain declared an emergency and after notifying ATC we descended down to 10;000 feet. As the Cabin Altitude was increasing [I] and the Captain donned our oxygen masks. The cabin oxygen masks deployed for the passengers. We were eventually via manual control (pressurization) able to bring down the Cabin Altitude. We returned to [departure airport] and landed uneventfully. We were however 400 lbs over our structural landing weight. After landing we were met by the ARFF and we let them know we were okay to taxi to the gate. Take time when running the QRH. Be methodical and efficient.
EMB-145XR F/O reported after departure cabin began to depressurize at FL240. Crew ran the QRH; declared an emergency; and returned to departure airport.