MD-82
Flight Crew Air Transport Pilot (ATP)
Distraction; Time Pressure; Training / Qualification; Troubleshooting; Workload; Situational Awareness
Aircraft Equipment Problem Critical; Inflight Event / Encounter Weather / Turbulence
Flight Crew Overcame Equipment Problem; Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory; General Declared Emergency
Weather; Aircraft
While flying level cruise at FL330 with engine and airfoil ice protection on and established for 20 minutes; low flow light on annunciation came on indicating a climbing cabin pressure. Both pack flow indications indicated zero with a cabin pressure rising at 700 FPM. Immediately started descent to lower altitude while running appropriate checklist. With anti-ice all turned off; regained both packs and had pressurization once again at FL250. As still in icing conditions in and out of the clouds; turned back on ice protection and cross feeds. Two minutes later lost pressurization a second time with both packs shutting down. Declared an emergency this time and descended as rapidly as possible to 10;000 FT MSL. Cabin never got above 9;200 FT and warning nor did passenger oxygen masks ever deploy. As normal pressurization returned at 10;000 FT; continued 240 miles to destination with sufficient fuel for normal landing at our filed destination.
At approximately 26;000 FT; packs registered air flow; and at some point during the descent the Captain turned off the anti-ice. Leveled off at 25;000 FT but needed anti-ice system. With the anti-ice system on we lost both packs; again and coordinated with ATC to descend to 10;000 FT. During the descent with the anti- ice off both packs came back online and the pressurization system functioned normally.
Both MD-82 Packs shutdown at FL330 with engine and airfoil anti-ice ON so a descent was begun immediately. The packs recovered temporarily at FL250. After a second dual pack shutdown; an emergency was declared and the flight continued at 10;000 FT.