MD-82
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
General Declared Emergency
Aircraft
Descending through approximately FL300 we got an aural cabin altitude warning accompanied by the master caution light and a cabin altitude indication of 10;500 feet. We accomplished the memory items for cabin altitude warning/rapid depressurization; the F/O referenced the QRH while I was flying; and we established communications with our masks on over the interphone speaker. Manual pressure control was determined to be difficult or questionable; and since we were already descending it was agreed that an emergency descent was in order. We declared an emergency with ATC; received clearance and executed an emergency descent to 8;000 feet MSL. We requested ARFF; a single frequency approach; and coordinated for vectors for a visual.I chimed the flight attendants 4 times and gave the number one Flight Attendant a 'TEST' Briefing followed by a PA where I explained to the passengers that the pressure changes that they may have felt in their ears was due to a pressurization problem and that once we were at a lower altitude our problem would be over. I reassured them that everything was under control and that there was no cause for alarm and to follow the instructions of the flight attendants. The descent was very busy. I was hand flying; the F/O was running check lists and coordinating with ATC; and we were communicating with our masks on over the interphone speaker. While in the emergency descent; the number one Flight Attendant called several times to tell us that the masks had not deployed. Priorities in the cockpit at the time did not allow investigation as to why the masks had not deployed; so I chose to manually deploy the masks to alleviate the concern in the cabin and to ensure the safety of the passengers and crew. The F/O had his hands full in the descent trying to control the pressurization manually and run the checklists. Once we were below 10;000 feet; I told him to just depressurize the aircraft. Now that the threat of hypoxia was over; I told him there was no need to rush anything and we spoke to ATC about terminating the emergency. However; when I took off my mask; I smelled a musty; smoke-like; unidentifiable odor. I put my mask back on; told the F/O to tell ATC that we were to remain an Emergency and that we wanted the fire truck to meet us upon landing. We then increased our speed to 300 knots. During the approach; I had the F/O make a PA to the passengers to advise them they would see safety vehicles and to remain seated after landing. Weather was not a factor and the approach and landing was uneventful. Upon landing; I once again told the passengers to remain seated; and after we got an okay from the fire chief; we taxied to the gate with the fire truck following us. After completing the parking checklist at the gate; I stood in the cockpit door while the passengers were deplaning and observed most of them. There were a few women that were noticeably distressed by the incident; but said nothing. An elderly gentleman complained about his ears hurting and the number one Flight Attendant directed him to the paramedics on the jet bridge. Most passengers seemed to be in good health and spirits and expressed their gratitude. I stayed on the airplane talking with Dispatch; police; Maintenance; and writing in the logbook for approximately 20 minutes after the passengers deplaned. I then went up to the gate area where the gate agents were assisting the passengers and no one there appeared to be in distress or in need of any special assistance. I stayed around the gate area for approximately 10 minutes and met some [company] pilots who spoke of possibly ferrying the aircraft; and we then went to the hotel.All in all; after being surprised by a cabin pressurization problem at altitude; the crew did a terrific job assisting me in getting the aircraft safely on the ground with no apparent injuries or damage to equipment. ATC was very helpful and I really appreciated the rapid response from the ARFF crew.
[Excerpt of pertinent information:]It was my first time reverting to and operating the manual pressurization control on this model of aircraft. It was very difficult to clearly assess the pressurization status and bring it under control. In post flight review; I now realize that our initial memory items of reverting to manual pressurization control and closing the outflow value most likely regained the cabin altitude rather quickly; so that by the time I was able to reach the point in the checklist to regain pressurization manually; the cabin altitude had already descended well below sea level (off scale). Due to the cabin pressurization gauge design; and due to the fact I was busy with procedures; I never saw the cabin descending to such a low cabin altitude. Therefore; it was difficult to know at first whether we were pressurized off scale low; or the gauge was not working with an indication of off scale high.
MD-82 began to loose cabin pressurization; executed an emergency descent and landed safely.