Date: 201605
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Aircraft: MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operator: Air Carrier
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
Aircraft component: Pressurization Control System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During cruise; FL300; about 10 minutes from Top of Descent (TOD); I felt a surge in the cabin pressurization and saw the Master Caution light illuminated. Both of us began to scan items; and found that the Pressurization Flow light on the Electronic Overhead Panel (EOP) was illuminated. That was the only indication we had on the overhead that something was wrong. First Officer (FO) checked the switches and readings; and we found all in normal configuration. I asked what was the cabin doing; and I was trying to read the indications as well. I noticed that the Cabin Rate of Climb indication appeared to be full scale deflection; I asked for him to verify. He did in fact say the needle was full scale; then I asked how the cabin altitude and differential pressure readings. At that moment; they actually looked stable. There did not seem to be any change. I asked for the QRH; and as the FO was getting his book out; I could see on my own that the cabin was indeed climbing; just slowly. We modified power settings; and the pressurization flow annunciation was still illuminated. I then asked my FO to ask for a lower altitude. ATC gave us clearance to 260; and as I started my descent; and pulling back on the throttles; that only aggravated the situation; and I could see that the climb rate of the cabin intensified; I then established a rapid descent configuration and asked the FO to request lower; which he did; and I believe we were given FL170. But now with the cabin rapidly climbing; I could see we were now quickly running out of available pressure and the risk of exceeding 14K cabin altitude was now possible. The FO also noticed the climb rate; and he emphasized we needed to get down. I was flying the aircraft; and assuming we were going to exceed 14K; I commanded we put on O2 masks. As the FO was fitting his mask and establishing communications with me; I called ATC and advised them we needed a lower altitude than assigned; and that the issue was a pressurization problem. Another ATC controller then checked in and asked for SOB; nature of problem; and required assistance. The FO responded and she cleared us to 7;000 feet. I assigned; my FO; to go back to the QRH; while I fly and communicate. He did; and the manual pressurization procedure eventually was effective in controlling the cabin altitude. The maximum Cabin altitude we achieved was about 10;300 feet; and we did get the Cabin Altitude Warning for perhaps 3 seconds. Once the First Officer had the cabin back under control; I slowed descent and established a gentle descent profile; with a stable power setting; and continued on with our arrival duties. Things became much less hectic; so I was then able to communicate with the Flight Attendants and queried then on Cabin Status. They stated nothing was abnormal in the cabin or its environment; the passengers were well; with no concerns. I briefed them on what happened and our plan to continue. The First Officer suggested we had enough fuel on board and that maintenance would be an issue; so I assigned him flying and ATC duties. I contacted dispatch; briefed them on our status; and asked if [the destination] was appropriate; or would another point of landing better suit the situation. Dispatch concurred that [the destination] was best; so we proceeded with our original intentions.From that point on; it was a routine approach and landing. We wrote up the malfunction; and maintenance was there to meet us when we parked.




Synopsis: MD80 Captain reported a pressurization surge at FL300 followed by a master caution light and a flow light on the EOP. An emergency descent was initiated and manual control of the pressurization was gained prior to leveling at 10;000 feet.