B737 Undifferentiated or Other Model
Air Traffic Control Fully Certified
ATC Issue All Types; Aircraft Equipment Problem Critical; Airspace Violation All Types
General Declared Emergency
Aircraft; Human Factors; Procedure
I was working the RADAR at Multiple Sectors due to low traffic and low complexity. There was no D-Side for the same reasons. Below our sectors are Approach Control's with a shelf splitting the two. A B737 was en route at FL350. The B737 was PVD'd onto my screen from Sector 38. Sector 38 called and reported that the B737 had a rapid pressure loss and was descending at an accelerated rate. I accepted RADAR contact with the B737 descending rapidly. I called to coordinate a point out to Approach and future handoff; with the code and that the aircraft was an emergency and would be entering their airspace descending rapidly. I asked the B737 to report altitude; 120 was reported. I then called and asked approach for lower to 080. An altitude was never available from HOST on the aircraft. The aircraft may have entered Approach's airspace during coordination; however I could not tell as no altitude was shown in the data block due to the rapid descent. I observed no aircraft in TRACON's airspace during the event. The plane leveled and reported at 080 and Approach accepted a handoff. I attempted to find the pilot's intentions but was asked to stand by. I transferred communications and the plane landed.
We departed without incident. Just prior to leveling off at our planned cruise altitude; the Equipment Cooling Off light illuminated. As per the QRH; the alternate switch position was selected. However; other than a minor change in gen. amps; there was no change to the light indication. The flight was also continued as per QRH. After a discussion of possible trouble shooting circuit breakers etc; we sent Maintenance Control an ACARS message indicating the condition and to have it addressed upon arrival. We were met at the gate by Contract Maintenance and I discussed the issue with both Dispatch and Maintenance Control. The Contract Mechanic entered the E&E compartment and subsequently rectified the problem. The logbook was reviewed and signed off. The aircraft was boarded and departed to our destination on time with no further complications. Our initial climb through 10;000 FT was normal and our Climb Checklist indicated all systems functioning. Shortly afterward; the Master Caution illuminated indicating that the Equipment Cooling Off light was illuminated on. The QRH was once again consulted and we proceeded as directed. I instructed the pilot not flying to send Maintenance Control another ACARS message to have Maintenance meet the aircraft to rectify the situation. Passing approximately FL270 for FL340; the intermittent warning horn sounded. I immediately observed that the cabin altitude was indicating approximately 10;000 FT and a positive rate of climb (500-700 FPM). I instantly observed/confirmed the pressurization panel for proper switch configuration. I announced we initiated our Cabin Altitude Warning/Abnormal Pressurization procedures and memory items. Without delay; both pilots donned our oxygen masks and established communication. I instructed the pilot not flying to consult the checklist and prepare for an emergency descent. While he was reading/confirming our memory items; I agreed that we proceed to attempt to operate the outflow valve in manual. I continued to assess the situation and noted that we had no abnormal ear discomfort or noise indicative of a rapid depressurization; however; calculating the rate of cabin climb (even though we advised ATC and a 'leveled-off') it would only take four to five minutes for the cabin to reach 14;000 FT. I asked the pilot not flying if he was having any effect with the outflow valve and he initially indicated none. We agreed to now execute an emergency descent which was accomplished per QRH. As per procedure; I calmly advised the flight attendants by interphone and passengers by P/A.During our descent the pilot not flying indicated that he was starting to see a reversal in the cabin climb rate. I mainly focused on the aircraft control and traffic etc. as we were given headings and clearances from ATC. I once again summoned the flight attendants on the intercom to evaluate the cabin environment and they reiterated that everyone was seated and secure and that no mask had yet dropped. Upon discussion with the pilot not flying and ATC; it was decided to land due to its close proximity and runway availability etc. We then leveled off at 10;000 FT briefly and proceeded to prepare for landing; an 'overweight landing' was noted (113;000 LBS) but not runway distance limiting. I asked the pilot not flying to try to contact Dispatch time permitting! After a smooth landing; we taxied to the gate. On taxi in we noted that there was a 'shrill' noise coming from the cabin. Upon arrival at the gate; I noticed that we were still slightly pressurized and pointed out that the pilot not flying needed to fully open the outflow valve. I instructed the flight attendants to not attempt to open the doors until instructed and left the seat belt sign on. Shortly after; we accomplished depressurization and the flight attendants opened the doors. Upon opening the cockpit door; the flight attendant indicated that the forward lavatory fire detector was 'ringing' but there was no fire (which I confirmed). Passengers were deplaned and all were in 'good spirits.' The -700 QRH mentions that with an inoperative equipment cooling system there 'could' be a chance of an abnormal pressurization situation (not mentioned in the 300/500 QRH). There is a direct correlation through the pressure controller; forward outflow valve/pressure control valve for addition cooling at low cabin PSI; etc. I have always believed that the Cabin Altitude Warning/Abnormal Pressurization and Emergency Descent Checklists should be committed to memory if not a 'memory item' checklist. I've had one previous rapid decompression in 25 years on the 737 and they can be a very chaotic; noisy; and challenging environment.
Enroute Controller described an emergency event that resulted in an uncoordinated airspace entry event due to an emergency descent due to pressurization problems.