2009-12 · NASA ASRS report 864537
After preforming a crossbleed start in a rushed atmosphere just prior to takeoff the pack switches are never turned back on. This results in a cabin altitude warning passing FL356 in the climb and an emergency descent. Passenger oxygen masks were deployed and used in the incident and flight returns to departure airport for maintenance action.
We pushed back on time. Stared the right engine; and delayed left engine start. Shut down APU as per company procedure. Taxied to Runway. During taxi ATC told us of takeoff window of XA:36 to XA:46. We started the left engine using cross bleed start procedure; and accomplished taxi checklist. After being cleared for takeoff and as the Captain advanced the thrust levers we noticed a momentary Left Engine Bleed light and associated EICAS message which cleared itself. Otherwise it was a normal takeoff. We were limited to 10;000 FT for approximately 2 minutes then eventually cleared to FL400. At approximately 35;600 FT the aural cabin altitude warning sounded with associated lights and EICAS message. As per emergency procedures the Captain had the flying duties and O2 was donned. I then checked the cabin altitude control panel and found the cabin climbing at approximately 1000 feet/min; and the cabin altitude at 10;500. I switched from Auto 1 to AUTO 2 with no control regained I then switched to MAN and tried to descend the cabin with no success. The Captain had already coordinated with ATC and initiated an emergency descent. During this time I called and asked the lead Flight Attendant if the passenger O2 masks were 'out.' She replied 'No' continuing the descent and still trying to regain control of the cabin the Captain informed ATC we would land at ZZZ. The cabin continued to climb and the lead Flight Attendant called me back to tell me the passenger O2 masks had deployed. I told her to have the passengers and crew don the O2. The cabin alt reached approximately 14 to 15;000 FT. ATC stepped us lower and vectored us for landing at ZZZ finally leveling at 7000 FT. The Captain then noticed that the pack switches were in the off position. I turned the right one on and the aircraft pressurized normally. Eventually I turned the left pack switch back on as well. We then told ZZZ Approach that we had resolved the problem and were no longer had the emergency. With the cabin pressurized normally we changed our destination back to ZZZ1. We had a normal approach and landing at ZZZ1.The company procedure for APU off and cross bleed start during single engine taxi adds complexity and task loading at a critical phase prior to takeoff. Adding to the load was a push by ATC to 'move up; next for takeoff.' Although it is a stated company procedure it's not frequently used and only the third time I recall using it. It was; therefore something I am not routinely accustomed to doing. During the procedure the Captain advances the right engine thrust to approximately 72% N1 which brought duct pressure up to approximately 32 PSI. Having the packs off; I initiated the left engine start. The spool up was unusably slow even with 32 PSI. Since we were so lightly loaded I was concerned about the Captain having to 'ride the brakes;' but still needed a bit more thrust for assist the start. The engine started normally. There was a rush to get the engine started and have a sufficient warm-up time and comply with ATC request to move up next for takeoff. Still on the taxiway; as we approached the end of the runway; I believe; but not certain we were cleared for takeoff which was changed to 'position and hold.' It came as we were trying to finish up the taxi checklist. There were multiple distractions and interruptions during the taxi checklist; and I may have missed turning the packs on after engine start. However; there were no items presented on ICAS when I called 'recall' on the taxi checklist. Because of our light weight we climbed very rapidly until the cabin altitude warning sounded. Then even after declaring an emergency we were stepped down because of traffic. It wasn't a rapid depressurization; but slow and steady; I don't recall seeing the pack lights on while I attempted to gain control of the cabin; but I was focused on the cabin altitude controller. I don't recall trying to cycle the pack switches. I suggest that the procedures be returned to the Boeing approved procedure of using the APU for normal starts. The cross bleed start should be used as a non-normal procedure only. Furthermore; if the company wants to use the cross bleed start procedure; additional training is required to determine when and how it is appropriate.
I sent an ACARS message to Dispatch that we had lost cabin pressure. Initially; they went along with a ZZZ landing. We received another message requesting that we return to ZZZ1. We requested and received a clearance to ZZZ1 at 7;000'. At this time I leveled the aircraft; changed the routing from ZZZ to ZZZ1. I looked over at the overhead panel and noticed the engine bleed switches were off. The First Officer turned the switches ON and the aircraft pressurized. We advised ATC that problem was taken care and we no longer needed emergency handling. We updated the lead Flight Attendant and passengers on our progress. The passengers reported no problems with the high cabin altitude. The crossbleed start procedures add a layer of complexity and compresses the time to accomplish the before takeoff procedures. It appears that the engine bleed switches were never turned on after the start of the left engine. I do not remember pressing the recall button after the start of the left engine. ATC gave us multiple instructions as we approached the end of the runway causing us to start and stop the checklist several times. The rapid climb of the lightweight aircraft gave us little time to analyze the problem. This was only the second time I had used the normal crossbleed start procedure after being briefed on its importance at my last training session.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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