|37000 Feet||Browse and search NASA's
Aviation Safety Reporting System
|Local Time Of Day||1801 To 2400|
|Locale Reference||navaid : lal.vortac|
|Altitude||msl single value : 34000|
|Controlling Facilities||artcc : zjx.artcc|
tower : clt.tower
|Operator||common carrier : air carrier|
|Make Model Name||B757-200|
|Operating Under FAR Part||Part 121|
|Flight Phase||climbout : intermediate altitude|
|Affiliation||company : air carrier|
|Function||flight crew : captain|
oversight : pic
|Experience||flight time last 90 days : 90|
flight time total : 14000
flight time type : 90
|Affiliation||company : air carrier|
|Function||flight crew : first officer|
|Experience||flight time last 90 days : 9|
flight time total : 162
flight time type : 9
|Anomaly||aircraft equipment problem : critical|
|Independent Detector||aircraft equipment other aircraft equipment : cabin alt warning|
|Resolutory Action||flight crew : overcame equipment problem|
Flight Crew Human Performance
We were climbing out of about FL340 to a filed altitude of FL390. The first officer was flying and the autoplt was engaged. The cabin altitude alert illuminated along with the audio warning. We confirmed that the cabin altitude had exceeded 10000 ft MSL and was still climbing. We donned oxygen masks and advised ATC that we had a pressurization problem and would have to descend until we could get the cabin below 10000 ft. ATC gave us a vector off course and an initial descent to about FL230. Shortly after that we were given clearance to descend to 11000 ft. At this point; we had run the recall items and gone to the cabin altitude checklist in the QRH. The outflow valve was already fully closed. Shortly after the cabin altitude warning and during our descent; we got pressurization 'automatic 1' and 'automatic 2' messages. As is common practice; after departure we had turned off the left pack to reduce cockpit noise. While we were descending to 11000 ft and running the checklists; I noticed that the right engine bleed valve was off; although the bleed switch was on. I now realized that we had lost pressurization because neither pack was pressurizing the aircraft. I turned the left pack on and the aircraft began to pressurize; but the automatic pressure controllers were still inoperative. During the descent we established contact with dispatch and maintenance. I described the problem and advised maintenance that we were within 100 mi of pie; mco and jax. By this time; we had gotten the cabin down to 8000 ft and were able to remove our oxygen masks. Also about this time; while I was discussing the problem with maintenance; the right engine bleed valve began to function. No corrective action had been taken on our part. We now had 2 bleed sources and 2 packs. Shortly after this happened we got the pressurization automatic controllers back. I advised maintenance of all these events and they asked us to proceed to destination. We climbed to FL320 and proceeded to destination uneventfully. The duct pressure; with the isolation valve closed; was high at climb and cruise power on both sides of the manifold; over 60 psi. The noise level in the cockpit (dual or single pack operation) was also higher than usual. The maintenance discrepancies were written up with clarifying notes and a contract mechanic met the aircraft. We assisted him with an engine run to perform the required maintenance procedures and maintenance authority/authorized the mechanic to clear the logbook entries. When the left pack had been initially turned off after takeoff I had cleared the EICAS messages for the left pack and the left engine bleed 'off.' when operating in this mode it is not uncommon for the 'bleed off' message to reappear. I suspect that this had happened and I did not clear the 'bleed off' message in a timely manner. We had also been using center tank fuel and then balancing the wing fuel and the fuel pump messages had been intentionally left on the screen as a reminder. Accordingly; when the right bleed valve failed; neither of us noticed that another EICAS message had appeared until we got the cabin altitude warning. Interestingly; the recirculation fan appeared to keep the cabin temperature comfortable during the event and the cockpit noise level did not drop enough for us to notice the problem prior to the warning. Callback conversation with reporter revealed the following information: reporter stated that it is company practice to operate with 1 pack -- both packs only required during takeoff. Apparently aircraft ducting on company's B757's creates a noise level that can interfere with communications unless one pack (normally the left) is turned off.
Original NASA ASRS Text
Title: B757 CABIN ALT EXCEEDS 10000 FT WHILE CLIMBING THROUGH FL340 ON ONE PACK. CARGO FLT CREW OBTAINS ATC CLRNC TO DESCEND FOR TROUBLESHOOTING; AND REGAINS PRESSURIZATION.
Narrative: WE WERE CLBING OUT OF ABOUT FL340 TO A FILED ALT OF FL390. THE FO WAS FLYING AND THE AUTOPLT WAS ENGAGED. THE CABIN ALT ALERT ILLUMINATED ALONG WITH THE AUDIO WARNING. WE CONFIRMED THAT THE CABIN ALT HAD EXCEEDED 10000 FT MSL AND WAS STILL CLBING. WE DONNED OXYGEN MASKS AND ADVISED ATC THAT WE HAD A PRESSURIZATION PROB AND WOULD HAVE TO DSND UNTIL WE COULD GET THE CABIN BELOW 10000 FT. ATC GAVE US A VECTOR OFF COURSE AND AN INITIAL DSCNT TO ABOUT FL230. SHORTLY AFTER THAT WE WERE GIVEN CLRNC TO DSND TO 11000 FT. AT THIS POINT; WE HAD RUN THE RECALL ITEMS AND GONE TO THE CABIN ALT CHKLIST IN THE QRH. THE OUTFLOW VALVE WAS ALREADY FULLY CLOSED. SHORTLY AFTER THE CABIN ALT WARNING AND DURING OUR DSCNT; WE GOT PRESSURIZATION 'AUTO 1' AND 'AUTO 2' MESSAGES. AS IS COMMON PRACTICE; AFTER DEP WE HAD TURNED OFF THE L PACK TO REDUCE COCKPIT NOISE. WHILE WE WERE DSNDING TO 11000 FT AND RUNNING THE CHKLISTS; I NOTICED THAT THE R ENG BLEED VALVE WAS OFF; ALTHOUGH THE BLEED SWITCH WAS ON. I NOW REALIZED THAT WE HAD LOST PRESSURIZATION BECAUSE NEITHER PACK WAS PRESSURIZING THE ACFT. I TURNED THE L PACK ON AND THE ACFT BEGAN TO PRESSURIZE; BUT THE AUTO PRESSURE CTLRS WERE STILL INOP. DURING THE DSCNT WE ESTABLISHED CONTACT WITH DISPATCH AND MAINT. I DESCRIBED THE PROB AND ADVISED MAINT THAT WE WERE WITHIN 100 MI OF PIE; MCO AND JAX. BY THIS TIME; WE HAD GOTTEN THE CABIN DOWN TO 8000 FT AND WERE ABLE TO REMOVE OUR OXYGEN MASKS. ALSO ABOUT THIS TIME; WHILE I WAS DISCUSSING THE PROB WITH MAINT; THE R ENG BLEED VALVE BEGAN TO FUNCTION. NO CORRECTIVE ACTION HAD BEEN TAKEN ON OUR PART. WE NOW HAD 2 BLEED SOURCES AND 2 PACKS. SHORTLY AFTER THIS HAPPENED WE GOT THE PRESSURIZATION AUTO CTLRS BACK. I ADVISED MAINT OF ALL THESE EVENTS AND THEY ASKED US TO PROCEED TO DEST. WE CLBED TO FL320 AND PROCEEDED TO DEST UNEVENTFULLY. THE DUCT PRESSURE; WITH THE ISOLATION VALVE CLOSED; WAS HIGH AT CLB AND CRUISE PWR ON BOTH SIDES OF THE MANIFOLD; OVER 60 PSI. THE NOISE LEVEL IN THE COCKPIT (DUAL OR SINGLE PACK OP) WAS ALSO HIGHER THAN USUAL. THE MAINT DISCREPANCIES WERE WRITTEN UP WITH CLARIFYING NOTES AND A CONTRACT MECH MET THE ACFT. WE ASSISTED HIM WITH AN ENG RUN TO PERFORM THE REQUIRED MAINT PROCS AND MAINT AUTH THE MECH TO CLR THE LOGBOOK ENTRIES. WHEN THE L PACK HAD BEEN INITIALLY TURNED OFF AFTER TKOF I HAD CLRED THE EICAS MESSAGES FOR THE L PACK AND THE L ENG BLEED 'OFF.' WHEN OPERATING IN THIS MODE IT IS NOT UNCOMMON FOR THE 'BLEED OFF' MESSAGE TO REAPPEAR. I SUSPECT THAT THIS HAD HAPPENED AND I DID NOT CLR THE 'BLEED OFF' MESSAGE IN A TIMELY MANNER. WE HAD ALSO BEEN USING CTR TANK FUEL AND THEN BALANCING THE WING FUEL AND THE FUEL PUMP MESSAGES HAD BEEN INTENTIONALLY LEFT ON THE SCREEN AS A REMINDER. ACCORDINGLY; WHEN THE R BLEED VALVE FAILED; NEITHER OF US NOTICED THAT ANOTHER EICAS MESSAGE HAD APPEARED UNTIL WE GOT THE CABIN ALT WARNING. INTERESTINGLY; THE RECIRCULATION FAN APPEARED TO KEEP THE CABIN TEMP COMFORTABLE DURING THE EVENT AND THE COCKPIT NOISE LEVEL DID NOT DROP ENOUGH FOR US TO NOTICE THE PROB PRIOR TO THE WARNING. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT IT IS COMPANY PRACTICE TO OPERATE WITH 1 PACK -- BOTH PACKS ONLY REQUIRED DURING TKOF. APPARENTLY ACFT DUCTING ON COMPANY'S B757'S CREATES A NOISE LEVEL THAT CAN INTERFERE WITH COMMUNICATIONS UNLESS ONE PACK (NORMALLY THE LEFT) IS TURNED OFF.
Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.