Narrative:

We were en route in our sabre 60. Though we have the equipment for rvsm airspace; the equipment checkout; and the pilot training; our local FSDO wanted changes to the standard rvsm submittal document provided by the stc holder; so we were limited to non-rvsm airspace -- FL280 maximum. We had just leveled at FL270 -- our cruising altitude -- and were establishing cruise when we heard and felt a loud bang or explosion in the back of the aircraft. A quick check of cabin altitude showed the cabin starting an uncommanded climb. We donned our quick-donning oxygen masks; and I pointed 'down!' the co-captain (also type rated in the sabreliner) switched to his oxygen mask microphone and advised ATC that we had an emergency depressurization and needed lower. ATC heard the 'emergency' part; but did not seem to understand the problem; requesting an explanation. The co-captain had to repeat several times -- and by that time; we had initiated descent. Because we did not know if there was damage to the aircraft; I decided not to increase speed above the speed already indicated -- 270 KTS. I deployed the speed brake. Once established in the descent; I looked at the cabin altimeter -- 5000 ft; and climbing at 4500 ft per min. Believing that the problem may be in the failure of the aft pressurized ductwork or the air cycle machine; I selected 'emergency pressurization.' this stopped the cabin depressurization; and started the cabin back down in altitude. At this time; we were able to take off our masks and communicate with the normal hand microphone. ATC advised to turn right immediately due to traffic; I complied; and continued descent. With the emergency pressurization holding cabin altitude; we asked to stop the descent at 16000 ft; ATC cleared us to 16000 ft. We ran the emergency checklist; all items had been covered from memory. We brought in power; and the aircraft handled normally; though I wasn't going to try any airspeed above 270 KTS indicated. With the application of power however; the duct overheat light came on; sensing high temperature in the ductwork. This is normal in most business jets (including the sabreliner) as engine bleed air is fed directly into the pressurization system; bypassing the air cycle machine. The designers planned for just this emergency. The proper procedure is to reduce power on the right engine to reduce the temperature in the ductwork -- extinguishing the light. We did not know the nature of the failure/damage in the aft end; but I did know that I didn't want 325 degree air in the vicinity of the aft fuel cell if it was a duct failure. After discussing the problem; we elected to descend to 10000 ft and depressurize. The 'duct hot' light went out immediately after reducing engine power. We considered landing at ZZZ; but with the large fuel load we had on board for the long trip; it would have meant either circling to burn off fuel; or an overweight landing. Since the WX was clear; we elected to bo back to our home base; 30 mins away; where we had maintenance and advisory capability. The WX was clear; and there were a number of large airports en route. All systems operated normally; the landing was uneventful. Post flight inspection revealed a failure of the aft ductwork; running in close proximity to the aft fuel tank; our analysis and actions were correct. Thinking about this post flight; we discussed the difficulty in communication. 1) oxygen mask microphones are notoriously bad; muffled. In this case; ATC had difficulty understanding our problem. 2) headsets. I'm type rated in 5 different jets. The co-captain is typed rated in 3. We fly together often. In other jets; we used light weight headsets with boom microphones. In this aircraft; the training instructor had indicated his dislike for headsets because of the difficulty in using a quick-donning mask. We elected to follow his advice; and used hand microphone and cabin speakers. During this incident; not only were we unable to communicate effectively due to the poor quality of the oxygen mask microphone; but I was unable to hear what the co-captain was telling ATC at this crucial time; or for us to communication other than by shouting; requiring removal ofthe mask. There was a lot of cockpit noise due to high indicated speed caused by the necessity to stay below rvsm airspace (indicated speeds -- and cockpit air noise -- are lower at high altitudes). In the sabreliner; there is an effective (but noisy) air brake located on the bottom of the aircraft behind the cockpit. Effective cockpit communication was hindered. I am glad we have flown together often. 3) as a result of this incident; we are making changes to our equipment and procedures. We have purchased a different style of quick-donning oxygen mask; compatible with light weight headsets. We will be using light weight headsets; so we can make use of the cockpit intercom for inter-pilot communication. 4) as a result of our own experiences in aircraft depressurization; I will use the procedure that has worked well for me; I will put the quick-donning mask on over the earpieces and microphone tube of the regular headset; rather than taking the headset off. The time spent removing the headset before donning the mask; and the poor quality of oxygen mask microphones makes this procedure preferable.callback conversation with reporter revealed the following information: the reporter stated that he attempts to mentally prepare for various scenarios that could develop while airborne. He felt that this enabled the flight crew to more efficiently deal with this emergency. He also stated that the procedure calls for reducing power on the right engine to reduce temperatures in the duct.

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Original NASA ASRS Text

Title: SABRE 60 EXPERIENCED A RAPID DEPRESSURIZATION. FLT CREW INITIATED EMER DSCNT AND DIVERTED. FLT CREW CITES COMMUNICATION ISSUES WITH QUICK-DONNING MASK INTERFERENCE WITH THEIR HEADSETS.

Narrative: WE WERE ENRTE IN OUR SABRE 60. THOUGH WE HAVE THE EQUIPMENT FOR RVSM AIRSPACE; THE EQUIPMENT CHECKOUT; AND THE PLT TRAINING; OUR LOCAL FSDO WANTED CHANGES TO THE STANDARD RVSM SUBMITTAL DOCUMENT PROVIDED BY THE STC HOLDER; SO WE WERE LIMITED TO NON-RVSM AIRSPACE -- FL280 MAX. WE HAD JUST LEVELED AT FL270 -- OUR CRUISING ALT -- AND WERE ESTABLISHING CRUISE WHEN WE HEARD AND FELT A LOUD BANG OR EXPLOSION IN THE BACK OF THE ACFT. A QUICK CHK OF CABIN ALT SHOWED THE CABIN STARTING AN UNCOMMANDED CLB. WE DONNED OUR QUICK-DONNING OXYGEN MASKS; AND I POINTED 'DOWN!' THE CO-CAPT (ALSO TYPE RATED IN THE SABRELINER) SWITCHED TO HIS OXYGEN MASK MICROPHONE AND ADVISED ATC THAT WE HAD AN EMER DEPRESSURIZATION AND NEEDED LOWER. ATC HEARD THE 'EMER' PART; BUT DID NOT SEEM TO UNDERSTAND THE PROB; REQUESTING AN EXPLANATION. THE CO-CAPT HAD TO REPEAT SEVERAL TIMES -- AND BY THAT TIME; WE HAD INITIATED DSCNT. BECAUSE WE DID NOT KNOW IF THERE WAS DAMAGE TO THE ACFT; I DECIDED NOT TO INCREASE SPEED ABOVE THE SPEED ALREADY INDICATED -- 270 KTS. I DEPLOYED THE SPEED BRAKE. ONCE ESTABLISHED IN THE DSCNT; I LOOKED AT THE CABIN ALTIMETER -- 5000 FT; AND CLBING AT 4500 FT PER MIN. BELIEVING THAT THE PROB MAY BE IN THE FAILURE OF THE AFT PRESSURIZED DUCTWORK OR THE AIR CYCLE MACHINE; I SELECTED 'EMER PRESSURIZATION.' THIS STOPPED THE CABIN DEPRESSURIZATION; AND STARTED THE CABIN BACK DOWN IN ALT. AT THIS TIME; WE WERE ABLE TO TAKE OFF OUR MASKS AND COMMUNICATE WITH THE NORMAL HAND MICROPHONE. ATC ADVISED TO TURN R IMMEDIATELY DUE TO TFC; I COMPLIED; AND CONTINUED DSCNT. WITH THE EMER PRESSURIZATION HOLDING CABIN ALT; WE ASKED TO STOP THE DSCNT AT 16000 FT; ATC CLRED US TO 16000 FT. WE RAN THE EMER CHKLIST; ALL ITEMS HAD BEEN COVERED FROM MEMORY. WE BROUGHT IN PWR; AND THE ACFT HANDLED NORMALLY; THOUGH I WASN'T GOING TO TRY ANY AIRSPEED ABOVE 270 KTS INDICATED. WITH THE APPLICATION OF PWR HOWEVER; THE DUCT OVERHEAT LIGHT CAME ON; SENSING HIGH TEMP IN THE DUCTWORK. THIS IS NORMAL IN MOST BUSINESS JETS (INCLUDING THE SABRELINER) AS ENGINE BLEED AIR IS FED DIRECTLY INTO THE PRESSURIZATION SYSTEM; BYPASSING THE AIR CYCLE MACHINE. THE DESIGNERS PLANNED FOR JUST THIS EMER. THE PROPER PROC IS TO REDUCE POWER ON THE R ENGINE TO REDUCE THE TEMP IN THE DUCTWORK -- EXTINGUISHING THE LIGHT. WE DID NOT KNOW THE NATURE OF THE FAILURE/DAMAGE IN THE AFT END; BUT I DID KNOW THAT I DIDN'T WANT 325 DEG AIR IN THE VICINITY OF THE AFT FUEL CELL IF IT WAS A DUCT FAILURE. AFTER DISCUSSING THE PROB; WE ELECTED TO DSND TO 10000 FT AND DEPRESSURIZE. THE 'DUCT HOT' LIGHT WENT OUT IMMEDIATELY AFTER REDUCING ENGINE POWER. WE CONSIDERED LNDG AT ZZZ; BUT WITH THE LARGE FUEL LOAD WE HAD ON BOARD FOR THE LONG TRIP; IT WOULD HAVE MEANT EITHER CIRCLING TO BURN OFF FUEL; OR AN OVERWEIGHT LNDG. SINCE THE WX WAS CLR; WE ELECTED TO BO BACK TO OUR HOME BASE; 30 MINS AWAY; WHERE WE HAD MAINT AND ADVISORY CAPABILITY. THE WX WAS CLR; AND THERE WERE A NUMBER OF LARGE ARPTS ENRTE. ALL SYSTEMS OPERATED NORMALLY; THE LNDG WAS UNEVENTFUL. POST FLT INSPECTION REVEALED A FAILURE OF THE AFT DUCTWORK; RUNNING IN CLOSE PROXIMITY TO THE AFT FUEL TANK; OUR ANALYSIS AND ACTIONS WERE CORRECT. THINKING ABOUT THIS POST FLT; WE DISCUSSED THE DIFFICULTY IN COMMUNICATION. 1) OXYGEN MASK MICROPHONES ARE NOTORIOUSLY BAD; MUFFLED. IN THIS CASE; ATC HAD DIFFICULTY UNDERSTANDING OUR PROB. 2) HEADSETS. I'M TYPE RATED IN 5 DIFFERENT JETS. THE CO-CAPT IS TYPED RATED IN 3. WE FLY TOGETHER OFTEN. IN OTHER JETS; WE USED LIGHT WT HEADSETS WITH BOOM MICROPHONES. IN THIS ACFT; THE TRAINING INSTRUCTOR HAD INDICATED HIS DISLIKE FOR HEADSETS BECAUSE OF THE DIFFICULTY IN USING A QUICK-DONNING MASK. WE ELECTED TO FOLLOW HIS ADVICE; AND USED HAND MICROPHONE AND CABIN SPEAKERS. DURING THIS INCIDENT; NOT ONLY WERE WE UNABLE TO COMMUNICATE EFFECTIVELY DUE TO THE POOR QUALITY OF THE OXYGEN MASK MIKE; BUT I WAS UNABLE TO HEAR WHAT THE CO-CAPT WAS TELLING ATC AT THIS CRUCIAL TIME; OR FOR US TO COM OTHER THAN BY SHOUTING; REQUIRING REMOVAL OFTHE MASK. THERE WAS A LOT OF COCKPIT NOISE DUE TO HIGH INDICATED SPEED CAUSED BY THE NECESSITY TO STAY BELOW RVSM AIRSPACE (INDICATED SPEEDS -- AND COCKPIT AIR NOISE -- ARE LOWER AT HIGH ALTS). IN THE SABRELINER; THERE IS AN EFFECTIVE (BUT NOISY) AIR BRAKE LOCATED ON THE BOTTOM OF THE ACFT BEHIND THE COCKPIT. EFFECTIVE COCKPIT COM WAS HINDERED. I AM GLAD WE HAVE FLOWN TOGETHER OFTEN. 3) AS A RESULT OF THIS INCIDENT; WE ARE MAKING CHANGES TO OUR EQUIPMENT AND PROCS. WE HAVE PURCHASED A DIFFERENT STYLE OF QUICK-DONNING OXYGEN MASK; COMPATIBLE WITH LIGHT WT HEADSETS. WE WILL BE USING LIGHT WT HEADSETS; SO WE CAN MAKE USE OF THE COCKPIT INTERCOM FOR INTER-PLT COM. 4) AS A RESULT OF OUR OWN EXPERIENCES IN ACFT DEPRESSURIZATION; I WILL USE THE PROC THAT HAS WORKED WELL FOR ME; I WILL PUT THE QUICK-DONNING MASK ON OVER THE EARPIECES AND MICROPHONE TUBE OF THE REGULAR HEADSET; RATHER THAN TAKING THE HEADSET OFF. THE TIME SPENT REMOVING THE HEADSET BEFORE DONNING THE MASK; AND THE POOR QUALITY OF OXYGEN MASK MICROPHONES MAKES THIS PROC PREFERABLE.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT HE ATTEMPTS TO MENTALLY PREPARE FOR VARIOUS SCENARIOS THAT COULD DEVELOP WHILE AIRBORNE. HE FELT THAT THIS ENABLED THE FLT CREW TO MORE EFFICIENTLY DEAL WITH THIS EMER. HE ALSO STATED THAT THE PROC CALLS FOR REDUCING POWER ON THE R ENGINE TO REDUCE TEMPERATURES IN THE DUCT.

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.