Narrative:

We were filed 37000 ft. The captain wanted to save gas so he proceeded to program different scenarios into the computer that would hopefully improve our fuel economy. He appeared to be very experienced at milking more fuel out of the normal planned situation. I was convinced his knowledge exceeded my level of training and experience (i.e., sticking with the planned program). Thus, he asked for 41000 and received clearance. As we started our slow climb toward FL410 the computer flashed that 41000 ft was above our maximum altitude by about 400 ft (I don't recall the exact figure). So I inquired as to whether we should try 41000 ft at this time. The captain assured me we would be fine. I personally recalled exceeding the computer altitude limit on numerous other flts with no problems, although maybe not by 400 ft. Therefore, I put it to rest. Within my mind everything seemed all right. Upon level off at FL410 (I.east, the autoplt held altitude and the autothrottle held airspeed). In actuality, my hindsight revealed we were in fact too high for our gross weight (i.e., we were sort of behind the power curve). Since we had resolved within our minds that we could fly at 41000 ft we never noticed the autothrottles slow creep toward maximum EPR (power for cruise). The captain got up to use the bathroom. I checked and even at that point everything appeared normal (i.e., autoplt holding course, attitude and altitude and autothrottle still holding target (bug) airspeed. The captain couldn't' have been gone more than 3 mins when the next thing I noticed we were drifting into a speed buffet. I checked my instruments to find my airspeed bleeding off. By this time, the captain returns to the cockpit and notices me trying to add what little power I have left (the autothrottle stopped at maximum cruise rather than maximum maximum. After a brief discussion as to what was happening, we ruled out airframe/engine icing and the captain said 'stall.' so I disengaged autoplt, eased the nose down (2000 FPM) and the buffet stops. Whenever I tried to raise the nose, the buffet returned. Thus, I kept the nose down until I recovered all of my airspeed (lowest speed about 210 KTS). I was able to level off at 35000 ft buffet free. The rest of the flight proved uneventful. We never actually got close to stall, but only low speed buffet because we never got a 'stick shaker.'

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Original NASA ASRS Text

Title: CAPT OF AN LGT ATTEMPTED TO OPERATE AT A HIGHER ALT THAN THE ACFT WT WOULD ALLOW, RESULTING IN A STALL BUFFET DUE TO LOW AIRSPD.

Narrative: WE WERE FILED 37000 FT. THE CAPT WANTED TO SAVE GAS SO HE PROCEEDED TO PROGRAM DIFFERENT SCENARIOS INTO THE COMPUTER THAT WOULD HOPEFULLY IMPROVE OUR FUEL ECONOMY. HE APPEARED TO BE VERY EXPERIENCED AT MILKING MORE FUEL OUT OF THE NORMAL PLANNED SIT. I WAS CONVINCED HIS KNOWLEDGE EXCEEDED MY LEVEL OF TRAINING AND EXPERIENCE (I.E., STICKING WITH THE PLANNED PROGRAM). THUS, HE ASKED FOR 41000 AND RECEIVED CLRNC. AS WE STARTED OUR SLOW CLB TOWARD FL410 THE COMPUTER FLASHED THAT 41000 FT WAS ABOVE OUR MAX ALT BY ABOUT 400 FT (I DON'T RECALL THE EXACT FIGURE). SO I INQUIRED AS TO WHETHER WE SHOULD TRY 41000 FT AT THIS TIME. THE CAPT ASSURED ME WE WOULD BE FINE. I PERSONALLY RECALLED EXCEEDING THE COMPUTER ALT LIMIT ON NUMEROUS OTHER FLTS WITH NO PROBS, ALTHOUGH MAYBE NOT BY 400 FT. THEREFORE, I PUT IT TO REST. WITHIN MY MIND EVERYTHING SEEMED ALL RIGHT. UPON LEVEL OFF AT FL410 (I.E, THE AUTOPLT HELD ALT AND THE AUTOTHROTTLE HELD AIRSPD). IN ACTUALITY, MY HINDSIGHT REVEALED WE WERE IN FACT TOO HIGH FOR OUR GROSS WT (I.E., WE WERE SORT OF BEHIND THE PWR CURVE). SINCE WE HAD RESOLVED WITHIN OUR MINDS THAT WE COULD FLY AT 41000 FT WE NEVER NOTICED THE AUTOTHROTTLES SLOW CREEP TOWARD MAX EPR (PWR FOR CRUISE). THE CAPT GOT UP TO USE THE BATHROOM. I CHKED AND EVEN AT THAT POINT EVERYTHING APPEARED NORMAL (I.E., AUTOPLT HOLDING COURSE, ATTITUDE AND ALT AND AUTOTHROTTLE STILL HOLDING TARGET (BUG) AIRSPD. THE CAPT COULDN'T' HAVE BEEN GONE MORE THAN 3 MINS WHEN THE NEXT THING I NOTICED WE WERE DRIFTING INTO A SPD BUFFET. I CHKED MY INSTS TO FIND MY AIRSPD BLEEDING OFF. BY THIS TIME, THE CAPT RETURNS TO THE COCKPIT AND NOTICES ME TRYING TO ADD WHAT LITTLE PWR I HAVE LEFT (THE AUTOTHROTTLE STOPPED AT MAX CRUISE RATHER THAN MAX MAX. AFTER A BRIEF DISCUSSION AS TO WHAT WAS HAPPENING, WE RULED OUT AIRFRAME/ENG ICING AND THE CAPT SAID 'STALL.' SO I DISENGAGED AUTOPLT, EASED THE NOSE DOWN (2000 FPM) AND THE BUFFET STOPS. WHENEVER I TRIED TO RAISE THE NOSE, THE BUFFET RETURNED. THUS, I KEPT THE NOSE DOWN UNTIL I RECOVERED ALL OF MY AIRSPD (LOWEST SPD ABOUT 210 KTS). I WAS ABLE TO LEVEL OFF AT 35000 FT BUFFET FREE. THE REST OF THE FLT PROVED UNEVENTFUL. WE NEVER ACTUALLY GOT CLOSE TO STALL, BUT ONLY LOW SPD BUFFET BECAUSE WE NEVER GOT A 'STICK SHAKER.'

Data retrieved from NASA's ASRS site as of July 2007 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.