Narrative:

Flight plan to fly at 37000 ft. There was moderate turbulence at that altitude over NM, so we chose to fly at 41000 ft. Center cleared us to that altitude. The FMS showed that the optimum altitude would have been about 40000 ft. I used vertical speed, 100 FPM, plus maximum continuous power to climb the last 800 ft. The plane held the speed and altitude using 'maximum continuous' power. About newman (el paso) the copilot noticed we were still in 'maximum continuous' power. I elected to select cruise power setting. We settled back and were enjoying a smooth trip when we began to feel a buffet. Much to our surprise, we discovered that the airspeed had bled off about 30 KTS and we were actually 'behind the power curve'. Maximum power did not immediately help, so I disconnected the autoplt, maintained maximum power and began a descent. Declaring an emergency so we could descend. We leveled at 37000 ft airspeed, etc was normal, having returned by 39500 ft. Rest of flight normal. Looking back, I was out of the envelope for that altitude and power setting. Never again will I attempt such an altitude vs. Heavy weight. I will also pay more attention to the FMS. The plane is very honest and forgiving but cannot be mistreated.

Related reports:

Google
 

Original NASA ASRS Text

Title: CLB ABOVE MAX CRUISE ALT TO AVOID TURB. PRESTALL BUFFET, EMER DSCNT.

Narrative: FLT PLAN TO FLY AT 37000 FT. THERE WAS MODERATE TURB AT THAT ALT OVER NM, SO WE CHOSE TO FLY AT 41000 FT. CENTER CLRED US TO THAT ALT. THE FMS SHOWED THAT THE OPTIMUM ALT WOULD HAVE BEEN ABOUT 40000 FT. I USED VERT SPD, 100 FPM, PLUS MAX CONTINUOUS PWR TO CLB THE LAST 800 FT. THE PLANE HELD THE SPD AND ALT USING 'MAX CONTINUOUS' PWR. ABOUT NEWMAN (EL PASO) THE COPLT NOTICED WE WERE STILL IN 'MAX CONTINUOUS' PWR. I ELECTED TO SELECT CRUISE PWR SETTING. WE SETTLED BACK AND WERE ENJOYING A SMOOTH TRIP WHEN WE BEGAN TO FEEL A BUFFET. MUCH TO OUR SURPRISE, WE DISCOVERED THAT THE AIRSPD HAD BLED OFF ABOUT 30 KTS AND WE WERE ACTUALLY 'BEHIND THE PWR CURVE'. MAX PWR DID NOT IMMEDIATELY HELP, SO I DISCONNECTED THE AUTOPLT, MAINTAINED MAX PWR AND BEGAN A DSCNT. DECLARING AN EMER SO WE COULD DSND. WE LEVELED AT 37000 FT AIRSPD, ETC WAS NORMAL, HAVING RETURNED BY 39500 FT. REST OF FLT NORMAL. LOOKING BACK, I WAS OUT OF THE ENVELOPE FOR THAT ALT AND PWR SETTING. NEVER AGAIN WILL I ATTEMPT SUCH AN ALT VS. HEAVY WT. I WILL ALSO PAY MORE ATTN TO THE FMS. THE PLANE IS VERY HONEST AND FORGIVING BUT CANNOT BE MISTREATED.

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.