Narrative:

Due to intermittent turbulence at FL370, we decided to climb to FL410. The FMC indicated it could be done and ATC and PIREPS indicated the ride was smooth. The climb took a bit of time during the last 1500 ft to FL410 due to turbulence. The aircraft was at turbulence penetration speed. We remarked that we might want to let ATC know about the slow climb. Also, the aircraft had the left engine anti-ice locked open due to MEL restr. After leveloff at FL410, the aircraft accelerated slowly to cruise speed. Aircraft weight was about 184000 pounds. Several mins later, after leveloff, I told the captain I was going to take care of some other things, and to watch the aircraft. A few mins later, I heard him say, 'how did we get so slow?' the aircraft had slowed some 35 KTS for no reason. All proper modes were engaged. We asked for and received a descent to FL370 to recover the lost airspeed. We used a maximum thrust setting until descent clearance was received. There was no stall warning generated, nor was the aircraft indicating any buffet. No harsh maneuvers were made to regain airspeed. We rechked the aircraft weight and balance and the numbers worked out. The FMC weight agreed with a manually calculated weight. The FMC still indicated a maximum altitude of 41500 ft. The only thing I can figure is that 1 of 2 things could have happened: some kind of mountain wave, or there was not enough thrust available from the left engine due to the anti-ice being on. There was no altitude restr listed or warning that you might not be able to fly at altitude for a given weight. Their only power correction applied to climb settings.

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Original NASA ASRS Text

Title: B757-200 CREW GOT ON THE BACK SIDE OF THE PWR CURVE, AND WAS REQUIRED TO DSND TO RECOVER AIRSPD.

Narrative: DUE TO INTERMITTENT TURB AT FL370, WE DECIDED TO CLB TO FL410. THE FMC INDICATED IT COULD BE DONE AND ATC AND PIREPS INDICATED THE RIDE WAS SMOOTH. THE CLB TOOK A BIT OF TIME DURING THE LAST 1500 FT TO FL410 DUE TO TURB. THE ACFT WAS AT TURB PENETRATION SPD. WE REMARKED THAT WE MIGHT WANT TO LET ATC KNOW ABOUT THE SLOW CLB. ALSO, THE ACFT HAD THE L ENG ANTI-ICE LOCKED OPEN DUE TO MEL RESTR. AFTER LEVELOFF AT FL410, THE ACFT ACCELERATED SLOWLY TO CRUISE SPD. ACFT WT WAS ABOUT 184000 LBS. SEVERAL MINS LATER, AFTER LEVELOFF, I TOLD THE CAPT I WAS GOING TO TAKE CARE OF SOME OTHER THINGS, AND TO WATCH THE ACFT. A FEW MINS LATER, I HEARD HIM SAY, 'HOW DID WE GET SO SLOW?' THE ACFT HAD SLOWED SOME 35 KTS FOR NO REASON. ALL PROPER MODES WERE ENGAGED. WE ASKED FOR AND RECEIVED A DSCNT TO FL370 TO RECOVER THE LOST AIRSPD. WE USED A MAX THRUST SETTING UNTIL DSCNT CLRNC WAS RECEIVED. THERE WAS NO STALL WARNING GENERATED, NOR WAS THE ACFT INDICATING ANY BUFFET. NO HARSH MANEUVERS WERE MADE TO REGAIN AIRSPD. WE RECHKED THE ACFT WT AND BAL AND THE NUMBERS WORKED OUT. THE FMC WT AGREED WITH A MANUALLY CALCULATED WT. THE FMC STILL INDICATED A MAX ALT OF 41500 FT. THE ONLY THING I CAN FIGURE IS THAT 1 OF 2 THINGS COULD HAVE HAPPENED: SOME KIND OF MOUNTAIN WAVE, OR THERE WAS NOT ENOUGH THRUST AVAILABLE FROM THE L ENG DUE TO THE ANTI-ICE BEING ON. THERE WAS NO ALT RESTR LISTED OR WARNING THAT YOU MIGHT NOT BE ABLE TO FLY AT ALT FOR A GIVEN WT. THEIR ONLY PWR CORRECTION APPLIED TO CLB SETTINGS.

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.