Narrative:

We leveled at FL340 75 mi east of cluts intersection, speed at about mach .79 and expected aircraft to accelerate to mach .84. We were at maximum climb power but aircraft slowed, stabilizing at mach .72 for about 10 mins. Nearing cheak intersection and realizing we were not going to accelerate, we requested FL320 from ATC through hnl radio (HF). It was denied because of traffic. We began to experience some wave activity and turbulence. Our airspeed started to decrease. The first officer was flying on autoplt and was trying to trade some altitude for airspeed to no avail. At this time we were about 650000 pounds, which is 9000 pounds below maximum cruise weight for standard temperature plus 10 degrees at 340. We could not understand why we could not maintain speed and altitude. The first officer disengaged the autoplt and the captain told him to descend to FL335 and try to get airspeed back. At FL335 the aircraft pitched up rapidly to FL340 with further loss of airspeed to mach .67. We went through another cycle from FL340 to FL335 to FL340 with more airspeed loss and the captain took control of the aircraft. We were still in wave action and light turbulence and pitch instability. The captain had no better luck controling the aircraft than the first officer had. After another cycle from FL340 to FL335, we were still descending through FL335 and slowing below 250 KIAS. The captain observed on TCASII traffic was approximately 10 mi behind us and to our left and 1500 ft below us when we got the first stickshaker. The captain told the first officer to tell hnl that we were turning right, off course, and descending to FL300 and declaring an emergency. It was hard to tell if we were in turbulence or in a stall buffet. We descended rapidly with maximum continuous power set in order to get below traffic and try to get the speed back. We leveled at FL300 and mach .84 at 10 mi right of course. We coordinated with hnl radio for FL300 and a return to on course. At FL300 we could hold mach .84 at normal cruise power and we advised hnl radio the emergency was over. Conclusion: I think there may have been an error on the weight manifest, making our gross weight somewhat more than stated, although this does not appear to be the case. Also I feel now that if there is wave action and turbulence, the crew should pick a cruise altitude not based on maximum cruise weight but on optimum cruise weight.

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Original NASA ASRS Text

Title: AN ACR B-747 GOT BEHIND THE PWR CURVE AND NEARLY STALLED.

Narrative: WE LEVELED AT FL340 75 MI E OF CLUTS INTXN, SPD AT ABOUT MACH .79 AND EXPECTED ACFT TO ACCELERATE TO MACH .84. WE WERE AT MAX CLB PWR BUT ACFT SLOWED, STABILIZING AT MACH .72 FOR ABOUT 10 MINS. NEARING CHEAK INTXN AND REALIZING WE WERE NOT GOING TO ACCELERATE, WE REQUESTED FL320 FROM ATC THROUGH HNL RADIO (HF). IT WAS DENIED BECAUSE OF TFC. WE BEGAN TO EXPERIENCE SOME WAVE ACTIVITY AND TURB. OUR AIRSPD STARTED TO DECREASE. THE FO WAS FLYING ON AUTOPLT AND WAS TRYING TO TRADE SOME ALT FOR AIRSPD TO NO AVAIL. AT THIS TIME WE WERE ABOUT 650000 LBS, WHICH IS 9000 LBS BELOW MAX CRUISE WT FOR STANDARD TEMP PLUS 10 DEGS AT 340. WE COULD NOT UNDERSTAND WHY WE COULD NOT MAINTAIN SPD AND ALT. THE FO DISENGAGED THE AUTOPLT AND THE CAPT TOLD HIM TO DSND TO FL335 AND TRY TO GET AIRSPD BACK. AT FL335 THE ACFT PITCHED UP RAPIDLY TO FL340 WITH FURTHER LOSS OF AIRSPD TO MACH .67. WE WENT THROUGH ANOTHER CYCLE FROM FL340 TO FL335 TO FL340 WITH MORE AIRSPD LOSS AND THE CAPT TOOK CTL OF THE ACFT. WE WERE STILL IN WAVE ACTION AND LIGHT TURB AND PITCH INSTABILITY. THE CAPT HAD NO BETTER LUCK CTLING THE ACFT THAN THE FO HAD. AFTER ANOTHER CYCLE FROM FL340 TO FL335, WE WERE STILL DSNDING THROUGH FL335 AND SLOWING BELOW 250 KIAS. THE CAPT OBSERVED ON TCASII TFC WAS APPROX 10 MI BEHIND US AND TO OUR L AND 1500 FT BELOW US WHEN WE GOT THE FIRST STICKSHAKER. THE CAPT TOLD THE FO TO TELL HNL THAT WE WERE TURNING R, OFF COURSE, AND DSNDING TO FL300 AND DECLARING AN EMER. IT WAS HARD TO TELL IF WE WERE IN TURB OR IN A STALL BUFFET. WE DSNDED RAPIDLY WITH MAX CONTINUOUS PWR SET IN ORDER TO GET BELOW TFC AND TRY TO GET THE SPD BACK. WE LEVELED AT FL300 AND MACH .84 AT 10 MI R OF COURSE. WE COORDINATED WITH HNL RADIO FOR FL300 AND A RETURN TO ON COURSE. AT FL300 WE COULD HOLD MACH .84 AT NORMAL CRUISE PWR AND WE ADVISED HNL RADIO THE EMER WAS OVER. CONCLUSION: I THINK THERE MAY HAVE BEEN AN ERROR ON THE WT MANIFEST, MAKING OUR GROSS WT SOMEWHAT MORE THAN STATED, ALTHOUGH THIS DOES NOT APPEAR TO BE THE CASE. ALSO I FEEL NOW THAT IF THERE IS WAVE ACTION AND TURB, THE CREW SHOULD PICK A CRUISE ALT NOT BASED ON MAX CRUISE WT BUT ON OPTIMUM CRUISE WT.

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.