Narrative:

Encountered moderate turbulence at FL410. Airspeed increased to clacker. We reduced power and airspeed rapidly slowed. Stick shaker occurred for short duration and we advanced power to maximum. Aircraft descended approximately 500 ft and then leveled. We advised ATC that we were unable to maintain altitude and needed to turn to avoid WX. Center cleared us for turn to avoid WX; said no other traffic was in the area; and to climb to and maintain FL410 when able. The aircraft initially stabilized at approximately FL405; then descended; leveled; and descended for about 1500 ft total. Airspeed deviation was probably +/-5-10 KTS. When we were clear of the turbulence the aircraft accelerated like normal and climbed back to FL410 in a normal manner. During the altitude deviation the right wing body overheat light illuminated. We later determined that the light was a false indication and not a contributing factor. Neither first officer nor I are sure what exactly what WX phenomena we encountered; though I suspect it was a downdraft from the top of some convective activity. My initial thoughts were that we had stalled; but first officer has been through the high altitude stall training and said that the simulator responded differently than what we experienced. We neither one had any solutions for avoidance other than maybe having the radar on earlier. We didn't have it on because it looked like we were entering a high haze layer with no WX activity associated with it. Also; there were no reports from other aircraft about any rough air. Supplemental information from acn 703869: third leg of 3 on day #1 of 3-DAY with third captain. We were at FL410. We were slightly above the aircraft optimum altitude; so we only had a 1.3 margin. We did not have the WX radar but we did have a haze layer below us. We started to pick up some light chop so the captain advised the passenger to situation and turned on the seatbelt sign. He then queried ATC and there were no bad ride reports given. Right after that we got into moderate and the captain told the flight attendants to take a seat. I had started to call ATC and was going to tell them about the ride and ask for a new altitude when the airspeed went into the clacker range. I immediately pulled back the throttles and turned on the WX radar. It was pitched up and I dialed it back down. The captain grabbed the throttles and pushed them back to normal cruise and we had a moment of clacker and then a complete loss of airspeed and altitude. We experienced this for about 30 seconds and then everything was smooth for the remainder of the flight. I asked for a block altitude while the captain flew the aircraft. I then became the PF again and the captain notified the company. We probably should have had the WX radar on because of the haze layer below us. I believe we did not give ourselves enough vertical separation from WX forming below us. I had just come from our destination and had told the captain it had been a smooth flight. We both had checked the WX prior to departing.

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Original NASA ASRS Text

Title: A B737-700 OVER ORF AT FL410 IN A HAZE LAYER EXPERIENCED OVERSPD WARNING AND STALL WARNINGS WITH TURB AND AN UNCTLABLE DSCNT.

Narrative: ENCOUNTERED MODERATE TURB AT FL410. AIRSPD INCREASED TO CLACKER. WE REDUCED PWR AND AIRSPD RAPIDLY SLOWED. STICK SHAKER OCCURRED FOR SHORT DURATION AND WE ADVANCED PWR TO MAX. ACFT DSNDED APPROX 500 FT AND THEN LEVELED. WE ADVISED ATC THAT WE WERE UNABLE TO MAINTAIN ALT AND NEEDED TO TURN TO AVOID WX. CTR CLRED US FOR TURN TO AVOID WX; SAID NO OTHER TFC WAS IN THE AREA; AND TO CLB TO AND MAINTAIN FL410 WHEN ABLE. THE ACFT INITIALLY STABILIZED AT APPROX FL405; THEN DSNDED; LEVELED; AND DSNDED FOR ABOUT 1500 FT TOTAL. AIRSPD DEV WAS PROBABLY +/-5-10 KTS. WHEN WE WERE CLR OF THE TURB THE ACFT ACCELERATED LIKE NORMAL AND CLBED BACK TO FL410 IN A NORMAL MANNER. DURING THE ALTDEV THE R WING BODY OVERHEAT LIGHT ILLUMINATED. WE LATER DETERMINED THAT THE LIGHT WAS A FALSE INDICATION AND NOT A CONTRIBUTING FACTOR. NEITHER FO NOR I ARE SURE WHAT EXACTLY WHAT WX PHENOMENA WE ENCOUNTERED; THOUGH I SUSPECT IT WAS A DOWNDRAFT FROM THE TOP OF SOME CONVECTIVE ACTIVITY. MY INITIAL THOUGHTS WERE THAT WE HAD STALLED; BUT FO HAS BEEN THROUGH THE HIGH ALT STALL TRAINING AND SAID THAT THE SIMULATOR RESPONDED DIFFERENTLY THAN WHAT WE EXPERIENCED. WE NEITHER ONE HAD ANY SOLUTIONS FOR AVOIDANCE OTHER THAN MAYBE HAVING THE RADAR ON EARLIER. WE DIDN'T HAVE IT ON BECAUSE IT LOOKED LIKE WE WERE ENTERING A HIGH HAZE LAYER WITH NO WX ACTIVITY ASSOCIATED WITH IT. ALSO; THERE WERE NO RPTS FROM OTHER ACFT ABOUT ANY ROUGH AIR. SUPPLEMENTAL INFO FROM ACN 703869: THIRD LEG OF 3 ON DAY #1 OF 3-DAY WITH THIRD CAPT. WE WERE AT FL410. WE WERE SLIGHTLY ABOVE THE ACFT OPTIMUM ALT; SO WE ONLY HAD A 1.3 MARGIN. WE DID NOT HAVE THE WX RADAR BUT WE DID HAVE A HAZE LAYER BELOW US. WE STARTED TO PICK UP SOME LIGHT CHOP SO THE CAPT ADVISED THE PAX TO SIT AND TURNED ON THE SEATBELT SIGN. HE THEN QUERIED ATC AND THERE WERE NO BAD RIDE RPTS GIVEN. RIGHT AFTER THAT WE GOT INTO MODERATE AND THE CAPT TOLD THE FLT ATTENDANTS TO TAKE A SEAT. I HAD STARTED TO CALL ATC AND WAS GOING TO TELL THEM ABOUT THE RIDE AND ASK FOR A NEW ALT WHEN THE AIRSPD WENT INTO THE CLACKER RANGE. I IMMEDIATELY PULLED BACK THE THROTTLES AND TURNED ON THE WX RADAR. IT WAS PITCHED UP AND I DIALED IT BACK DOWN. THE CAPT GRABBED THE THROTTLES AND PUSHED THEM BACK TO NORMAL CRUISE AND WE HAD A MOMENT OF CLACKER AND THEN A COMPLETE LOSS OF AIRSPD AND ALT. WE EXPERIENCED THIS FOR ABOUT 30 SECONDS AND THEN EVERYTHING WAS SMOOTH FOR THE REMAINDER OF THE FLT. I ASKED FOR A BLOCK ALT WHILE THE CAPT FLEW THE ACFT. I THEN BECAME THE PF AGAIN AND THE CAPT NOTIFIED THE COMPANY. WE PROBABLY SHOULD HAVE HAD THE WX RADAR ON BECAUSE OF THE HAZE LAYER BELOW US. I BELIEVE WE DID NOT GIVE OURSELVES ENOUGH VERT SEPARATION FROM WX FORMING BELOW US. I HAD JUST COME FROM OUR DEST AND HAD TOLD THE CAPT IT HAD BEEN A SMOOTH FLT. WE BOTH HAD CHKED THE WX PRIOR TO DEPARTING.

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.