Narrative:

Enroute at cruise altitude of FL400; both pilots noted a line of weather approximately 100 miles ahead. Upon additional observation; we determined our flight path would be well above the clouds. We also noted two aircraft ahead on the same route; both at FL360. We asked ATC if any aircraft ahead on our route had encountered adverse conditions or deviated due to weather. ATC responded that no such actions or reports had occurred. Our flight remained in smooth conditions and several minutes later entered and remained in hazy cloud conditions; thus restricting our visibility. We noted the aircraft ahead not changing altitude or route. A few minutes later we encountered convective; windshear-type activity which initially caused the aircraft to accelerate and begin to climb. Almost immediately thereafter; the aircraft rapidly decelerated and began to descend. The autopilot went to cws mode. The PF disconnected the autopilot in order to manually control aircraft attitude. The autothrottles continued to function. The PF acted to override the autothrottles as necessary to respond to the rapid changes in airspeed. The PNF immediately illuminated the seat belt sign and; via the P.a.; notified the passengers and flight attendants to remained seated with seat belts fastened. The PNF then requested a lower altitude from ATC. ATC cleared us to descend to and maintain FL370. During the convective activity the aircraft climbed a few hundred ft; then descended approximately 1;000 ft. Our airspeed initially increased approximately ten KTS; then decreased approximately 20-30 KTS. During the encounter we experienced stick shaker intermittently and difficulty maintaining airspeed and altitude. Maintaining a desired descent rate was also intermittently very difficult. Approximately 60-90 seconds after the beginning of the encounter we entered clear air with good visibility; no windshear-type activity; and smooth conditions. We leveled the aircraft at FL370. The PNF confirmed with ATC our clearance at FL370. He then confirmed with the flight attendants their safety and that of all passengers. He also notified ATC and company dispatch of the location and type of conditions we experienced. The flight continued to our destination normally. On the ground; the captain further discussed the encounter with dispatch via telephone and ACARS. I would suggest a greater distance of deviation from any convective weather would lessen the likelihood of such an event. This type of greater deviation should be taken any time convective activity is suspected or unsure. This type of greater deviation should be taken regardless of ATC reports or lack thereof. This type of greater deviation should be taken regardless of a lack of reports from other aircraft.

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Original NASA ASRS Text

Title: A B737-700 encountered convective windshear activity at FL400 which resulted in a 10 KT speed increase with a climb; followed by a 20-30 FT speed decrease and a 1;000 FT altitude loss with the stick shaker.

Narrative: Enroute at cruise altitude of FL400; both pilots noted a line of weather approximately 100 miles ahead. Upon additional observation; we determined our flight path would be well above the clouds. We also noted two aircraft ahead on the same route; both at FL360. We asked ATC if any aircraft ahead on our route had encountered adverse conditions or deviated due to weather. ATC responded that no such actions or reports had occurred. Our flight remained in smooth conditions and several minutes later entered and remained in hazy cloud conditions; thus restricting our visibility. We noted the aircraft ahead not changing altitude or route. A few minutes later we encountered convective; windshear-type activity which initially caused the aircraft to accelerate and begin to climb. Almost immediately thereafter; the aircraft rapidly decelerated and began to descend. The autopilot went to CWS mode. The PF disconnected the autopilot in order to manually control aircraft attitude. The autothrottles continued to function. The PF acted to override the autothrottles as necessary to respond to the rapid changes in airspeed. The PNF immediately illuminated the seat belt sign and; via the P.A.; notified the passengers and flight attendants to remained seated with seat belts fastened. The PNF then requested a lower altitude from ATC. ATC cleared us to descend to and maintain FL370. During the convective activity the aircraft climbed a few hundred FT; then descended approximately 1;000 FT. Our airspeed initially increased approximately ten KTS; then decreased approximately 20-30 KTS. During the encounter we experienced stick shaker intermittently and difficulty maintaining airspeed and altitude. Maintaining a desired descent rate was also intermittently very difficult. Approximately 60-90 seconds after the beginning of the encounter we entered clear air with good visibility; no windshear-type activity; and smooth conditions. We leveled the aircraft at FL370. The PNF confirmed with ATC our clearance at FL370. He then confirmed with the flight attendants their safety and that of all passengers. He also notified ATC and company Dispatch of the location and type of conditions we experienced. The flight continued to our destination normally. On the ground; the Captain further discussed the encounter with Dispatch via telephone and ACARS. I would suggest a greater distance of deviation from any convective weather would lessen the likelihood of such an event. This type of greater deviation should be taken any time convective activity is suspected or unsure. This type of greater deviation should be taken regardless of ATC reports or lack thereof. This type of greater deviation should be taken regardless of a lack of reports from other aircraft.

Data retrieved from NASA's ASRS site as of July 2013 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.