Narrative:

Level at FL370; in IMC; M .835; and smooth air. [We had] thunderstorms on the radar; closest approximately 100 miles ahead. No returns at point of turbulence. I was in galley area; first officer was pilot flying; and relief pilot was in bunk for rest. [We] encountered severe turbulence for less than 10 seconds. Coffee was splashed all over galley (pot was secured in the coffeemaker at the time of incident); I felt myself becoming light for a second. [We] experienced both a stick shaker and airframe buffet. I returned immediately to the cockpit to find the aircraft 500 ft above assigned altitude. Turbulence lessened to moderate for another 5 - 10 seconds. First officer began to maneuver cautiously back to altitude. Autopilot remained engaged. [We were] back in smooth air as we reached FL370. Entire sequence from first indication to smooth air was 20 seconds or less. [We] informed taipei of the altitude excursion and the severe turbulence. A flight that had taken off behind us then reported severe turbulence in the same place. In discussing the event; first officer informed me that there were no returns on the radar at the time of the occurrence. Radar tilt was approximately 1 degree down. Weather was being painted further out; but nothing showed closer than 100 miles. He also stated that at the time of stick shaker/airframe buffet the airspeed had increased immediately to maximum speed (red limit bars) and the amber maneuvering bar came up to the airspeed. Essentially we were both too fast and too slow. No overspeed EICAS message appeared. This occurred for only a brief second. Occurrence was written up in the logbook and an inspection was performed after landing. No damage found.

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Original NASA ASRS Text

Title: B747 flight crew encounters severe turbulence at FL370 in RCTP airspace resulting in a 500 FT altitude gain and both under speed and overspeed warnings.

Narrative: Level at FL370; in IMC; M .835; and smooth air. [We had] thunderstorms on the radar; closest approximately 100 miles ahead. No returns at point of turbulence. I was in galley area; First Officer was pilot flying; and Relief Pilot was in bunk for rest. [We] encountered severe turbulence for less than 10 seconds. Coffee was splashed all over galley (pot was secured in the coffeemaker at the time of incident); I felt myself becoming light for a second. [We] experienced both a stick shaker and airframe buffet. I returned immediately to the cockpit to find the aircraft 500 FT above assigned altitude. Turbulence lessened to moderate for another 5 - 10 seconds. First Officer began to maneuver cautiously back to altitude. Autopilot remained engaged. [We were] back in smooth air as we reached FL370. Entire sequence from first indication to smooth air was 20 seconds or less. [We] informed Taipei of the altitude excursion and the severe turbulence. A flight that had taken off behind us then reported severe turbulence in the same place. In discussing the event; First Officer informed me that there were no returns on the radar at the time of the occurrence. Radar tilt was approximately 1 degree down. Weather was being painted further out; but nothing showed closer than 100 miles. He also stated that at the time of stick shaker/airframe buffet the airspeed had increased immediately to maximum speed (red limit bars) and the amber maneuvering bar came up to the airspeed. Essentially we were both too fast and too slow. No overspeed EICAS message appeared. This occurred for only a brief second. Occurrence was written up in the logbook and an inspection was performed after landing. No damage found.

Data retrieved from NASA's ASRS site as of April 2012 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.