Narrative:

We were cruising at FL370 approaching atl. The flight was routine and we had received no warnings of possible turbulence ahead. The airplane started to feel like it was going through some mountain wave and the passenger seatbelt sign was turned on. The airspeed suddenly increased into the overspeed region of the airspeed tape. The autopilot was engaged at the time and it began its automatic pull-up; then disengaged a few seconds later. The ride suddenly became at least moderate turbulence and I grabbed the PA and made the 'flight attendants be seated' call (they had already taken their seats when we first encountered the 'wave'). At this time; the captain (who was the pilot flying) was trying to slow the airplane. Not only was the overspeed warning going off; but the altitude alert also sounded because we were a little over 300 ft off of the assigned altitude. The captain later told me the airplane climbed despite his applying nose down control inputs. After approximately 5 seconds; the airspeed was brought under control and we were correcting back to our assigned altitude. The captain asked me to get a lower altitude which I was able to do immediately with ATC. I then reported the turbulence to ATC; sent an ACARS message to dispatch; and sent a maintenance code for the overspeed. We later amended our report to dispatch; calling the turbulence severe since the airplane was out of control for a moment (going up when the nose was commanded down); even though I don't think the plane experienced any significant g-forces. As I mentioned earlier; this was a complete surprise to us with the rapidity that the turbulence struck. There had been no heads-up from dispatch; and I don't recall hearing anything from ATC or other airplanes until we were in it. Maybe we had just changed frequencies and word hadn't gotten around the nearby sectors yet. This reinforces the necessity of communicating with dispatch and ATC on the quality of the rides. I have been guilty of not letting them know in the most timely manner in the past -- that will change. Incidentally; I ran into another captain the next day at the hotel who was flying about 40 minutes behind us on the same airway. He said that they got a message from dispatch based on our report and were able to adjust their altitude and avoid the worst of the turbulence. Supplemental information from acn 825359: in level cruise; approximately 50 miles northwest of atl FL370; mach .78; weather radar on; started getting a wave of +/-100 ft of altitude. Turned on fasten seatbelt sign and shortly thereafter entered moderate turbulence.

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Original NASA ASRS Text

Title: A320 flight crew at FL370 experienced light mountain wave which turned into severe turbulence and resulted in an overspeed situation.

Narrative: We were cruising at FL370 approaching ATL. The flight was routine and we had received no warnings of possible turbulence ahead. The airplane started to feel like it was going through some mountain wave and the passenger seatbelt sign was turned on. The airspeed suddenly increased into the overspeed region of the airspeed tape. The autopilot was engaged at the time and it began its automatic pull-up; then disengaged a few seconds later. The ride suddenly became at least moderate turbulence and I grabbed the PA and made the 'Flight Attendants be seated' call (they had already taken their seats when we first encountered the 'wave'). At this time; the Captain (who was the Pilot Flying) was trying to slow the airplane. Not only was the overspeed warning going off; but the altitude alert also sounded because we were a little over 300 FT off of the assigned altitude. The Captain later told me the airplane climbed despite his applying nose down control inputs. After approximately 5 seconds; the airspeed was brought under control and we were correcting back to our assigned altitude. The Captain asked me to get a lower altitude which I was able to do immediately with ATC. I then reported the turbulence to ATC; sent an ACARS message to Dispatch; and sent a maintenance code for the overspeed. We later amended our report to Dispatch; calling the turbulence severe since the airplane was out of control for a moment (going up when the nose was commanded down); even though I don't think the plane experienced any significant G-forces. As I mentioned earlier; this was a complete surprise to us with the rapidity that the turbulence struck. There had been no heads-up from Dispatch; and I don't recall hearing anything from ATC or other airplanes until we were in it. Maybe we had just changed frequencies and word hadn't gotten around the nearby sectors yet. This reinforces the necessity of communicating with Dispatch and ATC on the quality of the rides. I have been guilty of not letting them know in the most timely manner in the past -- that will change. Incidentally; I ran into another Captain the next day at the hotel who was flying about 40 minutes behind us on the same airway. He said that they got a message from Dispatch based on our report and were able to adjust their altitude and avoid the worst of the turbulence. Supplemental information from ACN 825359: In level cruise; approximately 50 miles northwest of ATL FL370; Mach .78; weather radar on; started getting a wave of +/-100 FT of altitude. Turned on fasten seatbelt sign and shortly thereafter entered moderate turbulence.

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.