An ERJ flight crew encountered what appeared to be wave action when starting a descent and; instead; gained 500 FT prior to establishing a controlled descent.
Synopsis
An ERJ flight crew encountered what appeared to be wave action when starting a descent and; instead; gained 500 FT prior to establishing a controlled descent.
Narrative
We were assigned an initial cruising altitude of 33;000 FT. Once we reached our initial altitude we were in a haze layer and there was pretty consistent light chop and thought that if we went up to FL370 we might get a better ride have a better view of any weather ahead of us. We climbed to FL370 and were still in the haze but had no returns on our radar screen. It was mostly smooth with some rare ripples of light chop and since we had been dealing with the weather/turbulence earlier in the day the Captain decided to leave the seatbelt sign on. We were in communications with the Flight Attendant about the possibility of turbulence the whole flight. ATC assigned us M.77 for spacing into DCA. As we were over the LUISE Intersection we were issued a descent clearance to FL310. I spun in the altitude; verified it with the captain; and set a descent rate of 1;000 FPM on the VS selector. As soon as we started our decent the aircraft pitched up and began about a 2;500 FPM climb. I instantly pulled the power to idle and overrode the autopilot to put us into a stable descent attitude and once the aircraft was established in a stable descent I reengaged the autopilot. During all this the Captain advised ATC that we were unable to hold altitude and that we would advise when we were established back on our descent. The whole event only lasted 10 or so seconds and after that the flight continued smoothly and without incident. The turbulence wasn't the normal jarring bumps as it was more of a gentle sensation as if you were riding atop a wave. Dispatch called us a minute or so after the event to tell us that we should be crossing the worst of the weather in the next few minutes. While the Captain was talking to Dispatch I advised ATC that we would be unable to maintain M.77 due to the weather and slowed the aircraft. No passengers or crew were injured and there weren't any conflicts with traffic. The aircraft operated normally throughout the whole flight and event. We knew we were crossing weather and were very active in monitoring the situation. We made multiple calls to ATC asking about how the rides were at our altitudes. All SOP's were complied with.
Second reporter narrative
The First Officer (pilot flying) selected Vertical Speed (VS) minus 1;000 with the autopilot engaged. The aircraft started to descend and at 36;900 FT MSL we encountered this wave like turbulence and it took the airplane up to 37;500 in a matter of seconds. It was a rather smooth pitch change and not a violent chop. The First Officer dialed minus 2;000 FPM and then manually corrected the aircraft to a negative pitch. The airplane corrected to a descent of minus 2;500 FPM then VS minus 1;000 was imputed and the aircraft oscillated until that desired rate of change was obtained.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.