B737-300
Flight Crew Last 90 Days 213; Flight Crew Type 15000
Inflight Event / Encounter Wake Vortex Encounter
Flight Crew Regained Aircraft Control
Aircraft; Environment - Non Weather Related
Climbing through approximately FL250; we encountered significant wake turbulence and accompanying abrupt flight path interruption/momentary moderate-to-severe turbulence-like event exacerbated by lack of yaw damper (MEL'd). Pilot flying (First Officer) did an excellent job of immediately disconnecting the autopilot and recovering the aircraft to a stable attitude. We had considered the MEL'd yaw damper and potential implications during our preflight activities. The weather package indicated no significant weather or turbulence on our planned route or destination. We researched (per the MEL) the flap maneuvering speeds (22-3) and ensured the remaining provisos were complied with. (This aircraft had flown approximately eight legs since the yaw damper had been deferred the previous day.)We briefed the flight attendants regarding the anticipated more uncomfortable ride (especially for the B) and communicated with them throughout the flight regarding their safety and status. After the upset; I immediately made a PA describing to the customers what had occurred and then checked on the flight attendants. Despite light-to-moderate chop experienced at FL340 until west of JOT (ATC reported no smooth altitudes until 'west of the lake' (Michigan); our flight attendants never complained nor did they report any issues with our customers.Dispatch/Maintenance should restrict aircraft with inoperative yaw dampers to short haul routes and should prioritize immediate repair. If this MEL is considered safe (questionable); then pilots should receive training on the flight characteristics with the yaw damper inoperative. Consideration should be given to additional provisions within the MEL language restricting to 'flights one hour or less or no significant weather or turbulence enroute;' and perhaps ATC should be informed and require a minimum in-trail separation. (Once we climbed above the con level; we saw our threat. Until then we were not aware we were climbing behind another aircraft on our route.) Customers should receive some sort of compensation for enduring an (unnecessary) rough ride.
B737-300 Captain reported control difficulties when they encountered wake turbulence at FL250 in an aircraft with the yaw damper out of service.