Flight Crew Air Transport Pilot (ATP)
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Flight Crew Regained Aircraft Control; Flight Crew Took Evasive Action
Weather
While flying over LAS at FL380 we encountered moderate mountain wave. We had significant airspeed fluctuations and as a result requested a lower altitude. We descended to FL350. 40 miles south of LAS we encountered additional mountain wave which forced an uncommanded climb of 400 FT with the autopilot fighting to maintain FL350. We immediately informed ATC of the mountain wave activity and we received a clearance to descend to FL280. A split second later we encountered what I would consider to be extreme mountain wave and moderate turbulence. We had an almost instant airspeed increase from Mach .75 to the max airspeed checker board of roughly Mach .82. The trend continued to increase even while I had the thrust levers at idle and spoilers at max deployment. The condition worsened and I was forced to disconnect the autopilot and pitch the nose up to prevent an extreme overspeed condition. At approximately five degrees nose up and the aircraft climbing at 400 FT/min. We had a loss of 60 KTS in airspeed instantly. At this point I slammed the flight spoilers to retract and the thrust levers to max and pitched the nose down to six degrees nose down. Now at 220 KTS indicated we were fighting to regain airspeed. Mind you this happened so fast we were acting on instinct and with the moderate turbulence it was a bit of a challenge. It took a 2;500 FPM descent rate and 2;000 FT to regain our airspeed. We leveled as cleared at FL280. We then gave a PIREP of extreme mountain wave with airspeed fluctuations of 60 KTS. We checked on our flight attendants and passengers and everyone was okay. We landed without further incident.Had we known to avoid this area it would have been avoided. We knew there would be turbulence and mountain wave. However we fly through these types of conditions regularly without problem. In this instance it would seem that we were the guinea pigs that prevented other flights from entering that area. I suppose my biggest suggestion to pilots is to respect mountain wave's potentially extreme elements associated with an unstable air-mass. Additionally lower altitudes are always better when navigating such areas. Perhaps if Dispatch were to have an Altitude Risk Assessment tool based on areas of unstable air it would increase our margins of safety. Had we stayed at our filed altitude I think we would have been in big trouble. Additionally it may be helpful to perform high altitude wind-shear escape maneuvers in the simulator. My First Officer reverted to our low altitude wind shear escape training by making call outs on airspeed and trend vectors while I was fighting to keep the aircraft under control. That was very helpful. I don't think current technology can predict the small area of wind shear we encountered as this was a very isolated event in the area. Obviously; avoidance would have been the best measure.
A CRJ-700 Captain describes an encounter with 'extreme' mountain wave activity near LAS.