B737-800
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Last 90 Days 243
Communication Breakdown
ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation - Speed All Types; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Flight Crew Regained Aircraft Control
Weather; Human Factors
We were climbing through FL330 on our way to FL390 when we encountered significant mountain wave. The airspeed was rapidly moving to the MMO limit. The FO (PF) (First Officer; Pilot Flying) disconnected the autothrottles and autopilot and pitched to arrest the airspeed. We noticed that we were climbing in excess of 8000 fpm and the airspeed continued climbing through the MMO limit. There was no clacker but I noted .824 Mach for approximately 15 seconds. I told the FO not to reduce the power too much and to expect the trend to reverse violently possibly resulting in a stall. We made it up to FL385 when the trend did reverse and the airspeed quickly dropped to 220 knots; top of the amber band - losing in excess of 60 knots; even while the FO was pitching down and with emergency thrust. During the low airspeed/pitch down I attempted to contact ATC for a descent clearance but couldn't get 'a word in edgewise'. The Controller seemed to be unusually busy with routine communication; possibly working several sectors at once. Another significant factor was the 'new' TCAS display limitation to +/- 2000' on visible traffic; so at the excessive rates of climb and descent we had no way of seeing any possible traffic conflicts. I was finally able to talk to and inform ATC after the whole event was over; getting a new altitude assignment. I did not note the pitch attitudes we passed through but when I called the Flight Attendants they did note an almost zero-G feeling and an unusual quiet in the aircraft during the upset recovery. They also reported no injury to themselves or any passengers. The FO did a superb job recovering from the upset while not exceeding G-limits; positive or negative; that might have overstressed the aircraft or caused an aerodynamic stall.This would have been difficult to avoid. There was a plot indicating possible MW (Mountain Wave) over the Sierras but all preceding traffic on our route reported smooth or light chop with no wave so it seemed safe to continue. I don't remember the height limit of the MW plot but I think we were going to be above it. We could have routed a lot further south to avoid the area.
The only thing that might have prevented this is a PIREP or SIGMET that would have indicated severe mountain wave. We knew that mountain wave had been reported but no idea how bad it was. I think it was good that we recognized what was happening early; the autopilot was already off; we hadn't reduced the thrust; and were anticipating a rapid and large loss of airspeed.
B737-800 flight crew reported an encounter with severe mountain wave that resulted in large altitude and airspeed excursions.