B777 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Total 14829; Flight Crew Type 1353
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Inflight Event / Encounter Weather / Turbulence
Flight Crew Returned To Clearance; General Maintenance Action
Weather
While level in cruise with the autopilot and autothrottles engaged in smooth air we were at FL370 cruising at M.833-.836. The autothrottles were stable. The aircraft started climbing; the autopilot started to nose over. I reached for the throttles and pulled them back as the aircraft started to accelerate. The autopilot nosed over more. I pulled the throttles to idle and shut the autothrottles off. The overspeed warning then sounded and I shut the autopilot off and applied slight back pressure to the yoke. At this point the aircraft was climbing and still accelerating. The speed went 30 knots into the barber pole before slowing and we climbed to FL373. We descended back to FL370. Reported the severe mountain wave to ATC of +/- 35 knots and +/- 300 feet altitude. We contacted Dispatch [and] told them of the severe mountain wave encounter and asked for a phone patch to [Maintenance] as this was a large overspeed we wanted to ensure that we were ok to continue. [Maintenance] told us we were ok and the aircraft would be inspected in [destination airport].
B777 Captain reported encountering severe mountain wave turbulence at FL370 that resulted in speed and altitude excursions.