B787 Dreamliner Undifferentiated or Other Model
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 158; Flight Crew Total 11316; Flight Crew Type 6504
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Flight Crew Regained Aircraft Control
Weather
At FL380; in smooth air; we encountered a sudden non-mountainous wave. We encountered fluctuations in speed up to plus and minus 25 knots (roughly M88 to M78) and altitude deviations of up to 300-400 feet. Rates of climb and descent reached 1800 feet per minute. Event lasted for about a minute before we descended with clearance to FL360. The aircraft over speed was probably by a few knots; but not over 5 knots.
Air Carrier Flight Crew reported a sudden non-mountainous wave activity in cruise.