Narrative:

Mountain wave encounter: 2 locations: publication 245 at 20 nm and ALS 360 at 60 nm. Just west of publication heading west we encountered severe to extreme mountain wave conditions at FL380. This caused an overspeed; M.828; 268 kts for approximately 7-10 seconds. I corrected the overspeed and then shortly thereafter we lost 45-50 kts airspeed; going into the upper amber airspeed band and getting stick shaker at FL380. I began a descent to recover airspeed and told first officer to ask ATC for a lower altitude. ATC assigned us FL360. Very soon after leveling at FL360 we encountered moderate turbulence and airspeed again dropped into the upper amber band along with stick shaker. During stick shaker recovery more mountain wave caused increasing airspeed into an overspeed condition again and an altitude gain of about 1500 feet to FL372. I corrected for the overspeed and we requested FL340 from ATC. The seatbelt sign was on at least 4 minutes before the encounter and during the event and there were no injuries as reported to me from F/a #1.I believe our flight was the first flight that morning to encounter severe to extreme mountain wave at FL380 or any altitude. There were no PIREP reports about this severe to extreme mountain wave. We were filed M.80 at FL380. I believe we were at M.78 because I had slowed a couple of minutes earlier due to some light turbulence. I don't think the overspeed would have been avoided had we been at cost index 0 mach (exactly midway between upper band and lower band). The only way I can think of to avoid recurrence would be to know about this extreme mountain wave and then deviate around it but we did not know about it and neither did ATC or our dispatcher.

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Original NASA ASRS Text

Title: B737-800 flight crew reported airspeed and altitude excursions resulted from two encounters with extreme mountain waves crossing the Rocky Mountains in the vicinity of PUB and ALS.

Narrative: Mountain Wave Encounter: 2 Locations: PUB 245 at 20 nm and ALS 360 at 60 nm. Just west of PUB heading west we encountered severe to extreme mountain wave conditions at FL380. This caused an overspeed; M.828; 268 kts for approximately 7-10 seconds. I corrected the overspeed and then shortly thereafter we lost 45-50 kts airspeed; going into the upper amber airspeed band and getting stick shaker at FL380. I began a descent to recover airspeed and told FO to ask ATC for a lower altitude. ATC assigned us FL360. Very soon after leveling at FL360 we encountered moderate turbulence and airspeed again dropped into the upper amber band along with stick shaker. During stick shaker recovery more mountain wave caused increasing airspeed into an overspeed condition again and an altitude gain of about 1500 feet to FL372. I corrected for the overspeed and we requested FL340 from ATC. The Seatbelt Sign was on at least 4 minutes before the encounter and during the event and there were no injuries as reported to me from F/A #1.I believe our flight was the first flight that morning to encounter severe to extreme mountain wave at FL380 or any altitude. There were no PIREP reports about this severe to extreme mountain wave. We were filed M.80 at FL380. I believe we were at M.78 because I had slowed a couple of minutes earlier due to some light turbulence. I don't think the overspeed would have been avoided had we been at cost index 0 Mach (exactly midway between upper band and lower band). The only way I can think of to avoid recurrence would be to know about this extreme mountain wave and then deviate around it but we did not know about it and neither did ATC or our dispatcher.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.