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When a B737-800 encountered a mountain wave at FL390 the airspeed exceeded vmo/mmo by 12 knots for 5-7 seconds and the aircraft climbed nearly 500 ft so the aircraft thrust levers were retarded while the speed brakes were extended.
| Attributes | |
| ACN | 929312 |
| Time | |
| Date | 201101 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ZDV.ARTCC |
| State Reference | CO |
| Environment | |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B737-800 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Cruise |
| Flight Plan | IFR |
| Person 1 | |
| Function | Captain Pilot Not Flying |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Events | |
| Anomaly | Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy Deviation - Speed All Types Inflight Event / Encounter Weather / Turbulence |
Narrative:
Encountered a moderate mountain wave while at cruise. We were level at fl 390 at .77M/246 KIAS. Aircraft rapidly accelerated through vmo/mmo by approximately 12 KIAS for 5-7 seconds. Thrust levers were retarded and speed brakes carefully deployed to arrest acceleration. Additionally; aircraft gained almost 500 ft in altitude. The autopilot had been engaged when the event occurred.
Original NASA ASRS Text
Title: When a B737-800 encountered a mountain wave at FL390 the airspeed exceeded VMO/MMO by 12 knots for 5-7 seconds and the aircraft climbed nearly 500 FT so the aircraft thrust levers were retarded while the speed brakes were extended.
Narrative: Encountered a moderate mountain wave while at cruise. We were level at FL 390 at .77M/246 KIAS. Aircraft rapidly accelerated through VMO/MMO by approximately 12 KIAS for 5-7 seconds. Thrust levers were retarded and speed brakes carefully deployed to arrest acceleration. Additionally; aircraft gained almost 500 FT in altitude. The autopilot had been engaged when the event occurred.
Data retrieved from NASA's ASRS site as of April 2012 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.