Narrative:

While approximately 50 mi west of denver, co, at FL330, we encountered a mountain wave phenomenon. We were cruising at mach 80 with the autoplt on (approximately IAS 282 KTS). The initial indication was an increase in airspeed beyond vmo/mmo. The aircraft started a rapid descent with the autoplt on (little change in aircraft attitude). Within 2-3 seconds after the aircraft started an altitude loss, the autoplt kicked off by itself. At this time I disconnected the autothrottles and started to retard the throttles idle to control the airspeed while raising the nose of the aircraft 2-3 degrees. The aircraft had lost approximately 1500-2000' in less than 30 second (vsi was pegged at 6000 FPM descent). Then the aircraft started a climb (aircraft attitude was very close to level flight attitude). Airspeed started to decrease and vsi showed a high climb rate. Airspeed started to decay and decayed below vls. As the aircraft passed through 34000' the captain requested FL350 from denver center. The captain reported the mountain wave action to denver center. The controller who was controling us stated he was getting large altitude flutuations on his altitude readout, and he would make a note of this occurrence. The entire occurrence was less then 90 seconds however, I felt at times we had no control over the situation and were just along for the ride.

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Original NASA ASRS Text

Title: ACR WDB 3000' ALT DEVIATION AND SPEED DEVIATION IN MOUNTAIN WAVE 50 WEST OF DEN AT NIGHT.

Narrative: WHILE APPROX 50 MI W OF DENVER, CO, AT FL330, WE ENCOUNTERED A MOUNTAIN WAVE PHENOMENON. WE WERE CRUISING AT MACH 80 WITH THE AUTOPLT ON (APPROX IAS 282 KTS). THE INITIAL INDICATION WAS AN INCREASE IN AIRSPD BEYOND VMO/MMO. THE ACFT STARTED A RAPID DSNT WITH THE AUTOPLT ON (LITTLE CHANGE IN ACFT ATTITUDE). WITHIN 2-3 SECS AFTER THE ACFT STARTED AN ALT LOSS, THE AUTOPLT KICKED OFF BY ITSELF. AT THIS TIME I DISCONNECTED THE AUTOTHROTTLES AND STARTED TO RETARD THE THROTTLES IDLE TO CTL THE AIRSPD WHILE RAISING THE NOSE OF THE ACFT 2-3 DEGS. THE ACFT HAD LOST APPROX 1500-2000' IN LESS THAN 30 SEC (VSI WAS PEGGED AT 6000 FPM DSNT). THEN THE ACFT STARTED A CLB (ACFT ATTITUDE WAS VERY CLOSE TO LEVEL FLT ATTITUDE). AIRSPD STARTED TO DECREASE AND VSI SHOWED A HIGH CLB RATE. AIRSPD STARTED TO DECAY AND DECAYED BELOW VLS. AS THE ACFT PASSED THROUGH 34000' THE CAPT REQUESTED FL350 FROM DENVER CTR. THE CAPT RPTED THE MOUNTAIN WAVE ACTION TO DENVER CTR. THE CTLR WHO WAS CTLING US STATED HE WAS GETTING LARGE ALT FLUTUATIONS ON HIS ALT READOUT, AND HE WOULD MAKE A NOTE OF THIS OCCURRENCE. THE ENTIRE OCCURRENCE WAS LESS THEN 90 SECS HOWEVER, I FELT AT TIMES WE HAD NO CTL OVER THE SITUATION AND WERE JUST ALONG FOR THE RIDE.

Data retrieved from NASA's ASRS site as of July 2007 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.