Narrative:

Cruising at FL410 near great falls. I was PF and flying on autoplt. Encountered unrpted moderate to severe mountain wave, worst that I had ever experienced. Airspeed dropped off abruptly, added power and airspeed immediately accelerated to (and past) barber pole. Took autoplt off, and retarded throttles. Airspeed dropped precipitously. During this evolution, pitch attitudes were varying between 3 degrees nose down and 7 degrees nose up in an attempt to maintain FL410. Keeping within these parameters required very aggressive pitch movement. During this time, actual indicated altitude varied between FL408 and FL413.5. Mach varied between .78 mach and .88 mach, although the so thought that he saw much slower. As engines were spooling down in response to retarding throttles, airspeed dropped quickly and throttles were advanced. Engine #1 experienced a stall condition and would not respond to throttle input in either direction. Captain immediately reported the mountain wave, almost simultaneously with 2 other aircraft reporting same. When engine #1 would not accelerate (it had stalled at idle), captain immediately asked for lower altitude. Initially assigned FL370. Approaching FL370, engine still was not responding, so asked for lower still. Assigned FL330. During descent, #1 throttle left at idle. Leveling off at FL330, attempted to advance throttle and accelerate engine. Engine began to respond normally. Flight continued uneventfully to msp. Crew wrote up logbook entry, and filed out engine operation report. No injuries in cabin during episode.

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Original NASA ASRS Text

Title: B747-200 CREW ENCOUNTERED SEVERE MOUNTAIN WAVE ACTIVITY NEAR GRF IN ZLC CLASS A AIRSPACE.

Narrative: CRUISING AT FL410 NEAR GREAT FALLS. I WAS PF AND FLYING ON AUTOPLT. ENCOUNTERED UNRPTED MODERATE TO SEVERE MOUNTAIN WAVE, WORST THAT I HAD EVER EXPERIENCED. AIRSPD DROPPED OFF ABRUPTLY, ADDED PWR AND AIRSPD IMMEDIATELY ACCELERATED TO (AND PAST) BARBER POLE. TOOK AUTOPLT OFF, AND RETARDED THROTTLES. AIRSPD DROPPED PRECIPITOUSLY. DURING THIS EVOLUTION, PITCH ATTITUDES WERE VARYING BTWN 3 DEGS NOSE DOWN AND 7 DEGS NOSE UP IN AN ATTEMPT TO MAINTAIN FL410. KEEPING WITHIN THESE PARAMETERS REQUIRED VERY AGGRESSIVE PITCH MOVEMENT. DURING THIS TIME, ACTUAL INDICATED ALT VARIED BTWN FL408 AND FL413.5. MACH VARIED BTWN .78 MACH AND .88 MACH, ALTHOUGH THE SO THOUGHT THAT HE SAW MUCH SLOWER. AS ENGS WERE SPOOLING DOWN IN RESPONSE TO RETARDING THROTTLES, AIRSPD DROPPED QUICKLY AND THROTTLES WERE ADVANCED. ENG #1 EXPERIENCED A STALL CONDITION AND WOULD NOT RESPOND TO THROTTLE INPUT IN EITHER DIRECTION. CAPT IMMEDIATELY RPTED THE MOUNTAIN WAVE, ALMOST SIMULTANEOUSLY WITH 2 OTHER ACFT RPTING SAME. WHEN ENG #1 WOULD NOT ACCELERATE (IT HAD STALLED AT IDLE), CAPT IMMEDIATELY ASKED FOR LOWER ALT. INITIALLY ASSIGNED FL370. APCHING FL370, ENG STILL WAS NOT RESPONDING, SO ASKED FOR LOWER STILL. ASSIGNED FL330. DURING DSCNT, #1 THROTTLE LEFT AT IDLE. LEVELING OFF AT FL330, ATTEMPTED TO ADVANCE THROTTLE AND ACCELERATE ENG. ENG BEGAN TO RESPOND NORMALLY. FLT CONTINUED UNEVENTFULLY TO MSP. CREW WROTE UP LOGBOOK ENTRY, AND FILED OUT ENG OP RPT. NO INJURIES IN CABIN DURING EPISODE.

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.