A B757 experience moderate to severe mountain wave action over the central sierra nevada mountains a...

Attributes
ACN	950797
Time
Date	201105
Local Time Of Day	1201-1800
Place
Locale Reference	ZOA.ARTCC
State Reference	CA
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	First Officer Pilot Flying
Experience	Flight Crew Last 90 Days 150 Flight Crew Total 8000 Flight Crew Type 5000
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Inflight Event / Encounter Weather / Turbulence

Narrative:

Upon initial check in with ZOA we were advised of continuous to moderate chop and moderate mountain wave action at all altitudes. While at FL340; doing .79 mach we experienced moderate to severe mountain wave action. Over the central sierra nevada mountains the airspeed immediately jumped up to .84 mach and we hit a descending mountain wave exceeding 1;000 FPM. I immediately retarded the throttles and the captain selected 'continuous' on the engine start selectors due to the turbulence. The aircraft descended approximately 330 ft. The captain advised ATC we were unable to maintain FL340 due to the mountain wave and stated our current altitude of FL337. The controller then gave us a descent to FL260. The wave subsided but we were still in moderate turbulence to chop. This all occurred in a matter of a few seconds. I feel there was nothing we could have done to preclude this from happening. We were in a descending air mass of over 1;000 FPM.

Original NASA ASRS Text

Title: A B757 experience moderate to severe mountain wave action over the central Sierra Nevada mountains at FL340. ATC cleared them to FL260 and into moderate chop to light turbulence.

Narrative: Upon initial check in with ZOA we were advised of continuous to moderate chop and moderate mountain wave action at all altitudes. While at FL340; doing .79 MACH we experienced moderate to severe mountain wave action. Over the central Sierra Nevada mountains the airspeed immediately jumped up to .84 mach and we hit a descending mountain wave exceeding 1;000 FPM. I immediately retarded the throttles and the Captain selected 'continuous' on the Engine Start Selectors due to the turbulence. The aircraft descended approximately 330 FT. The Captain advised ATC we were unable to maintain FL340 due to the mountain wave and stated our current altitude of FL337. The Controller then gave us a descent to FL260. The wave subsided but we were still in moderate turbulence to chop. This all occurred in a matter of a few seconds. I feel there was nothing we could have done to preclude this from happening. We were in a descending air mass of over 1;000 FPM.

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.

A B757 experience moderate to severe mountain wave action over the central sierra nevada mountains at FL340. ATC cleared them to FL260 and into moderate chop to light turbulence.