Medium large transport excursion from assigned altitude due to mountain wave turbulence.

Attributes
ACN	298802
Time
Date	199503
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : rno
State Reference	NV
Altitude	msl bound lower : 25200 msl bound upper : 26000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zoa
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : commercial pilot : atp
Experience	flight time last 90 days : 180 flight time total : 15000 flight time type : 5000
ASRS Report	298802
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	other

Narrative:

Encountered sudden strong turbulence/mountain wave which exceeded autoplts capability resulting in disconnect. Aircraft was hand flown utilizing pitch control in attempting to maintain plus 16 degree flight. Airspeed fluctuated approximately 40 KIAS and vertical speeds of plus or minus 200 FPM were experienced. PNF notified ATC of probable altitude deviations and aircraft did descend to approximately 25200 ft during episode. Encounter lasted approximately 30 seconds. Radar was on/displayed, no returns. Seat belt sign off. Aft flight attendants were lifted off of floor but alighted gracefully. No ATC conflict/ no injuries/ some spilled drinks.

Original NASA ASRS Text

Title: MLG EXCURSION FROM ASSIGNED ALT DUE TO MOUNTAIN WAVE TURB.

Narrative: ENCOUNTERED SUDDEN STRONG TURB/MOUNTAIN WAVE WHICH EXCEEDED AUTOPLTS CAPABILITY RESULTING IN DISCONNECT. ACFT WAS HAND FLOWN UTILIZING PITCH CTL IN ATTEMPTING TO MAINTAIN PLUS 16 DEG FLT. AIRSPD FLUCTUATED APPROX 40 KIAS AND VERT SPDS OF PLUS OR MINUS 200 FPM WERE EXPERIENCED. PNF NOTIFIED ATC OF PROBABLE ALT DEVS AND ACFT DID DSND TO APPROX 25200 FT DURING EPISODE. ENCOUNTER LASTED APPROX 30 SECONDS. RADAR WAS ON/DISPLAYED, NO RETURNS. SEAT BELT SIGN OFF. AFT FLT ATTENDANTS WERE LIFTED OFF OF FLOOR BUT ALIGHTED GRACEFULLY. NO ATC CONFLICT/ NO INJURIES/ SOME SPILLED DRINKS.

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.