Air carrier flight encountered mountain wave activity. Altitude deviation altitude excursion.

Attributes
ACN	319130
Time
Date	199510
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : jnc
State Reference	CO
Altitude	msl bound lower : 34400 msl bound upper : 35000
Environment
Flight Conditions	Mixed
Light	Night
Aircraft 1
Controlling Facilities	artcc : zdv
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 cruise other
Route In Use	enroute other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 200 flight time total : 18000 flight time type : 1100
ASRS Report	319130
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Experience	flight time last 90 days : 200 flight time total : 6500 flight time type : 3000
ASRS Report	318382
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather inflight encounter other non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	other

Narrative:

While flying at FL350 in the area of a frontal system, we were experiencing light to moderate chop, skimming the top of a cloud layer, thunderstorm activity to the south and north of route. We were deviating around the tops of some storms and encountered some mountain wave activity. The autoplt was engaged and aircraft started up, then pitched down at 4000 FPM indication on ivsi. We lost 600 ft and aircraft pitched up at 2500 FPM indication on ivsi. I assisted autoplt recovery to FL350. We reported to ATC that we had encountered severe mountain wave.

Original NASA ASRS Text

Title: ACR FLT ENCOUNTERED MOUNTAIN WAVE ACTIVITY. ALTDEV ALT EXCURSION.

Narrative: WHILE FLYING AT FL350 IN THE AREA OF A FRONTAL SYS, WE WERE EXPERIENCING LIGHT TO MODERATE CHOP, SKIMMING THE TOP OF A CLOUD LAYER, TSTM ACTIVITY TO THE S AND N OF RTE. WE WERE DEVIATING AROUND THE TOPS OF SOME STORMS AND ENCOUNTERED SOME MOUNTAIN WAVE ACTIVITY. THE AUTOPLT WAS ENGAGED AND ACFT STARTED UP, THEN PITCHED DOWN AT 4000 FPM INDICATION ON IVSI. WE LOST 600 FT AND ACFT PITCHED UP AT 2500 FPM INDICATION ON IVSI. I ASSISTED AUTOPLT RECOVERY TO FL350. WE RPTED TO ATC THAT WE HAD ENCOUNTERED SEVERE MOUNTAIN WAVE.

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.