An M205 pilot was unable to maintain his altitude near dnw due to mountain wave activity.

Attributes
ACN	463805
Time
Date	200002
Day	Mon
Local Time Of Day	0601 To 1200
Place
State Reference	WY
Altitude	msl bound lower : 14500 msl bound upper : 15000
Environment
Flight Conditions	IMC
Weather Elements	Turbulence
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zlc.artcc
Operator	general aviation : personal
Make Model Name	M-20 Series Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zlc.artcc
Make Model Name	DC-3/Dakota/Skytrain
Flight Phase	cruise : level
Flight Plan	None
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 60 flight time total : 850 flight time type : 700
ASRS Report	463805
Person 2
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe inflight encounter : weather inflight encounter : turbulence non adherence : clearance other anomaly other anomaly other
Independent Detector	atc equipment : conflict alert other controllera other flight crewa
Resolutory Action	controller : issued new clearance controller : separated traffic flight crew : regained aircraft control
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Weather Flight Crew Human Performance
Primary Problem	Weather

Narrative:

Leaving jac assigned altitude after crossing dnw VOR, was 15000 ft MSL, direct sux. ATC approved a 360 degree turn to gain altitude before dnw and I crossed about 12000-13000 ft in a continued climb. I encountered severe turbulence just after dnw losing and gaining in excess of 700 ft. After regaining control of the plane, I continued climb to 15000 ft, but was unable to maintain altitude because of 'mountain wave.' after dropping to 14500 ft, ZLC needed to vector me south and a DC3 north of course to maintain separation. At that point, I believe both planes were in VFR conditions and I never made visual contact. I was told to call slc on landing and that person suggested that I report inability to hold altitude more promptly.

Original NASA ASRS Text

Title: AN M205 PLT WAS UNABLE TO MAINTAIN HIS ALT NEAR DNW DUE TO MOUNTAIN WAVE ACTIVITY.

Narrative: LEAVING JAC ASSIGNED ALT AFTER XING DNW VOR, WAS 15000 FT MSL, DIRECT SUX. ATC APPROVED A 360 DEG TURN TO GAIN ALT BEFORE DNW AND I CROSSED ABOUT 12000-13000 FT IN A CONTINUED CLB. I ENCOUNTERED SEVERE TURB JUST AFTER DNW LOSING AND GAINING IN EXCESS OF 700 FT. AFTER REGAINING CTL OF THE PLANE, I CONTINUED CLB TO 15000 FT, BUT WAS UNABLE TO MAINTAIN ALT BECAUSE OF 'MOUNTAIN WAVE.' AFTER DROPPING TO 14500 FT, ZLC NEEDED TO VECTOR ME S AND A DC3 N OF COURSE TO MAINTAIN SEPARATION. AT THAT POINT, I BELIEVE BOTH PLANES WERE IN VFR CONDITIONS AND I NEVER MADE VISUAL CONTACT. I WAS TOLD TO CALL SLC ON LNDG AND THAT PERSON SUGGESTED THAT I RPT INABILITY TO HOLD ALT MORE PROMPTLY.

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.