C182 pilot was unable to maintain altitude due to mountain wave in ZDV airspace.

Attributes
ACN	403472
Time
Date	199805
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : cim
State Reference	NM
Altitude	msl bound lower : 9700 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	general aviation : personal
Make Model Name	Skylane 182/RG Turbo Skylane/RG
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Route In Use	enroute airway : zdv
Flight Plan	IFR
Aircraft 2
Make Model Name	Skylane 182/RG Turbo Skylane/RG
Person 1
Affiliation	Other
Function	oversight : pic
Qualification	pilot : commercial pilot : instrument
Experience	flight time last 90 days : 20 flight time total : 1780 flight time type : 1750
ASRS Report	403472
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter other non adherence : clearance other anomaly other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : declared emergency flight crew : exited adverse environment
Consequence	Other
Supplementary
Primary Problem	Weather

Narrative:

While northbound approximately 30 NM from cimarron VOR, on V-19, in cruise flight, I encountered a strong downdraft. I was forced to configure the aircraft to vx to maintain altitude but eventually this failed and after approximately 8 NM I was unable to maintain altitude. I requested a block assignment of 11000- 12000 ft but was unable to maintain this. I requested a deviation towards lower terrain at trinidad, co. I was able to halt the descent at 9700 ft MSL which is below MEA/MOCA for this segment. I was able to initiate a climb at vy approximately 12 mi southwest of trinidad and eventually was able to return to my assigned altitude. I estimate the downward portion of this wave was approximately 30 mi north to south and 15 mi east to west. At the time of the incident the aircraft was in the forward third of the weight/balance envelope and approximately 500 pounds below gross weight. Winds aloft at my altitude were approximately 240 degrees at 15 KTS which was close to forecast. There were no airmets in effect for this route and only the usual light turbulence had been encountered. Forecast winds over the mountain peaks was 20-22 KTS for northern new mexico and southern colorado. Rate of sink at vx averaged -150 FPM with range of 0 to -600 FPM.

Original NASA ASRS Text

Title: C182 PLT WAS UNABLE TO MAINTAIN ALT DUE TO MOUNTAIN WAVE IN ZDV AIRSPACE.

Narrative: WHILE NBOUND APPROX 30 NM FROM CIMARRON VOR, ON V-19, IN CRUISE FLT, I ENCOUNTERED A STRONG DOWNDRAFT. I WAS FORCED TO CONFIGURE THE ACFT TO VX TO MAINTAIN ALT BUT EVENTUALLY THIS FAILED AND AFTER APPROX 8 NM I WAS UNABLE TO MAINTAIN ALT. I REQUESTED A BLOCK ASSIGNMENT OF 11000- 12000 FT BUT WAS UNABLE TO MAINTAIN THIS. I REQUESTED A DEV TOWARDS LOWER TERRAIN AT TRINIDAD, CO. I WAS ABLE TO HALT THE DSCNT AT 9700 FT MSL WHICH IS BELOW MEA/MOCA FOR THIS SEGMENT. I WAS ABLE TO INITIATE A CLB AT VY APPROX 12 MI SW OF TRINIDAD AND EVENTUALLY WAS ABLE TO RETURN TO MY ASSIGNED ALT. I ESTIMATE THE DOWNWARD PORTION OF THIS WAVE WAS APPROX 30 MI N TO S AND 15 MI E TO W. AT THE TIME OF THE INCIDENT THE ACFT WAS IN THE FORWARD THIRD OF THE WT/BAL ENVELOPE AND APPROX 500 LBS BELOW GROSS WT. WINDS ALOFT AT MY ALT WERE APPROX 240 DEGS AT 15 KTS WHICH WAS CLOSE TO FORECAST. THERE WERE NO AIRMETS IN EFFECT FOR THIS RTE AND ONLY THE USUAL LIGHT TURB HAD BEEN ENCOUNTERED. FORECAST WINDS OVER THE MOUNTAIN PEAKS WAS 20-22 KTS FOR NORTHERN NEW MEXICO AND SOUTHERN COLORADO. RATE OF SINK AT VX AVERAGED -150 FPM WITH RANGE OF 0 TO -600 FPM.

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.