IFR TMB7 at FL180 was unable to maintain assigned altitude because of turbulence.

Attributes
ACN	588051
Time
Date	200307
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	intersection : powdr
State Reference	CO
Altitude	msl single value : 18000
Environment
Flight Conditions	IMC
Weather Elements	Rain Thunderstorm Turbulence Windshear other
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv.artcc tower : zzz.tower
Operator	general aviation : personal
Make Model Name	TBM 700
Operating Under FAR Part	Part 91
Flight Phase	descent : intermediate altitude
Route In Use	arrival star : thompson 5
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zdv.artcc
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : private pilot : multi engine pilot : instrument
Experience	flight time last 90 days : 46.1 flight time total : 1236 flight time type : 160
ASRS Report	588051
Person 2
Function	flight crew : captain oversight : pic
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe inflight encounter : turbulence inflight encounter : weather non adherence : clearance non adherence : required legal separation other anomaly
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued alert flight crew : exited adverse environment flight crew : returned to assigned altitude
Consequence	faa : investigated faa : reviewed incident with flight crew
Supplementary
Problem Areas	Weather Flight Crew Human Performance
Primary Problem	Weather
Air Traffic Incident	Operational Error

Narrative:

My flight originated in santa monica, ca, with a destination of jefferson country airport, co. Scattered to widely scattered thunderstorms with tops to FL450, with lower cumulo form clouds with tops to FL300, required deviations left and right off course, beginning in south central utah and continuing into denver area. In the vicinity of aspen, co (ase), at FL290, I was cleared to bjc via 'direct powdr intersection thomson five arrival.' as ATC began to step me down, deviations around buildups and areas of heavier precipitation were required almost constantly. I was relying on radar on board, as well as storm scope. As I descended through FL240, I was in and out of IMC, in moderate turbulence. The radar was showing wide areas of moderate precipitation, but no lightning. While deviating right off course and leveling at FL180, I entered a cloud whose top appeared to be in the high 20's (ft), and whose base appeared to be 1000-2000 ft below me. Immediately upon entering IMC again, I entered moderate-to-severe turbulence, very heavy precipitation (rain or possibly hail), my autoplt disconnected, and the vertical speed indictor showed a descent rate in excess of 2500 FPM. I applied full throttle (I had previously slowed the plane down to my turbulent air penetration speed of 158 KIAS) in an attempt to climb back up to my assigned altitude of FL180. When I was unable to immediately get a positive rate of climb, I asked the controller 'for lower altitude.' he ordered me to maintain FL180, and within a few seconds I began to exit the heaviest precipitation and climb back up to 18000 ft MSL. According to the denver approach controller, a loss of separation had occurred. I believe that the intensity of the rain in the cumulus cloud I entered had caused the windshear or downdraft I was caught in. Had I been able to maintain VMC, I would have seen the heavy downpour, and would have avoided the cloud altogether. However, my altitude placed me right in the midst of an area of clouds and precipitation, and maintaining VMC was not possible.

Original NASA ASRS Text

Title: IFR TMB7 AT FL180 WAS UNABLE TO MAINTAIN ASSIGNED ALT BECAUSE OF TURB.

Narrative: MY FLT ORIGINATED IN SANTA MONICA, CA, WITH A DEST OF JEFFERSON COUNTRY ARPT, CO. SCATTERED TO WIDELY SCATTERED TSTMS WITH TOPS TO FL450, WITH LOWER CUMULO FORM CLOUDS WITH TOPS TO FL300, REQUIRED DEVS L AND R OFF COURSE, BEGINNING IN S CENTRAL UTAH AND CONTINUING INTO DENVER AREA. IN THE VICINITY OF ASPEN, CO (ASE), AT FL290, I WAS CLRED TO BJC VIA 'DIRECT POWDR INTXN THOMSON FIVE ARR.' AS ATC BEGAN TO STEP ME DOWN, DEVS AROUND BUILDUPS AND AREAS OF HEAVIER PRECIPITATION WERE REQUIRED ALMOST CONSTANTLY. I WAS RELYING ON RADAR ON BOARD, AS WELL AS STORM SCOPE. AS I DSNDED THROUGH FL240, I WAS IN AND OUT OF IMC, IN MODERATE TURB. THE RADAR WAS SHOWING WIDE AREAS OF MODERATE PRECIPITATION, BUT NO LIGHTNING. WHILE DEVIATING R OFF COURSE AND LEVELING AT FL180, I ENTERED A CLOUD WHOSE TOP APPEARED TO BE IN THE HIGH 20'S (FT), AND WHOSE BASE APPEARED TO BE 1000-2000 FT BELOW ME. IMMEDIATELY UPON ENTERING IMC AGAIN, I ENTERED MODERATE-TO-SEVERE TURB, VERY HVY PRECIPITATION (RAIN OR POSSIBLY HAIL), MY AUTOPLT DISCONNECTED, AND THE VERT SPD INDICTOR SHOWED A DSCNT RATE IN EXCESS OF 2500 FPM. I APPLIED FULL THROTTLE (I HAD PREVIOUSLY SLOWED THE PLANE DOWN TO MY TURBULENT AIR PENETRATION SPD OF 158 KIAS) IN AN ATTEMPT TO CLB BACK UP TO MY ASSIGNED ALT OF FL180. WHEN I WAS UNABLE TO IMMEDIATELY GET A POSITIVE RATE OF CLB, I ASKED THE CTLR 'FOR LOWER ALT.' HE ORDERED ME TO MAINTAIN FL180, AND WITHIN A FEW SECONDS I BEGAN TO EXIT THE HEAVIEST PRECIPITATION AND CLB BACK UP TO 18000 FT MSL. ACCORDING TO THE DENVER APCH CTLR, A LOSS OF SEPARATION HAD OCCURRED. I BELIEVE THAT THE INTENSITY OF THE RAIN IN THE CUMULUS CLOUD I ENTERED HAD CAUSED THE WINDSHEAR OR DOWNDRAFT I WAS CAUGHT IN. HAD I BEEN ABLE TO MAINTAIN VMC, I WOULD HAVE SEEN THE HVY DOWNPOUR, AND WOULD HAVE AVOIDED THE CLOUD ALTOGETHER. HOWEVER, MY ALT PLACED ME RIGHT IN THE MIDST OF AN AREA OF CLOUDS AND PRECIPITATION, AND MAINTAINING VMC WAS NOT POSSIBLE.

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.