An small aircraft deviated from its altitude during thunderstorm activity.

Attributes
ACN	222183
Time
Date	199209
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : mld
State Reference	ID
Altitude	msl bound lower : 12000 msl bound upper : 13000
Environment
Flight Conditions	IMC
Light	Dusk
Aircraft 1
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Retractable Gear
Flight Phase	cruise other
Route In Use	enroute : on vectors enroute airway : zlc
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : instrument
Experience	flight time last 90 days : 20 flight time total : 650 flight time type : 100
ASRS Report	222183
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance other anomaly
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course flight crew : regained aircraft control
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	Pilot Deviation

Narrative:

After having penetrated a thunderstorm for approximately 5 min, I encountered moderate-severe turbulence IMC, hard enough to hit my head on the ceiling of the aircraft. I immediately asked center for vectors to the nearest airport, still encountering turbulence. Once I was back in the clear, I noticed I had lost 1000 ft altitude from my assigned altitude of 13000. Although flight watch had reported severe thunderstorms in the vicinity, no lightning was visible, nor did the stormscope show any activity ahead. Furthermore, the line of thunderstorms was only 20 mi wide as reported. Altitude loss was probably due to a combination of power reduction to obtain va as fast as possible, downdrafts, and to the fact that I had my hands full keeping the plane controled in the turbulence and in IMC. Corrective action: once I discovered the altitude loss, I immediately started to climb. At about the same time, ATC cleared me to 11000. To prevent this occurrence, if WX says there is a severe circuit breaker in your path, believe them!

Original NASA ASRS Text

Title: AN SMA DEVIATED FROM ITS ALT DURING TSTM ACTIVITY.

Narrative: AFTER HAVING PENETRATED A TSTM FOR APPROX 5 MIN, I ENCOUNTERED MODERATE-SEVERE TURB IMC, HARD ENOUGH TO HIT MY HEAD ON THE CEILING OF THE ACFT. I IMMEDIATELY ASKED CTR FOR VECTORS TO THE NEAREST ARPT, STILL ENCOUNTERING TURB. ONCE I WAS BACK IN THE CLR, I NOTICED I HAD LOST 1000 FT ALT FROM MY ASSIGNED ALT OF 13000. ALTHOUGH FLT WATCH HAD RPTED SEVERE TSTMS IN THE VICINITY, NO LIGHTNING WAS VISIBLE, NOR DID THE STORMSCOPE SHOW ANY ACTIVITY AHEAD. FURTHERMORE, THE LINE OF TSTMS WAS ONLY 20 MI WIDE AS RPTED. ALT LOSS WAS PROBABLY DUE TO A COMBINATION OF PWR REDUCTION TO OBTAIN VA AS FAST AS POSSIBLE, DOWNDRAFTS, AND TO THE FACT THAT I HAD MY HANDS FULL KEEPING THE PLANE CTLED IN THE TURB AND IN IMC. CORRECTIVE ACTION: ONCE I DISCOVERED THE ALT LOSS, I IMMEDIATELY STARTED TO CLB. AT ABOUT THE SAME TIME, ATC CLRED ME TO 11000. TO PREVENT THIS OCCURRENCE, IF WX SAYS THERE IS A SEVERE CB IN YOUR PATH, BELIEVE THEM!

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.