C560XL experiences severe turbulence at FL390. No weather was detected by the weather radar.

Attributes
ACN	814368
Time
Date	200811
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : mia.airport
State Reference	FL
Altitude	msl single value : 39000
Environment
Flight Conditions	IMC
Weather Elements	Turbulence
Aircraft 1
Operator	general aviation : personal
Make Model Name	Citation V
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 50 flight time total : 7500 flight time type : 500
ASRS Report	814368
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : turbulence other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : regained aircraft control flight crew : exited adverse environment
Supplementary
Problem Areas	Environmental Factor Weather
Primary Problem	Environmental Factor

Narrative:

While in cruise flight at FL390; approximately 350 NM ssw of sby VOR (east of AR3; north of scoby intersection) my aircraft encountered a very localized area of severe turbulence. WX radar was on and showed no threats. At approximately 2-3 mi crew observed a vertical cloud formation in our path of flight. The cloud appeared to be between 1/4 and 1/2 mi in diameter and lacked definition. I disconnected the autoplt and entered a 15 degree left bank to avoid flying through the center of the column. As the right wing passed the outer edges of the cloud we experienced a roll upset of approximately 45 degrees left then right; immediately afterwards we encountered a severe downdraft resulting in a loss of approximately 1000 ft in approximately 10 seconds. With little pilot input the aircraft returned to FL390 almost immediately. We estimate the whole event to have lasted less than 45 seconds. During the descending portion of the encounter I was able to briefly report to center (miami; I think) that we were unable to maintain altitude due to severe turbulence; ATC acknowledged our report. Upon returning to FL390 we entered an area of VMC and smooth conditions. I can only conclude that as we passed a frontal boundary that we encountered the final stage of an imbedded thunderstorm that did not contain enough moisture to register on our radar.

Original NASA ASRS Text

Title: C560XL EXPERIENCES SEVERE TURBULENCE AT FL390. NO WEATHER WAS DETECTED BY THE WEATHER RADAR.

Narrative: WHILE IN CRUISE FLT AT FL390; APPROX 350 NM SSW OF SBY VOR (E OF AR3; N OF SCOBY INTXN) MY ACFT ENCOUNTERED A VERY LOCALIZED AREA OF SEVERE TURB. WX RADAR WAS ON AND SHOWED NO THREATS. AT APPROX 2-3 MI CREW OBSERVED A VERT CLOUD FORMATION IN OUR PATH OF FLT. THE CLOUD APPEARED TO BE BTWN 1/4 AND 1/2 MI IN DIAMETER AND LACKED DEFINITION. I DISCONNECTED THE AUTOPLT AND ENTERED A 15 DEG L BANK TO AVOID FLYING THROUGH THE CTR OF THE COLUMN. AS THE R WING PASSED THE OUTER EDGES OF THE CLOUD WE EXPERIENCED A ROLL UPSET OF APPROX 45 DEGS L THEN R; IMMEDIATELY AFTERWARDS WE ENCOUNTERED A SEVERE DOWNDRAFT RESULTING IN A LOSS OF APPROX 1000 FT IN APPROX 10 SECONDS. WITH LITTLE PLT INPUT THE ACFT RETURNED TO FL390 ALMOST IMMEDIATELY. WE ESTIMATE THE WHOLE EVENT TO HAVE LASTED LESS THAN 45 SECONDS. DURING THE DSNDING PORTION OF THE ENCOUNTER I WAS ABLE TO BRIEFLY RPT TO CTR (MIAMI; I THINK) THAT WE WERE UNABLE TO MAINTAIN ALT DUE TO SEVERE TURB; ATC ACKNOWLEDGED OUR RPT. UPON RETURNING TO FL390 WE ENTERED AN AREA OF VMC AND SMOOTH CONDITIONS. I CAN ONLY CONCLUDE THAT AS WE PASSED A FRONTAL BOUNDARY THAT WE ENCOUNTERED THE FINAL STAGE OF AN IMBEDDED TSTM THAT DID NOT CONTAIN ENOUGH MOISTURE TO REGISTER ON OUR RADAR.

Data retrieved from NASA's ASRS site as of May 2009 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.