A B727 captain described his encounter with severe turbulence in the vicinity of bvt.

Attributes
ACN	482430
Time
Date	200008
Day	Thu
Local Time Of Day	1801 To 2400
Place
State Reference	IN
Altitude	msl bound lower : 30200 msl bound upper : 31800
Environment
Flight Conditions	IMC
Weather Elements	Turbulence Thunderstorm
Light	Night
Aircraft 1
Controlling Facilities	artcc : zau.artcc artcc : zab.artcc
Operator	common carrier : air carrier
Make Model Name	B727 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : atp
Experience	flight time last 90 days : 25 flight time total : 6050 flight time type : 360
ASRS Report	482430
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : turbulence inflight encounter : weather other anomaly
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : regained aircraft control
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Weather
Primary Problem	Weather

Narrative:

B727 encountered severe turbulence at FL310 en route from sdf to rfd. Our route of flight was sdf-iiu-V53-strep-bvt-edn-dpa-rfd. There were convective sigmets issued for our route of flight and we deviated around WX as necessary to remain clear of the thunderstorms. We were IMC at FL310, slowed to 280 KIAS for light turbulence we were encountering and the autoplt was engaged. The aircraft encountered severe turbulence about 35 mi west of bvt VOR at this flight level and speed. The aircraft gained and lost approximately 700-800 ft within 5-7 seconds. The crew and the aircraft experienced vertical loads of 2.5G to -1.0G. The autoplt disconnected itself automatically and aircraft recovery was made by the captain. We remained in severe turbulence for about 2-3 mins experiencing the same gain and loss of altitude and vertical loads for the same amount of time. ATC was advised of our situation of encountering the severe turbulence. We continued to deviate around WX for another 45 mi (65 mi northeast of bvt) then proceeded directly to rfd. The rest of the flight was uneventful. The WX radar was not painting (displaying) any WX on the screen when we encountered the severe turbulence.

Original NASA ASRS Text

Title: A B727 CAPT DESCRIBED HIS ENCOUNTER WITH SEVERE TURB IN THE VICINITY OF BVT.

Narrative: B727 ENCOUNTERED SEVERE TURB AT FL310 ENRTE FROM SDF TO RFD. OUR RTE OF FLT WAS SDF-IIU-V53-STREP-BVT-EDN-DPA-RFD. THERE WERE CONVECTIVE SIGMETS ISSUED FOR OUR RTE OF FLT AND WE DEVIATED AROUND WX AS NECESSARY TO REMAIN CLR OF THE TSTMS. WE WERE IMC AT FL310, SLOWED TO 280 KIAS FOR LIGHT TURB WE WERE ENCOUNTERING AND THE AUTOPLT WAS ENGAGED. THE ACFT ENCOUNTERED SEVERE TURB ABOUT 35 MI W OF BVT VOR AT THIS FLT LEVEL AND SPD. THE ACFT GAINED AND LOST APPROX 700-800 FT WITHIN 5-7 SECONDS. THE CREW AND THE ACFT EXPERIENCED VERT LOADS OF 2.5G TO -1.0G. THE AUTOPLT DISCONNECTED ITSELF AUTOMATICALLY AND ACFT RECOVERY WAS MADE BY THE CAPT. WE REMAINED IN SEVERE TURB FOR ABOUT 2-3 MINS EXPERIENCING THE SAME GAIN AND LOSS OF ALT AND VERT LOADS FOR THE SAME AMOUNT OF TIME. ATC WAS ADVISED OF OUR SIT OF ENCOUNTERING THE SEVERE TURB. WE CONTINUED TO DEVIATE AROUND WX FOR ANOTHER 45 MI (65 MI NE OF BVT) THEN PROCEEDED DIRECTLY TO RFD. THE REST OF THE FLT WAS UNEVENTFUL. THE WX RADAR WAS NOT PAINTING (DISPLAYING) ANY WX ON THE SCREEN WHEN WE ENCOUNTERED THE SEVERE TURB.

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.