A B737-300 encountered severe turbulence for 10-20 second. Aircraft control lost with airspeed deviation and a 1250 ft altitude loss at FL370.

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Attributes
ACN	784056
Time
Date	200804
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 37000
Environment
Weather Elements	Turbulence
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 42 flight time total : 6000 flight time type : 1000
ASRS Report	784056
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 90 flight time total : 12000 flight time type : 5000
ASRS Report	784052
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : turbulence other anomaly other anomaly
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : regained aircraft control flight crew : exited adverse environment flight crew : returned to original clearance
Supplementary
Problem Areas	Environmental Factor
Primary Problem	Environmental Factor

Narrative:

Stable cruise FL370 after leaving an area of numerous thunderstorms and light to moderate turbulence entered an area of isolated thunderstorms and just occasional light chop. WX radar selected both sides with no returns on our route of flight. With no warning; ie; wind shift or temperature variation; encountered an area of severe turbulence that the autoplt was unable to compensate for. Disengaged the autoplt/autothrottle and performed an unusual attitude recovery. Autoplt on for maybe 3 seconds of the turbulence; total duration of the turbulence somewhere between 10-20 seconds. Wings stayed fairly level; nose dropped to 2.5 - 5 degrees nose low with an associated increase in airspeed. Momentary high speed clacker; maybe 2 seconds; loss of 1000-1250 ft altitude; unable to recall vsi. Regained control of aircraft; climbed back to FL370 and reported severe turbulence and deviation to center. Center stated no paperwork necessary but better safe than sorry. Seatbelt sign was off but no passenger up at the time of incident. No injuries reported. Flight continued uneventfully.

Original NASA ASRS Text

Title: A B737-300 ENCOUNTERED SEVERE TURB FOR 10-20 SEC. ACFT CTL LOST WITH AIRSPEED DEV AND A 1250 FT ALT LOSS AT FL370.

Narrative: STABLE CRUISE FL370 AFTER LEAVING AN AREA OF NUMEROUS TSTMS AND LIGHT TO MODERATE TURB ENTERED AN AREA OF ISOLATED TSTMS AND JUST OCCASIONAL LIGHT CHOP. WX RADAR SELECTED BOTH SIDES WITH NO RETURNS ON OUR RTE OF FLT. WITH NO WARNING; IE; WIND SHIFT OR TEMP VARIATION; ENCOUNTERED AN AREA OF SEVERE TURB THAT THE AUTOPLT WAS UNABLE TO COMPENSATE FOR. DISENGAGED THE AUTOPLT/AUTOTHROTTLE AND PERFORMED AN UNUSUAL ATTITUDE RECOVERY. AUTOPLT ON FOR MAYBE 3 SECONDS OF THE TURB; TOTAL DURATION OF THE TURB SOMEWHERE BTWN 10-20 SECONDS. WINGS STAYED FAIRLY LEVEL; NOSE DROPPED TO 2.5 - 5 DEGS NOSE LOW WITH AN ASSOCIATED INCREASE IN AIRSPD. MOMENTARY HIGH SPD CLACKER; MAYBE 2 SECONDS; LOSS OF 1000-1250 FT ALT; UNABLE TO RECALL VSI. REGAINED CTL OF ACFT; CLBED BACK TO FL370 AND RPTED SEVERE TURB AND DEV TO CTR. CTR STATED NO PAPERWORK NECESSARY BUT BETTER SAFE THAN SORRY. SEATBELT SIGN WAS OFF BUT NO PAX UP AT THE TIME OF INCIDENT. NO INJURIES RPTED. FLT CONTINUED UNEVENTFULLY.

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.