Air carrier had altitude deviation while diverting around trw.

Attributes
ACN	180941
Time
Date	199106
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : obh
State Reference	NE
Altitude	msl bound lower : 37000 msl bound upper : 39000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zmp tracon : bdl
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : commercial pilot : cfi pilot : atp pilot : instrument
Experience	flight time last 90 days : 150 flight time total : 9500 flight time type : 250
ASRS Report	180941
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather other anomaly
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	other

Narrative:

Deviating around trw (approximately 40 mi) south and roughly paralleling wind, while in cloud with lt-mdt turbulence, encountered extremely strong updraft that forced automatic-disconnect of autoplt and approximately 2000' altitude excursion prior to manually stabilizing aircraft. No traffic conflict occurred and no injuries or damage sustained, but significant clearance deviation occurred. Captain (reporter) broadcast 'pan' message on center frequency and ATC immediately reclred 'block 370-410.' flight returned to FL370 within approximately 2 mins after event. Turbulence never greater than 'mod' even though updraft of approximately 5000 FPM experienced. After situation assessment and contact with both ATC and company, flight proceeded with normal operations to destination. All standard trw avoidance procedure had been utilized (1 KT sep for every KT of wind at altitude), seat belt sign was on prior to event, and aircraft was cleared to deviation and was doing so while captain was discussing alternate routings with company dispatch when event occurred. No specific recommendations to be made as crew reacted/coordination well as did ATC. Situational awareness was high which perhaps contributed to normalizing the situation in a timely manner, but was unable to prevent it.

Original NASA ASRS Text

Title: ACR HAD ALT DEVIATION WHILE DIVERTING AROUND TRW.

Narrative: DEVIATING AROUND TRW (APPROX 40 MI) S AND ROUGHLY PARALLELING WIND, WHILE IN CLOUD WITH LT-MDT TURB, ENCOUNTERED EXTREMELY STRONG UPDRAFT THAT FORCED AUTO-DISCONNECT OF AUTOPLT AND APPROX 2000' ALT EXCURSION PRIOR TO MANUALLY STABILIZING ACFT. NO TFC CONFLICT OCCURRED AND NO INJURIES OR DAMAGE SUSTAINED, BUT SIGNIFICANT CLRNC DEV OCCURRED. CAPT (RPTR) BROADCAST 'PAN' MESSAGE ON CTR FREQ AND ATC IMMEDIATELY RECLRED 'BLOCK 370-410.' FLT RETURNED TO FL370 WITHIN APPROX 2 MINS AFTER EVENT. TURB NEVER GREATER THAN 'MOD' EVEN THOUGH UPDRAFT OF APPROX 5000 FPM EXPERIENCED. AFTER SITUATION ASSESSMENT AND CONTACT WITH BOTH ATC AND COMPANY, FLT PROCEEDED WITH NORMAL OPS TO DEST. ALL STANDARD TRW AVOIDANCE PROC HAD BEEN UTILIZED (1 KT SEP FOR EVERY KT OF WIND AT ALT), SEAT BELT SIGN WAS ON PRIOR TO EVENT, AND ACFT WAS CLRED TO DEV AND WAS DOING SO WHILE CAPT WAS DISCUSSING ALTERNATE ROUTINGS WITH COMPANY DISPATCH WHEN EVENT OCCURRED. NO SPECIFIC RECOMMENDATIONS TO BE MADE AS CREW REACTED/COORD WELL AS DID ATC. SITUATIONAL AWARENESS WAS HIGH WHICH PERHAPS CONTRIBUTED TO NORMALIZING THE SITUATION IN A TIMELY MANNER, BUT WAS UNABLE TO PREVENT IT.

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.