B737-200 flight crew loses 400 ft in altitude during an encounter with turbulence at 10000 ft.

Attributes
ACN	395900
Time
Date	199803
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : pit
State Reference	PA
Altitude	msl bound lower : 9600 msl bound upper : 10000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : pit
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Route In Use	arrival other enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 180 flight time total : 9000 flight time type : 1600
ASRS Report	395900
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather inflight encounter other non adherence : clearance other anomaly
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance flight crew : regained aircraft control flight crew : exited adverse environment
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	Pilot Deviation other

Narrative:

Copilot was flying into pittsburgh from roa. Leveled off 10000 ft 30 mi south of pittsburgh in tops of overcast. Ride was moderate turbulence at this time. Aircraft entered downdraft and descended 300-400 ft before descent could be arrested. Aircraft was then climbed back to 10000 ft. ATC made no mention of our deviation other than if we got the descent clearance to 4000 ft. We acknowledged that we had not but then took clearance and descended down below clouds. Subsequently we were vectored for approach and landing. Do not believe that there is anything we could have done to prevent this occurrence. WX played a factor as flight through clouds presented moderate to severe turbulence most of the time. Condition persisted around airport and continued for many hours. Downdrafts and updrafts tend to be hard to predict and this is first time I have encountered this type of situation.

Original NASA ASRS Text

Title: B737-200 FLC LOSES 400 FT IN ALT DURING AN ENCOUNTER WITH TURB AT 10000 FT.

Narrative: COPLT WAS FLYING INTO PITTSBURGH FROM ROA. LEVELED OFF 10000 FT 30 MI S OF PITTSBURGH IN TOPS OF OVCST. RIDE WAS MODERATE TURB AT THIS TIME. ACFT ENTERED DOWNDRAFT AND DSNDED 300-400 FT BEFORE DSCNT COULD BE ARRESTED. ACFT WAS THEN CLBED BACK TO 10000 FT. ATC MADE NO MENTION OF OUR DEV OTHER THAN IF WE GOT THE DSCNT CLRNC TO 4000 FT. WE ACKNOWLEDGED THAT WE HAD NOT BUT THEN TOOK CLRNC AND DSNDED DOWN BELOW CLOUDS. SUBSEQUENTLY WE WERE VECTORED FOR APCH AND LNDG. DO NOT BELIEVE THAT THERE IS ANYTHING WE COULD HAVE DONE TO PREVENT THIS OCCURRENCE. WX PLAYED A FACTOR AS FLT THROUGH CLOUDS PRESENTED MODERATE TO SEVERE TURB MOST OF THE TIME. CONDITION PERSISTED AROUND ARPT AND CONTINUED FOR MANY HRS. DOWNDRAFTS AND UPDRAFTS TEND TO BE HARD TO PREDICT AND THIS IS FIRST TIME I HAVE ENCOUNTERED THIS TYPE OF SIT.

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.