Widebody transport at high altitude cruise descended below assigned altitude due to turbulence.

Attributes
ACN	279257
Time
Date	199407
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : pit
State Reference	PA
Altitude	msl bound lower : 42000 msl bound upper : 43000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zob
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 4000 flight time type : 210
ASRS Report	279257
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather inflight encounter other non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	controller : issued new clearance flight crew : exited adverse environment
Consequence	Other
Miss Distance	vertical : 1000
Supplementary
Primary Problem	Weather
Air Traffic Incident	Pilot Deviation

Narrative:

At cruise, FL430, we hit clear air turbulence. Autoplt was on. Request by this captain for 'lower' was given a 'standby.' turbulence increased to moderated and aircraft started to roll right. Captain took control, disengaged autoplt, and requested immediate clearance for descent as he began a gradual (500 FPM) descent. Vectors were given and then finally a clearance to FL3?? (I think FL350). At this point, we were at FL420 with known traffic at FL410 off to the north (horizontal distance unknown). No further incident occurred on this flight. Difficulty developed because of limited maneuvering room with cumulus buildups in area and controller saturation at time of descent request.

Original NASA ASRS Text

Title: WDB AT HIGH ALT CRUISE DSNDED BELOW ASSIGNED ALT DUE TO TURB.

Narrative: AT CRUISE, FL430, WE HIT CLR AIR TURB. AUTOPLT WAS ON. REQUEST BY THIS CAPT FOR 'LOWER' WAS GIVEN A 'STANDBY.' TURB INCREASED TO MODERATED AND ACFT STARTED TO ROLL R. CAPT TOOK CTL, DISENGAGED AUTOPLT, AND REQUESTED IMMEDIATE CLRNC FOR DSCNT AS HE BEGAN A GRADUAL (500 FPM) DSCNT. VECTORS WERE GIVEN AND THEN FINALLY A CLRNC TO FL3?? (I THINK FL350). AT THIS POINT, WE WERE AT FL420 WITH KNOWN TFC AT FL410 OFF TO THE N (HORIZ DISTANCE UNKNOWN). NO FURTHER INCIDENT OCCURRED ON THIS FLT. DIFFICULTY DEVELOPED BECAUSE OF LIMITED MANEUVERING ROOM WITH CUMULUS BUILDUPS IN AREA AND CTLR SATURATION AT TIME OF DSCNT REQUEST.

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.