Narrative:

Flight was being vectored for a visual approach to runway 21 at dca. WX was VMC, surface winds reported calm. We were flying in smooth air. There was a line of thunderstorms to the north and west, but no echo closer than 10 mi to our position. Without warning, the aircraft entered an uncommanded descent, and began pitching violently about all axes. I disengaged the autoplt and endeavored to hold wings level. I was unable to arrest the descent. I then told the first officer to report that we were encountering severed turbulence, and were turning directly toward dca. Approach controller cleared the flight for a visual approach to runway 21 (dca traffic was landing to the south). Turbulence subsided about 5 mi from dca, and ceased at about 2 mi. We landed in calm winds. When we arrived at our gate, some 4 mins later, winds were from the northwest, gusting to 30 mph.

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Original NASA ASRS Text

Title: DURING VECTORS FOR A VISUAL APCH, THE CAPT OF AN MDT LOST CTL MOMENTARILY DUE TO TURB RESULTING IN DSCNT FROM ASSIGNED ALT.

Narrative: FLT WAS BEING VECTORED FOR A VISUAL APCH TO RWY 21 AT DCA. WX WAS VMC, SURFACE WINDS RPTED CALM. WE WERE FLYING IN SMOOTH AIR. THERE WAS A LINE OF TSTMS TO THE N AND W, BUT NO ECHO CLOSER THAN 10 MI TO OUR POS. WITHOUT WARNING, THE ACFT ENTERED AN UNCOMMANDED DSCNT, AND BEGAN PITCHING VIOLENTLY ABOUT ALL AXES. I DISENGAGED THE AUTOPLT AND ENDEAVORED TO HOLD WINGS LEVEL. I WAS UNABLE TO ARREST THE DSCNT. I THEN TOLD THE FO TO RPT THAT WE WERE ENCOUNTERING SEVERED TURB, AND WERE TURNING DIRECTLY TOWARD DCA. APCH CTLR CLRED THE FLT FOR A VISUAL APCH TO RWY 21 (DCA TFC WAS LNDG TO THE S). TURB SUBSIDED ABOUT 5 MI FROM DCA, AND CEASED AT ABOUT 2 MI. WE LANDED IN CALM WINDS. WHEN WE ARRIVED AT OUR GATE, SOME 4 MINS LATER, WINDS WERE FROM THE NW, GUSTING TO 30 MPH.

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.