Narrative:

On climb out of dtw on the 202 degree radial to vwv, encountered cumulo nimbus and thunderstorms. Reported tops at FL330, starting at about FL180. On leveloff, hit severe updraft. Autoplt couldn't hold, clicked off autoplt. Aircraft climbed to FL294 for 10 seconds. Started descent immediately to FL290. Told ATC, informed them of our altitude. No further discussion (very unstable air all altitudes).

Google
 

Original NASA ASRS Text

Title: B727 ACFT AT LEVELOFF HIT SEVERE UPDRAFT RESULTING IN ALT OVERSHOT OF 400 FT BEFORE RPTR CAPT COULD RETURN ACFT TO ASSIGNED ALT.

Narrative: ON CLBOUT OF DTW ON THE 202 DEG RADIAL TO VWV, ENCOUNTERED CUMULO NIMBUS AND TSTMS. RPTED TOPS AT FL330, STARTING AT ABOUT FL180. ON LEVELOFF, HIT SEVERE UPDRAFT. AUTOPLT COULDN'T HOLD, CLICKED OFF AUTOPLT. ACFT CLBED TO FL294 FOR 10 SECONDS. STARTED DSCNT IMMEDIATELY TO FL290. TOLD ATC, INFORMED THEM OF OUR ALT. NO FURTHER DISCUSSION (VERY UNSTABLE AIR ALL ALTS).

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.