CAPT OF A B727 OVERSHOT CRUISE LEVELOFF ALT DUE TO DISTR OF SOCIALIZING WITH THE OTHER CREW MEMBERS.

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WE HAD BEEN CLRED TO OUR FILED CRUISING ALT OF FL330. CLBING THROUGH APPROX FL270; ATC TOLD US TO STOP AT FL290. ALT WAS READ BACK; PUT IN 'WINDOW' AND CONFIRMED BY THE CAPT (PF). AT FL280 STANDARD CALLOUT OF '1 TO GO' WAS MADE BY COPLT AND REPEATED BY CAPT. AT APPROX FL285 CAPT HANDED COPLT PICTURE OF AIRPLANE HE OWNED. COPLT BEGAN LOOKING DOWN AT PICTURE AS WELL AS THE SO WHO WAS LOOKING OVER HIS SHOULDER. AT FL292 COPLT AND SO WERE ALERTED SIMULTANEOUSLY BY CAPT PULLING THROTTLES BACK AND PUSHING NOSE OVER. BEGAN DSCNT BACK TO FL290 AFTER CLBING TO FL294. ATC NEVER SAID ANYTHING ABOUT DEV. CONTRIBUTING FACTORS TO ALTDEV: CAPT ADMITTED TO BEING DISTRACTED BY DISCUSSION OF HIS AIRPLANE AND FORGOT TO LEVEL AT FL290. THE AUTOPLT IN B727 HAS NO ALT CAPTURE MODE. PF MUST ARREST ASCENT/DSCNT; THEN ENGAGE ALT HOLD. ALT ALERTER (AWI) DOES NOT 'CHIME' AS AN ALERT THAT YOU ARE REACHING DESIRED ALT. ONLY 'CHIMES' AFTER DEV OF APPROX +/-1000 FT. COMPANY SOP (STANDARD OPERATING PROCS) HAVE PLTS CONFIRM 2000 FT AND 1000 FT TO LEVELOFF ALTS; BUT THERE IS NO CALL AT LEVELOFF. THE CAUSE OF THIS DEV IS OBVIOUS. ALL 3 PLTS BEING DISTRACTED SIMULTANEOUSLY. HOWEVER; AN ALT CAPTURE MODE ON THE AUTOPLT; A 200 FT TO LEVELOFF CHIME OR A MANDATORY LEVELOFF CALL; WOULD HAVE AVERTED THIS DEV.