B757 CREW HAD ALT EXCURSION IN ZDC CLASS A.

Narrative

WE WERE GIVEN CLRNC TO CROSS AT FL260; BECAUSE THE ARR CHART HAD 'EXPECT KERNO AT FL260' AND 'EXPECT SOMTO AT 13000 FT;' I HAD ALREADY PROGRAMMED THESE ALTS NEXT TO THESE FIXES ON THE LEGS PAGE. WE DSNDED TO FL260 IN VNAV AND UPON LEVELING; I PROGRAMMED FL260 INTO THE CRUISE ALT ON THE CRUISE PAGE. SUBSEQUENTLY; AT KERNO ATC GAVE US 'CROSS SOMTO AT 13000 FT; MAINTAIN 310 KTS OR BETTER.' I ALREADY HAD 13000 FT PROGRAMMED ON THE LEGS PAGE NEXT TO SOMTO AND I SET 13000 FT ON THE MCP. THEN I WENT TO THE DSCNT PAGE AND PROGRAMMED 330 KTS. AS I SWITCHED TO THE PROGRESS PAGE TO SEE HOW FAR AWAY OUR TOP OF DSCNT POINT WAS GOING TO BE; I FELT THE AUTOTHROTTLES ADD PWR TO SPD UP (WHICH I EXPECTED). THEN I HEARD THE FO SAY 'IT'S CLBING.' LOOKING BACK AT THE INSTS; I SAW 2500 FPM UP ON THE VSI; AND 26700 FT. I DISCONNECTED THE AUTOPLT AND HAND FLEW IT BACK DOWN TO FL260. THE FO DOUBLE-CHKED AND AGREED THERE WAS NO REASON IT SHOULD CLB: CRUISE ALT SET IN FMS WAS FL260. ALT IN MCP WAS 13000 FT WITH 13000 FT NEXT TO SOMTO ON THE LEGS PAGE. BOTH VNAV AND LNAV SELECTED.