ALTDEV ALT OVERSHOT ON DSCNT BY ACR MLG.

Narrative

DUE TO MISCOM ON THE PART OF MYSELF AND THE CTLR; WE WERE INVOLVED IN A DSCNT TO AN ALT TO WHICH WE WERE NOT CLRED. WHILE PROCEEDING TOWARD FLAT ROCK (FAK) VOR AT FL270; WE RECEIVED A CLRNC TO CROSS FAK AT 10000 FT. THE FO CONFIRMED THAT 10000 FT WAS OUR CLRED ALT. THE CLRNC WAS RECEIVED ON A FREQ OF 127.75. I READ BACK THE CLRED ALT TO THE CTLR. WE WERE HANDED OFF TO THE NEXT CTLR ON 132.77. WHEN I CHKED IN I STATED THAT WE WERE DSNDING THROUGH FL200 TO AN ASSIGNED ALT OF 10000 FT. THE CTLR ASKED ME TO REPEAT OUR CLRED ALT. WHEN I REPEATED '10000 FT'; THE CTLR STATED THAT OUR CLRED ALT WAS FL200. THE LOWEST ALT REACHED WAS FL190; WE CLBED BACK UP TO FL200. NO APPARENT LOSS OF SEPARATION TOOK PLACE. FACTORS AFFECTING THE QUALITY OF HUMAN PERFORMANCE: THE FO WAS NEW TO THE AIRPLANE AND TO OUR COMPANY. I WAS HELPING HIM WITH PROGRAMMING THE FMC SYS. I SHOULD HAVE BEEN SUSPICIOUS OF A CLRNC TO SUCH A LOW ALT CONSIDERING THE DISTANCE FROM THE DEST. I ALSO SHOULD HAVE QUESTIONED A CLRNC TO AN 'MSL' ALT WITHOUT AN ALTIMETER SETTING BEING GIVEN. THE CTLR MAY HAVE MISSTATED THE ALT. IF HE STATED THE ALT CORRECTLY; HE SHOULD HAVE HEARD MY INCORRECT READBACK.