2 EVENTS ON A B747-200 CARGO FLT; SMOKE IN THE COCKPIT AND AN ALTDEV EXCURSION OF 400 FT BELOW ASSIGNED ALT DURING APCH INTO ANC; AK.

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SHORTLY AFTER DSNDING THROUGH 10000 FT MSL; THE FE RPTED SMOKE IN THE CABIN. BLUISH-COLORED SMOKE WAS INDEED EVIDENT AND WE COULD SMELL AN OILY-SMOKE SCENT. THE FE WENT BRIEFLY DOWNSTAIRS TO MAKE CERTAIN THAT THERE WAS NOT A FIRE IN THE MAIN CARGO AREA. WHEN THE FE RETURNED; THE FO AND I WERE ALREADY USING OXYGEN MASKS. I TOLD THE APCH CTLR THAT WE HAD EVIDENCE OF SMOKE IN THE COCKPIT/CABIN AND THAT I WANTED THE EMER EQUIP STANDING BY. WE RECEIVED SOME DELAYING VECTORS AS WE WERE DSNDING TO THE ASSIGNED 4000 FT MSL; AND THERE WAS CONSIDERABLE AMOUNTS OF CONVERSATION; BOTH ON THE INTERPHONE WITHIN THE COCKPIT; AS WELL AS WITH ATC. JUMPING FROM ONE AUDIO SOURCE TO ANOTHER (INTERPHONE BUTTON ON THE AUDIO SELECTOR PANEL; THEN PUSHING THE COM #1 BUTTON FOR ATC) WAS A SIGNIFICANT FACTOR; DUE TO RUNNING EMER; APCH AND LNDG CHKLISTS; AS WELL AS NORMAL COMMANDS AND RESPONSES (FLAP SELECTIONS; LNDG GEAR; ETC). WE LEVELED OFF AT 4000 FT BRIEFLY; BUT THE PF WAS HAND-FLYING AND INADVERTENTLY DSNDED TO 3600 FT MSL DURING A HIGH WORKLOAD TIME. ON SEVERAL OCCASIONS; I COMMUNICATED ON THE 'WRONG AUDIO BUTTON;' AND MAY HAVE USED LANGUAGE ON ONE OCCASION THAT WAS INAPPROPRIATE FOR STANDARD ATC COMS. THE ALT DISCREPANCY WAS QUICKLY CORRECTED. I BELIEVE WE ALSO MISSED A HEADING ASSIGNMENT SOMETIME DURING THIS HIGH WORKLOAD TIME-FRAME. THE DIFFICULTY OF COMMUNICATING WITH OXYGEN MASKS ON; USING AT LEAST 2 SOURCES OF AUDIO; WHILE PERFORMING NORMAL; ABNORMAL AND EMER CHKLISTS AND UNDER A HIGHLY STRESSFUL SCENARIO OF SMOKE AND POSSIBILITY OF FIRE WHILE AIRBORNE CANNOT BE OVEREMPHASIZED. SUPPLEMENTAL INFO FROM ACN 556791: OXYGEN MASKS WERE USED AND COM BTWN CREW MEMBERS BECAME MORE DIFFICULT. FO DSNDED 400 FT BELOW THE CLRED ALT OF 4000 FT. SHE MADE AN IMMEDIATE CORRECTION BACK TO 4000 FT. CREW CORD SUFFERED DUE TO MORE DIFFICULT COMS.