MLT X NON ADHERENCE TO ATC CLRNC UNAUTHORIZED CLB FROM ASSIGNED ALT HAD LTSS FROM Y.

Narrative

MLT X DURING CLBOUT FROM TYNDALL AFB; FL; AND AFTER PASSING FL180 WE REQUESTED FL220 FOR A FINAL ALT AND THE CTLR TOLD US TO STANDBY ON FL220. THE L SEAT PLT WAS FLYING THE ACFT ON AUTOPLT AND I WAS IN THE R SEAT WORKING THE RADIOS AND PROGRAMMING THE SCNS WHICH IS OUR NAV SYS WITH A KEYPAD AND CRT. AT SOME POINT DURING THE CLBOUT; WHILE PROGRAMMING THE SCNS AND MAKING A CALL TO CONFIRM A FREQ CHANGE; I THOUGHT WE HAD BEEN CLRED TO FL220. AFTER THE L SEAT PLT LEVELED THE AIRPLANE AT FL200; I TOLD HIM 'I THINK HE CLRED US TO 220.' THE FLT ENGINEER HAD JUST COME BACK ON HEADSET AND HEARD ME SAY '...CLRED TO 220.' AS WE PASSED THROUGH FL205 ATC CALLED AND ASKED ABOUT OUR ALT. WE SAID WE WERE PASSING 205 FOR 220 AND ATC SAID NEGATIVE TURN R IMMEDIATELY AND DSND TO 200; TFC 12 O'CLOCK AND 5 MI; FL210. WE SAW THE TWIN ENG COMMUTER ACFT PASS ABOVE US AND OFF TO OUR L. I THINK MY PREOCCUPATION WITH THE SCNS SYS AND THE FACT THAT OUR AIRPLANE HAS NO SORT OF AN ALT REMINDER WERE 2 CONTRIBUTING FACTORS TO THIS INCIDENT. SUPPLEMENTAL INFO FROM ACN 201213: WE WERE CLRED TO FL200 AND REQUESTED FL220. AFTER I LEVELED AT FL200 THE COPLT STATED WE HAD BEEN CLRED TO FL220. I ASSUMED I HAD MISSED THAT CLRNC AND STARTED A CLB TO FL220. PASSING THROUGH 205 THE CTLR ASKED US OUR ALT AND WHEN WE TOLD HIM; HE TOLD US WE WERE ONLY CLRED TO FL200 TO TURN R.