PLT OF MTR OVERSHOT DSCNT ALT HAD TFC CONFLICT. VIOLATED BY ARTCC.

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ON A MIL TRAINING MISSION WITH ASSIGNED UNIT NAS PENSACOLA; FL. I WAS OPERATING A MTR IN THE CAPACITY OF INSTRUCTOR PLT WITH A STUDENT NFO IN THE BACKSEAT. WE WERE ON OUR FIRST LEG TO MAXWELL AFB ON AN OUT/IN. CLRNC WAS TO THE HOLDING FIX LOMAX. CLRED TO DSND FROM FL260 TO FL240. SHORTLY AFTER 3 NEW ALT CLRNC 220; 200; 190 AND ONE FREQ SWITCH FROM 290.5 TO 297.4. STUDENT WAS BEHIND AND BECAME A CONTRIBUTING FACTOR. WOULD STEP ON CTLRS UHF COM. STUDENT'S ICS WOULD BLOCK INSTRUCTORS UHF. ATTEMPTING TO KEEP COPIOUS NOTES I GOT DISTR AND DSNDED THROUGH MY ASSIGNED ALT OF FL190. I REMEMBER SEEING 18700 ON MY ALTIMETER. IMMEDIATELY CORRECTED BACK TO FL190. CTLR ASKED ALT. RESPONDED 300 FT LOW AND IMMEDIATELY CORRECTED BACK. AT THAT TIME HE GAVE PHONE TO CONTACT ON DECK FOR POSSIBLE ALT DEV. I FOUND THIS PROC VERY NERVE RACKING. I STILL HAD TO EXECUTE AN ACTUAL APCH WITH THE THOUGHT OF CAREER ENDING FLT VIOLATION IN THE BACK OF MY MIND! ONCE ON DECK SPOKE TO FSDO OFFICE. THEY INFORMED ME MY MODE C TRIGGERED A SNITCH PATCH; SHOWING 18100. A MIL 1.8 NM AT FL180 ASSIGNED; REASON FOR COMPUTER ALARM. DISTRS FROM MY STUDENT BROKE DOWN MY SCAN LED TO MY INACTION OF NOT LEVELING AT FL190. ALTHOUGH I DON'T RECALL BEING ANY LOWER THAN 18700 FT. I WOULD RECOMMEND CHANGING THE PROC FOR CONTACTING UNTIL ONCE SAFELY ON DECK! IT WAS VERY NERVE RACKING.