ALT XING RESTR NOT MET DUE TO MISUNDERSTOOD COM.

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IT WAS THE FO'S LEG TO BE THE PF. HE IS A VERY SENIOR FO WITH THE COMPANY AND IS BEING UPGRADED TO CAPT. I WAS THE PNF. AS THE PNF MY DUTIES INCLUDE COMMUNICATING WITH ATC AND THE PAX. APPROX 25 MI NE OF MKK VOR; I TOLD THE PF THAT HE HAD THE #1 RADIO (ATC) WHILE I MADE MY PA. HE ACKNOWLEDGED. DURING MY PA; THE PF RECEIVED A DSCNT CLRNC. WHEN I WAS FINISHED WITH THE PA HE INFORMED ME THAT WE HAD BEEN CLRED TO DSND AT PLT'S DISCRETION TO 5000 FT; BUT TO CROSS 6 NM NE OF MKK VOR AT 6000 FT. I HAD NO REASON TO DOUBT THIS. WE BEGAN OUR DSCNT AND CROSSED THE 6 NM POINT AT 6000 FT. AT THIS TIME THE CTLR INFORMED ME THAT WE HAD BEEN CLRED TO CROSS 8 NM NE OF MKK VOR AT OR BELOW 6000 FT. NEWS TO ME. PRIOR TO LNDG; THE FO STATED HE HAD NOT GOTTEN MUCH SLEEP THE NIGHT PRIOR DUE TO A LATE DEP AT THE ARPT AND AN EVEN LATER PHONE CALL. LESSON LEARNED: DO NOT TRUST ANYONE; NO MATTER HOW SENIOR THEY AREA. EVEN IF I AM MAKING A PA OR TALKING TO DISPATCH ON THE OTHER RADIO; I WILL ALWAYS MAINTAIN A 'LISTENING WATCH' ON ATC. I WILL ALSO BEGIN ASKING MY CREW DURING THE CAPT BRIEF HOW WELL RESTED THEY ARE AND IF THEY ARE MENTALLY PREPARED FOR THE FLT.