What was found
AIR TURN BACK DUE TO A PACK COOL AIR FAIL MESSAGE DURING CLIMB OUT OF KDEN AT 30,000 FT FOLLOWED BY A PACK FAIL CAS AT 40,000 FT. CREW RAN THE PACK FAIL CHECKLIST AND SWITCHED TO TRIM AIR ONLY, AFTER WHICH THE COCKPIT FILLED WITH SMOKE AND THE CREW DONNED OXYGEN MASKS AND ADVISED ATC, WHO DECLARED AN EMERGENCY ON THEIR BEHALF. AIRCRAFT LANDED WITHOUT INCIDENT AT KDEN. REPLACED AIR REGULATING VALVE IAW AMM 21-53-21 AND REPLACED AIR CYCLE MACHINE IAW MM 21-52-13. OPS AND LEAK CHECKS GOOD WITH NO CAS MESSAGE ILLUMINATED.