As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EXPERIENCED A BURNING SMELL IN THE COCKPIT WITH A SMOKY HAZE BUILDING IN THE COCKPIT, DISSIPATED AS WE DESCENDED. PERFORMED TROUBLESHOOTING PER FIM 21-20-00. FOUND NR 1 PACK ACM TO HAVE FAILED. REMOVED AND REPLACED NR 1 PACK ACM PER AMM 21-51-03. OPC GOOD. NO SMOKE SMELL