As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED WHEN REDUCING POWER FOR DESCENT THE COCKPIT AIR BEGAN TO SMELL. MAINTENANCE PERFORMED VISUAL INSPECTION OF THE LEFT AIR CYCLE MACHINE AND THE ENGINE BLEED AIR CONNECTIONS. THE COCKPIT AIR DISTRIBUTION AIR FILTER WAS REPLACED AND THE AIRCRAFT WAS RETURNED TO SERVICE.