As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED DUE TO: WHILE DESCENDING FROM FL210 AND PASSING THROUGH FL200, CABIN ALTITUDE WARNING CAME ON. AIRCRAFT EMERGENCY LANDED SAFELY AT DFW. REMOVED AND REPLACED FLEXIBLE DUCT FORWARD OF THE ACM LEFT HAND SIDE. PER AMM 21-51-04. NO LEAKS NOTED.