What was found
AIRCRAFT LOST AUTO PRESSURIZATION AT FL240 AND CRUISE POWER. CREW ATTEMPTED MANUAL CONTROL BUT WAS UNABLE TO KEEP THE CABIN FROM CLIMBING. COMPLIED WITH COM PROCEDURES. FLIGHT ACCOMPLISHED AN EMERGENCY DESCENT TO 10,000 FEET. MASK DID NOT DEPLOY AND AIRCRAFT CONTINUED TO AN UNEVENTFUL LANDING AT MSY. MAINTENANCE FOUND THE ACM EXHAUST DUCT SEPARATED. DUCT WAS REINSTALLED. OPERATIONAL CHECK OK. AIRCRAFT RETURNED TO SERVICE.