What was found
IAH - FLIGHT 2281, AFTER TAKEOFF WHEN PACKS SELECTED ON, COCKPIT AND CABIN IMMEDIATELY FILLED WITH SMOKE AND PACK 2 VALVE FAIL ADV ON EICAS. THE AIRCRAFT RETURNED TO IAH WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED THE AIRCRAFT AND REMOVED AND REPLACED THE NUMBER 1 ACM, OPERATIONALLY CHECKED WITH NO DEFECTS, AND THE AIRCRAFT WAS APPROVED FOR RETURN TO SERVICE.