What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO PHX DUE TO THE FLIGHT CREW REPORTING A DIRT SOCK SMELL RIGHT AFTER ROTATION ON TAKEOFF. THE AIRCRAFT LANDED SAFELY AT PHX AND TAXIED TO THE GATE UNDER ITS OWN POWER. FOUND NO SIGNS OF LEAKS OR CONTAMINATION IN APU COMPARTMENT. NOTED DURING THE INSPECTION OF THE PACK BAYS THAT BOTH LT & RT PACK PLENUMS WERE DELAMINATED AND LT PACK PLENUM WAS COLLAPSED. NO EVIDENCE OF OIL OR FOREIGN FLUID CONTAMINATION PRESENT IN THE PACK BAYS. REPLACED BOTH PACK PLENUMS IAW AMM 21-52-22 AND ACCOMPLISHED A SATISFACTORY LEAK / OPERATIONAL CHECK WITH NO ODORS OR ISSUES NOTED.