What was found
AIRCRAFT WAS GROUNDED: VERY STRONG DIRTY SOCK SMELL AFTER TAKEOFF THROUGHOUT CABIN AND FLIGHT DECK. FLIGGHT CREW DONNED OXYGEN MASKS AND ACCOMPLISHED SMOKE ODOR FUME CHECKLIST. AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO CLT WHERE IT LANDED SAFELY WITHOUT FURTHER INCIDENT. MAINTENANCE FOUND THE APU STARTER O-RING LEAKING AND REPLACED IT PER AMM 49-42-21. A SATISFACTORY LEAK CHECK WAS ACCOMPISHED AND NO ODORS WERE NOTED.