What was found
CABIN ALTIUDE CAME ON @ 28000' EARS POPPED, CABIN ALTITUDE FLUCTUATED UP, EMERGENCY DECENT, CABIN ALTITUDE MODERATED IN AND OUT OF CONTROL, COCKPIT GOT WARM. AIRCRAFT LANDED IN LAL WITH OUT FURTHER INCIDENT. AIRCRAFT GROUNDED BY MAINTENANCE. MAINTENANCE DETERMINED FWD EQUIPMENT COOLING SUPPLY CHECK VALVE FOUND UNSECURED. RE-SECURED CHECK VALVE IAW B767 AMM 21-58-02 OPS AND LEAK CHECK SATISFACTORY. VISUALLY INSPECTED LH AND RH COOLING PACKS AND ASSOCIATED DUCTING NO DISCREPANCIES NOTED AT THIS TIME PERFORMED EXCESSIVE CABIN PRESSURE LEAKAGE CHECKED TWICE IAW B767 AMM 05-51-24 TEMP AND PRESSURE CORRECT, TEST RESULTS SATISFACTORY. BOTH PACKS OPERATING NORMALLY. AIRCRAFT RETURNED TO SERVICE