What was found
AFTER TAKEOFF, "DUCT LEAK" AURAL AND "DUCT LEAKAGE" ON LEFT ENGINE ILLUMINATED. PERFORMED PRECAUTIONARY SHUTDOWN OF LT ENGINE. CHECKED ALL POSSIBLE SOURCES FOR WARNING. SUSPECT LT DEICE NOT REGULATING PRESSURE CORRECTLY, REPLACED VALVE. RAN LEFT ENGINE AT VARIOUS POWER SETTINGS AND BLEED CONFIGURATIONS AND DEICE BOOTS FOR REGULATING VALVE; ALL CKS GOOD. PN 38E96-6A, SN ON RR-1894, SN OFF 99-047.