Flight compatibility certification is performed to substantiate the compatibility between ALQ-X ECM pod and KF-16D/RF-4C aircraft. A certification plan for the ALQ-X flight compatibility is established. Similarity analysis, mass/inertia analysis, structural analysis/test, and ground vibration test/flutter analysis are made to support the safety of MIL-HDBK-1763 Test 250 (Captive compatibility flight profile). Aircraft flew along flight envelope boundary with representative ALQ-X configurations. Handling qualities are evaluated by comparing flight characteristics of the aircraft with and without ALQ-X. Structural integrity and endurance is evaluated using measured flight test data. Results of these flight tests showed that ALQ-X is compatible with KF-16D/RF-4C without altering the flight envelope which has originally been certified for ALQ-88 and ALQ-119 ECM pods. ALQ-X certification program made following technical achievements: Type III certification for foreign designed fighter, flutter analysis program development using GVT results, and utilization of MIL-STD-1553B data bus in flight test.