Airframe structures, especially composite structures, are prone to damage by tool drops, bird strikes, hailstones, etc. The authors have developed an optical fiber based impact damage detection system for composite airframe structure since 1998. In this method, impact locations are measured with the signals of multiple Fiber Bragg Grating (FBG) sensors. In case of aircraft implementation, impact information should be detected under the actual vibration condition, and both detection capability for impact localization and damage level should be improved. This paper presents the detectability assessment result from the impact tests under a simulated vibration condition. In addition, study of optimal FBG sensor direction for localization and review of damage level detection method are conducted to enhance the accuracy of detection.