Verification and validation of operational software of the flight control computer, which is flight safety critical, is very important to prove correctness and faultness of the software. To verify the real-time softare requirement on operational software of flight control computer, real-time software internal parameter and variable monitoring technics on hardware-in-the-loop environment, similar to on-flight environment, is required. This paper describes flight safety critical software validation and verificiation environment using standard debugging interface, NEXUS 5001.