Time-Triggered Ethernet (TTEthernet) is increasingly being deployed in avionics, space applications and other safety-critical systems. The main reasons are its real-time determinism, support for mixed-criticality and certification. Due to the application in these safety-critical systems, TTEthernet was equipped with various fault-tolerance capabilities such as anti-masquerading and a guardian functionality. Consequently a challenge for this kind of system is the realistic and effective validation that can evaluate multiple implementations from different vendors including the protocol itself using Fault Injection (FI). This paper presents an FI framework for TTEthernet using an FPGA which is connected to the network under test and injects faults according to a cut-through paradigm. The proposed solution improves previous FI systems, since it addresses time-aware networks and has the capability to target individual traffic classes such as Rate Constrained (RC) and Time Triggered (TT) frames. This provides better controllability, including the ability of the framework to target TTEthernet synchronisation mechanism.