Abstract: Thermal aging of aircraft cables can markedly degrade their flame-retardant performance, thereby increasing the risk of onboard fire. In this study, accelerated thermal aging was conducted at 200 °C for 10 days to simulate the long-term service condition of PTFE-insulated cables. The effects of aging on combustion behavior were systematically investigated using cone calorimetry in combination with microstructural characterizations. The results indicate that thermal aging induces scission of C–F bonds in PTFE molecular chains, while surface cracks and pores facilitate decomposition. After aging, the ignition temperature decreased by 4.1%, the time to ignition (TTI) was shortened by 12–25%, and the peak heat release rate (pHRR) increased by 17.69% at 50 kW m⁻². Meanwhile, the peak smoke production rate at 70 kW m⁻² rose by 7.3%, and CO₂ release occurred 20 s earlier. These findings confirm that thermal aging exacerbates combustion intensity and smoke-related toxicity by deteriorating the microstructure of PTFE. This work provides experimental evidence and theoretical insights to support lifetime assessment and fire prevention strategies for aircraft cables.