The need to eliminate greenhouse gas emissions in the aviation sector makes the development of high-performance electric motors of utmost importance. The general aviation requirement of low weight and volume leads to a high electric power density. Consequently, high-performance polymers need to be used as insulation materials to endure high thermal, electrical, environmental and mechanical stresses. However, the experience with those materials under aviation stresses is limited. As failure of the electrical insulation within the electric aviation motors must be avoided at all circumstances, the failure mechanisms must be understood thoroughly. The trend to higher operation voltages in the low-pressure environment at cruising altitude makes suppressing partial discharges (PD) difficult. Meanwhile, PDs have a destructive impact on polymeric insulation materials. Therefore, the aim of this contribution is to investigate the lifetime of PEEK and PTFE samples under permanent surface discharge stress at pressures down to 200 mbar. The findings reveal a significantly disparate performance of both materials that indicates differences in the aging mechanism. The general impact of low air pressures as well as the material specificities of PEEK and PTFE should be respected when designing the insulation system for high-performance electric motors for aviation.