Carbon molecular sieve (CMS) membranes show high performance for various critical gas pair separations with excellent scalable manufacturability. For practical applications it is important to evaluate such membranes for resistance to contaminants possibly present in feed streams related to an onboard inert gas generation system (OBIGGS) for aerospace applications. Here we report the performance of CMS membranes prepared by optimized dual temperature secondary oxygen doping (DTSOD) in the presence of aggressive contaminants, potentially in the bleed air of aircraft. Such feed can be used to eliminate the need for a separate compressor in membrane systems to create nitrogen enriched stream for fuel tank inerting, and we considered this case using simulated engine bypass air. Our CMS membranes were exposed to different humidity levels, combinations of gaseous contaminants (denoted as Class 'A'), and ozone to study the membrane performance for O-2/N-2 separation with time at high temperatures. The CMS shows a robust nature under such aggressive feed conditions especially at or above 160 degrees F (71 degrees C) under steady-state operation with an attractive performance under long-term exposure.