Laboratory and outdoor exposure testing can be used to provide controlled or well-characterized environments for understanding how environmental factors alter coating system properties that can be used to understand systems employed on aircraft. Accurate determination of the state of the coating system would help eliminate unnecessary paint removal operations and thereby reduce worker exposure to, and costs associated with, hazardous materials handling arising from paint removal and repainting operations. A commercial aircraft coating system was exposed to laboratory environmental stressors and outdoor exposure on an atmospheric exposure rack to mimic in-service environments. Equivalent circuit parameter values of electrochemical impedance spectroscopy (EIS) data were linked to mechanisms affecting the deterioration of the coating system in response to in-service environmental exposures. Laboratory and outdoor fatigue testing of the coating system and primer coating resulted in cracking of the coating layers. These cracks allowed faster ingress of electrolyte, as seen in EIS measurements, which would shorten the lifespan of the coatings. Area scans using a scanning Kelvin probe instrument were consistent with the EIS interpretation of fatigue degrading the coating barrier properties, while scanning electron microscopy (SEM) images showed an increased linear density of pretreatment cracks in the fatigued coating samples.