During scheduled winter airtanker inspections as part of the USFS' Integrated Operational Field Evaluation (I-OFE), it was discovered that certain airtankers that had flown Fortress North America's (Fortress') proprietary, magnesium chloride-based aerial fire retardants revealed significant signs of corrosion in areas where build-up of the retardant had occurred. The findings from this more extensive inspection raised aircraft safety concerns, prompting the USFS' decision to inform Compass Minerals on March 22, 2024, that it would be "unable to define the scope and associated terms and conditions of a new contract" with the company until the National Transportation Safety Board (NTSB) and National Institute of Standards and Technology (NIST) conducted a coordinated, independent assessment of the findings.