The correct answer is B) Filing a formal grievance with a company and union agreed-upon arbitrator for binding arbitration. This is typically the last step in the grievance resolution process established by the collective bargaining agreement between the company and the crew member's union. After attempting to resolve the issue through the lower-level channels, such as the crew member and supervisor or the onboard union representative, the final step is to submit the grievance to an independent arbitrator agreed upon by both the company and the union. This arbitrator's decision is binding, meaning it must be accepted by both parties, and represents the final resolution of the grievance. The other options, while potentially part of the overall grievance process, do not represent the final, binding step as outlined in the question.