Applying the traditional equitable principle of unjust enrichment, we conclude that the judgment requiring McCutchen to provide full reimbursement to US Airways constitutes inappropriate and inequitable relief. Because the amount of the judgment exceeds the net amount of McCutchen’s third-party recovery, it leaves him with less than full payment for his emergency medical bills, thus undermining the entire purpose of the Plan. At the same time, it amounts to a windfall for US Airways, which did not exercise its subrogation rights or contribute to the cost of obtaining the third-party recovery. Equity abhors a windfall. See Prudential Ins. Co. of America v. S.S. American Lancer, 870 F.2d 867, 871 (2d Cir. 1989).