Ken Griffin's Citadel Advisors, Pacific Investment Management Co. and Western Asset Management Co. are among the investment firms poised to own equity in Spirit Airlines Inc. after the budget carrier restructures its balance sheet in bankruptcy. The three firms are part of a group that owns Spirit's 8% senior secured notes due in 2025 and is supporting the company's restructuring plan, according to a Monday court filing. Those notes, along with convertible bonds, will be exchanged for equity in Spirit once it exits bankruptcy next year, according to a description of the restructuring plan submitted in bankruptcy court.