(a) Each public agency shall keep any unliquidated PFC revenue remitted to it by collecting carriers on deposit in an interest bearing account or in other interest bearing instruments used by the public agency's airport capital fund. Interest earned on such PFC revenue shall be used, in addition to the principal, to pay the allowable costs of PFC-funded projects. PFC revenue may only be commingled with other public agency airport capital funds in deposits or interest bearing instruments.

(b) Each public agency shall establish and maintain for each approved application a separate accounting record. The accounting record shall identify the PFC revenue received from the collecting carriers, interest earned on such revenue, the amounts used on each project, and the amount reserved for currently approved projects.

(c) At least annually during the period the PFC is collected, held or used, each public agency shall provide for an audit of its PFC account. The audit shall be performed by an accredited independent public accountant and may be of limited scope. The accountant shall express an opinion of the fairness and reasonableness of the public agency's procedures for receiving, holding, and using PFC revenue. The accountant shall also express an opinion on whether the quarterly report required under §158.63 fairly represents the net transactions within the PFC account. The audit may be --

(1) Performed specifically for the PFC account; or

(2) Conducted as part of an audit under the Single Agency Audit Act of 1983 (31 U.S.C. 7501-7) provided that the PFC is specifically addressed by the auditor.