14 CFR § 158.39 - Use of excess PFC revenue.
(a) If the PFC revenue remitted to the public agency, plus interest earned thereon, exceeds the allowable cost of the project, the public agency must use the excess funds for approved projects or to retire outstanding PFC-financed bonds.
(b) For bond-financed projects, any excess PFC revenue collected under debt servicing requirements shall be retained by the public agency and used for approved projects or retirement of outstanding PFC-financed bonds.
(d) Within 30 days after the authority to impose a PFC has expired or been terminated, the public agency must present a plan to the appropriate FAA Airports office to begin using accumulated PFC revenue. The plan must include a timetable for submitting any necessary application under this part. If the public agency fails to submit such a plan, or if the plan is not acceptable to the Administrator, the Administrator may reduce Federal airport grant program apportioned funds.