Prior to the initiation of formal action to terminate eligibility for airport grant funds or authority to impose or collect passenger facility charges under this subpart, the FAA shall undertake informal resolution with the airport operator to assure compliance with the Airport Noise and Capacity Act of 1990 or this part upon receipt of a complaint or other evidence that an airport operator has taken action to impose a noise or access restriction that appears to be in violation. This shall not preclude a FAA application for expedited judicial action for other than termination of airport grants and passenger facility charges to protect the national aviation system and violated federal interests. If informal resolution is not successful, the FAA will notify the airport operator in writing of the apparent violation. The airport operator shall respond to the notice in writing not later than 20 days after receipt of the notice, and also state whether the airport operator will agree to defer implementation or enforcement of its noise or access restriction until completion of the process under this subpart to determine compliance.