(1) In the cases prescribed in paragraphs (a) through (d) of §157.3, 90 days in advance of the day that work is to begin; or
(2) In the cases prescribed in paragraphs (e) through (g) of §157.3, 90 days in advance of the planned implementation date.
(b) Notwithstanding paragraph (a) of this section—
(1) In an emergency involving essential public service, public health, or public safety or when the delay arising from the 90-day advance notice requirement would result in an unreasonable hardship, a proponent may provide notice to the appropriate FAA Airport District/Field Office or Regional Office by telephone or other expeditious means as soon as practicable in lieu of submitting FAA Form 7480–1. However, the proponent shall provide full notice, through the submission of FAA Form 7480–1, when otherwise requested or required by the FAA.
(2) notice concerning the deactivation, discontinued use, or abandonment of an airport, an airport landing or takeoff area, or associated taxiway may be submitted by letter. Prior notice is not required; except that a 30-day prior notice is required when an established instrument approach procedure is involved or when the affected property is subject to any agreement with the United States requiring that it be maintained and operated as a public-use airport.