 He was cleared by the New Orleans Air Route Traffic Control Center (ARTCC - ZNO) located in the terminal building at New Orleans Lakefront Airport to descend to and maintain 5,000 feet and to report leaving 8,000 feet.This air traffic control instruction/clearance was issued through National Airlines' radio station/office at Pensacola, Florida, a normal procedure before making the approach to Moisant International Airport (KMSY) in New Orleans.At that time the control tower at Moisant reported a ceiling of 1,200 feet with three-fourths of a mile visibility, light fog and rain.