“Sep 19, 2001: Late on this day, the agency [Federal Aviation Administration] permitted limited resumption of general aviation Part 91 operations under Visual Flight Rules (VFR). Exceptions included flight in Enhanced Class B (ECB) airspace, meaning that VFR flying was not allowed over, through, or ‘under the shelf’ of the Class B airspace category surrounding major airports. (Later, ECB was defined to exclude airspace above 18,000 feet.) Other types of Part 91 VFR operations not permitted to resume were: civil flight training; banner towing; circling or loitering by news reporting helicopters; traffic watch; sightseeing; and airship/blimp flights.”
– FAA, “Chronology of the September 11 Attacks and Subsequent Events Through October 24, 2001,” FAA Believed Second 9/11 Plane Heading Towards NY for Emergency Landing, The National Security Archive, Sep. 9, 2005