Unless otherwise authorized or required by ATC, no person  may operate an aircraft to, from, through, or on an airport  having an operational control tower unless two-way radio  communications are maintained between that aircraft and the  control tower. Communications must be established within  four nautical miles from the airport, up to and including 2,500  feet AGL. However, if the aircraft radio fails in flight, the PIC  may operate that aircraft and land if weather conditions are at  or above basic VFR weather minimums, visual contact with  the tower is maintained, and a clearance to land is received.  If the aircraft radio fails in flight under IFR, the pilot should  continue the flight by the route assigned in the last ATC  clearance received; or, if being radar vectored, by the direct  route from the point of radio failure to the fix, route, or airway  specified in the vector clearance. In the absence of an assigned  route, the pilot should continue by the route that ATC advised  may be expected in a further clearance; or, if a route had not  been advised, by the route filed in the flight plan.  It is possible for some airports within Class G airspace to  have a control tower (Lake City, FL, for example). Be sure to  check the Chart Supplement U.S. (formerly Airport/Facility  Directory) to be familiar with the airport and associated  airspace prior to flight.  No person may operate an ultralight vehicle within Class A,  Class B, Class C, or Class D airspace or within the lateral  boundaries of the surface area of Class E airspace designated  for an airport unless that person has prior authorization from  the ATC facility having jurisdiction over that airspace. (See  14 CFR part 103.)  Unless otherwise authorized by ATC, no person may operate  an unmanned free balloon below 2,000 feet above the surface  within the lateral boundaries of Class B, Class C, Class D,  or Class E airspace designated for an airport. (See 14 CFR  part 101.)  Regulations regarding unmanned aircraft systems (UAS) are  currently being developed and are expected to be published  by summer 2016 as 14 CFR part 107.  No person may make a parachute jump, and no PIC may  allow a parachute jump to be made from an aircraft, in or  into Class A, Class B, Class C, or Class D airspace without,  or in violation of, the terms of an ATC authorization issued  by the ATC facility having jurisdiction over the airspace.  (See 14 CFR part 105.)  This chapter introduces the various classifications of airspace  and provides information on the requirements to operate in  such airspace. For further information, consult the AIM and  14 CFR parts 71, 73, and 91.  Uncontrolled Airspace  Ultralight Vehicles  Chapter Summary  Parachute Jumps  Unmanned Aircraft Systems  Unmanned Free Balloons  15-11 