From The FCC
Radio Maintenance and Repair
You need a commercial radio operator license to repair and maintain the following:
All ship radio and radar stations.
All coast stations.
All hand carried units used to communicate with ships and coast stations on marine frequencies.
All aircraft stations and aeronautical ground stations
including hand-carried portable units) used to communicate with aircraft.
International fixed public radiotelephone and radiotelegraph stations.
You do NOT need a commercial radio operator license to operate, repair, or maintain any of the following types of stations:
Two-way land mobile radio equipment, such as that used by police and fire departments, taxicabs and truckers, businesses and industries, ambulances and rescue squads, local, state, and federal government agencies.
Personal radio equipment used in the Citizens Band, Radio Control, and General Mobile radio services.
Auxiliary broadcast stations, such as remote pickup stations.
Domestic public fixed and mobile radio systems, such as mobile telephone systems, cellular systems, rural radio systems, point-to-point microwave systems, multipoint distribution systems, etc.
Stations that operate in the Cable Television Relay Service.
Satellite stations, both uplink and downlink of all types.
NOTE: Possession of a commercial radio operator license or permit does not authorize an individual to operate amateur radio stations. Only a person holding an amateur radio operator license may operate an amateur radio station.
The FCC does not certify radio repair shops for RC equipment.
From the FCC website.