Fix Based Operators are aviation businesses in a particular airport providing different services such as fuel, passenger lounge, pilot briefing, aircraft maintenance & servicing, catering, aircraft management, etc. FBOs may need flight dispatchers to provide operational flight planning, weather briefing, flight scheduling, fuel trip requirements, and others to their clients. Your job is likely the same as air charter companies, however, you'll be handling either your company's or client's aircraft. There are many functions of Fix Based Operators, therefore, your specific responsibilities may vary in every company.
