FS meaning in Military and Defence ?

A flight surgeon is a military medical officer practicing in the clinical field of aviation medicine. Although the term "flight surgery" is considered improper by purists, it may occasionally be encountered.

Flight surgeons are physicians (MDs or DOs) who serve as the primary care physicians for a variety of military aviation personnel on special duty status — e.g., pilots, Flight Officers, navigators/Combat Systems Officers, astronauts, missile combat crews, air traffic controllers, UAV operators and other aircrew members, both officer and enlisted. In the United States Department of Defense, the Army, Navy, and Air Force all train and utilize flight surgeons. In addition to serving as primary care for military members on special duty status and their families, the U.S. Department of Defense uses flight surgeons for a variety of other tasks.

Aviation medicine is essentially a form of occupational medicine and flight surgeons are tasked with the responsibility of maintaining the military's strict medical standards, especially the even stricter standards that apply to those on flying, controlling or jump (airborne) status. In the U.S military, flight surgeons are trained to fill general public health and occupational and preventive medicine roles, and are only infrequently "surgeons" in an operating theater sense. Flight surgeons are typically rated aviators on flight status (i.e., they log flight hours in military aircraft as a crewmember), but are not required to be rated or licensed pilots, naval flight officers, or navigators/CSOs. They may be called upon to provide medical consultation as members of an investigation board into a military or NASA aviation or spaceflight mishap. Occasionally, they may serve to provide in-flight care to patients being evacuated via aeromedical evacuation, either fixed wing or rotary wing.

The civilian equivalent of the flight surgeon is the Aviation Medical Examiner (AME). Some civilian AMEs have training similar to that of military flight surgeons, and some are either retired military flight surgeons or actively serving flight surgeons in a military Reserve Component.