text: Overview Broadly defined, this subdiscipline endeavors to discover and prevent various adverse physiological responses to hostile biologic and physical stresses encountered in the aerospace environment.  Problems range from life support measures for astronauts to recognizing an ear block in an infant traveling on an airliner with elevated cabin pressure altitude. Aeromedical certification of pilots, aircrew and patients is also part of aviation medicine. A final subdivision is the AeroMedical Transportation Specialty. These military and civilian specialists are concerned with protecting aircrew and patients who are transported by AirEvac aircraft (helicopters or fixed-wing airplanes).
  Atmospheric physics potentially affect all air travelers regardless of the aircraft. As humans ascend  through the first 9100–12,300 m (30,000–40,000 ft), temperature decreases linearly at an average rate of 2 °C (3.6 °F) per 305 m (1000 ft). If sea-level temperature is 16 °C (60 °F), the outside air temperature is approximately −57 °C (−70 °F) at 10,700 m (35,000 ft). Pressure and humidity also decline, and aircrew are exposed to radiation, vibration and acceleration forces (the latter are also known as "g" forces). Aircraft life support systems such as oxygen, heat and pressurization are the first line of defense against most of the hostile aerospace environment. Higher performance aircraft provide more sophisticated life support equipment, such as "G-suits" to help the body resist the adverse effects of acceleration, along with pressure breathing apparatus, or ejection seats or other escape equipment.
  Every factor contributing to a safe flight has a failure rate. The crew of an aircraft is no different. Aviation medicine aims to keep this rate in the humans involved equal to or below a specified risk level. This standard of risk is also applied to airframe, avionics and systems associated with flights.