Section 6 – Humdity:
Category A – Standard Humidity Environment
Equipment intended for installation in civil aircraft, non -civil transport aircraft and other classes, within environmentally controlled compartments of aircraft in which the severe humidity environment is not normally encountered.
Category B – Severe Humidity Environment
Equipment installed in zones not environmentally controlled may be required to be operated under conditions such that it is subjected to a more severe atmospheric humidity environment for periods of time in excess of that specified for the standard humidity environment.
Category C – External Humidity Environment
Equipment may be required to be operated under conditions such that it is subjected to direct contact with outside air for periods of time in excess of that specified for the standard humidity environment.