The test plan describes the methodology to determine the inward leakage (i.e. protection factor) of a CBRN respirator for pilots consisting of a visor and an oxygen mask modified to fit a pilot helmet. Three scenarios for the pilot are identified and tests are carried out to meet the typical cases. A first test is performed with air supplied via an external pressure and flow controller (PSU) where the air is assumed to be cleansed from CBRN agents. The tests are conducted seated in the same seating position as the pilot has in the plane. A second test is conducted with pilot air purified by a personal airborne CBRN filter. The test is carried out standing and walking on a treadmill. A third test is carried out with pilot air provided by an external filter fan unit. The test is carried out standing and walking on a treadmill. All three tests are carried out with movements that are adapted to the different cases. Sulfur hexafluoride is used as test atmosphere for the experiments. Parts of the European standard EN 136:1998, Respiratory protective devices - Full face masks - Requirements, testing, marking is used in this test plan.