Amarillo Gear & CTI STD-111 does not allow placing the breather inside the fan stack. This placement could potentially draw humid air into the gear case and contribute to oil contamination. The breather should be installed at the end of a vent line running from the gearbox’s designated breather hole to outside the fan stack. The vent line should slope downward at a minimum of 1/2” per foot (25.4mm per 0.31m) to the outside of the fan stack with the breather at the lowest point.  Piping that forms “traps” should be avoided to prevent the vent line from filling with oil or water and preventing the gear drive from breathing.