While most of an aircraft is already sealed off from weather phenomena by nature of being a fully enclosed space, if you look closely, you may spot several rain gutters. Rather than keeping water from pooling anywhere on the vessel, these gutters are mainly used to direct water away from doors and other access points. Unlike other rain gutters, those on aircraft are much smaller and thinner so that they will not interfere with the aerodynamics of the vessel. Nevertheless, these thin gutters are effective at guiding rainwater away from entrances.