These tiny holes are also known as bleed or breather holes. They help to pressurize the cabin and keep windows clear.
Wilbur and Orville Wright—the brothers credited with piloting the first successful flight in history—had to feel the wind on their faces. The modest wooden biplane, made from spruce, ash, and cotton muslin was exposed to outside air. Their historic flight in 1903 only lasted 12 seconds, and they barely reached 10 feet above the ground. Commercial planes today spend the majority of their time in the air. 30,000 feet Temperatures as low as -70° Fahrenheit are not unheard of. To avoid freezing to a crisp, we must have insulated aircraft. We can still book window seats, even though we won’t have the same views as the Wright Brothers in their open air design. You may have noticed the tiny hole on the bottom edge of a window when you sat down in one. It isn’t a mistake. It’s an intentional feature that serves two key purposes—and it even has a special name.
RD Johnson Vice president of safety said, “Those small holes are called breather holes or bleedholes.” Jet LinxTells Travel + Leisure. The windows of an airplane cabin are not made from glass. They’re usually made up of three or more layers of plexiglass, which is actually a plastic. Each window has one bleed-hole, which is usually located in the middle at the bottom. You’ll see that when you place your finger on the hole there is no air coming in or going out. That’s because the hole doesn’t go all the way to the outside—it’s just in the center pane(s) between the inner and outer panes.
Planes not only fly long distances but also cover a large amount of ground when it comes to altitude. After ascending, commercial planes usually cruise around six to seven mile above the Earth before descending. Pressure changes with altitude. Brent Wouters has a masters degree in aerospace before he became CEO of Jet Linx. “At various altitudes, pressure differentials between air in the gap in between the pressurized interior window and the outside change substantially.” Wouters told T+L these holes were necessary to absorb the huge pressure differences. The windows would crack more easily if they were not holed. The hole in the cabin window ensures the inner glass breaks first if it cracks.
Fortunately, cabin windows on airplanes rarely break. The aircraft mechanics inspect the windows regularly and replace them if there are any signs of wear that could be hazardous. Cabin crew is trained to act appropriately if a glass cracks or breaks in mid-flight. In 2024 an All Nippon Airways flight traveling in Japan had to return to its departure airport when a cockpit window cracked mid-flight. Still, the spokesperson for the carrier issued a press release saying “the crack was not a thing that affected the control or pressure of the flight.”
It is also important to maintain windows free of obstructions. Wouters says that “the hole allows moisture to evaporate.” If the hole was closed, moisture would build up from condensation, rendering the window useless. You can thank the tiny holes that keep your bird’s eye view clear and free of condensation.
