My friends laugh at me when I ask for a window seat. You\u2019re an\u00a0airline pilot, they say. You have the window seat all the time.<\/p>\n
True enough. But the cockpit, well, that\u2019s work. As a passenger I\u2019m actually free to enjoy the experience\u2014to listen to music or a long-postponed podcast while gazing out at the world below, to remember that it\u2019s still a wonder to look down, not up, at clouds. The window seat is like the best table in a caf\u00e9 on a busy street, except that instead of people-watching, entire cities, oceans, and mountain ranges parade past.<\/p>\n
Still, every once in a while something interferes with that view. Maybe it\u2019s the forehead smudges left by your seat\u2019s previous occupant. Or the little hole that appears in the lower portion of a typical airliner window.<\/p>\n
Hole in the window? The little one, near the bottom, that you perhaps only notice when a hollowed-out snowflake of frost forms near it. This tiny hole is called a breather hole or a bleed hole, and it serves an important safety function.<\/p>\n<\/div>\n
If you look closely at a typical passenger cabin window, you\u2019ll see three panes, typically made of acrylic materials. The purpose of the innermost pane\u2014sometimes called the scratch pane, but I like to call it the smudge pane\u2014is merely to protect the next one.<\/p>\n
The middle pane (with the breather hole in it) and the outer pane are more important. Generally speaking, as an aircraft climbs, the air pressure drops in both the cabin and the outside air\u2014but it drops much more outside, as the aircraft\u2019s pressurization system keeps the cabin pressure at a comfortable and safe level. This means that the pressure inside the aircraft during flight is typically much greater than the pressure outside.<\/p>\n<\/div>\n
The outer two cabin windows are designed to contain this difference in pressure between the cabin and the sky. Both the middle and the outer panes are strong enough to withstand the difference on their own, but under normal circumstances it\u2019s the outer pane that bears this pressure\u2014thanks to the breather hole.<\/p>\n<\/div>\n<\/div>\n
<\/p>\n
As Marlowe Moncur, director of technology \u2028for\u00a0GKN Aerospace, a leading\u00a0passenger cabin window manufacturer, put it to me via email: \u201c[T]he purpose of the small bleed hole in the [middle] pane is to allow pressure to equilibrate between the passenger cabin and the air gap between the panes, so that the cabin pressure during flight is applied to only the outer pane.\u201d<\/p>\n<\/div>\n
In the extraordinarily unlikely event that the outer pane fails, the middle pane takes over. And yes, in that case, there would be a small leak of air through the breather hole\u2014but nothing the aircraft\u2019s pressurization system couldn\u2019t easily cope with.<\/p>\n
Bret Jensen, an aerospace engineering guru at\u00a0Boeing Commercial Airplanes, told me about a separate but related function of the hole: to release moisture from the air gap and stop (most) fog or frost from forming on the window. So when you\u2019re looking out at the clouds and planetary wonders crossing below you, take a moment to give thanks for the breather hole.<\/p>\n<\/div>\n
There\u2019s still the matter of that small but lovely pattern of frost that can form near the breather hole on a long flight. At cruising altitude the temperature of the outside air can be minus 70 degrees Fahrenheit. The frost, according to Moncur, \u201cis caused by condensation of water when cabin air contacts the cold window surface.\u201d<\/p>\n
But what causes that telltale frost pattern? The physics behind it are an interesting question, he says. \u201cThe circular pattern must be a function of window surface temperature, humidity of the cabin air and flow rate through the bleed hole.\u201d<\/p>\n<\/div>\n<\/div>\n
Source: Business Insider<\/p>\n","protected":false},"excerpt":{"rendered":"
My friends laugh at me when I ask for a window seat. You\u2019re an\u00a0airline pilot, they say. You have the window seat all the time. True enough. But the cockpit, well, that\u2019s work. As a passenger I\u2019m actually free to enjoy the experience\u2014to listen to music or a long-postponed podcast while gazing out at the […]<\/p>\n","protected":false},"author":5,"featured_media":122671,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jnews-multi-image_gallery":[],"jnews_single_post":[],"jnews_primary_category":[],"jnews_social_meta":[],"jnews_override_counter":[],"footnotes":""},"categories":[],"tags":[18],"class_list":["post-122650","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","tag-dr-akwasi-osei"],"_links":{"self":[{"href":"https:\/\/citifmonline.com\/index.php?rest_route=\/wp\/v2\/posts\/122650","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/citifmonline.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/citifmonline.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/citifmonline.com\/index.php?rest_route=\/wp\/v2\/users\/5"}],"replies":[{"embeddable":true,"href":"https:\/\/citifmonline.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=122650"}],"version-history":[{"count":0,"href":"https:\/\/citifmonline.com\/index.php?rest_route=\/wp\/v2\/posts\/122650\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/citifmonline.com\/index.php?rest_route=\/wp\/v2\/media\/122671"}],"wp:attachment":[{"href":"https:\/\/citifmonline.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=122650"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/citifmonline.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=122650"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/citifmonline.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=122650"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}