{"id":5362,"date":"2011-05-27T18:52:08","date_gmt":"2011-05-27T16:52:08","guid":{"rendered":"http:\/\/www.ziserman.com\/blog\/?p=5362"},"modified":"2011-05-27T19:30:11","modified_gmt":"2011-05-27T17:30:11","slug":"4-minutes","status":"publish","type":"post","link":"https:\/\/www.ziserman.com\/blog\/2011\/05\/27\/4-minutes\/","title":{"rendered":"4 minutes&#8230;"},"content":{"rendered":"<p>Comme vous j&rsquo;imagine, j&rsquo;ai \u00e9cout\u00e9 les rapports, suite \u00e0 l&rsquo;analyse des boites noirs de l&rsquo;airbus Paris &#8211; Rio<\/p>\n<p>Ce qui ressort, c&rsquo;est qu&rsquo;apparamment, \u00a0l&rsquo;avion \u00e9tait en \u00e9tat de marche, moteurs op\u00e9rationnels, commandes ok, mais l&rsquo;indicateur de vitesse donnait des informations erron\u00e9es.<\/p>\n<p>Je trouve \u00e7a dingue qu&rsquo;un avion puisse se cracher dans de telles circonstances.<\/p>\n<p>Bon, il y avait de l&rsquo;orage, \u00e7a devait bien secouer.<\/p>\n<p>Mais quand m\u00eame : pourquoi les pilotes n&rsquo;ont ils pas pu redresser l&rsquo;avion ?<\/p>\n<p>4 minutes, le temps de la chute, c&rsquo;est court&#8230; et long \u00e0 la fois : moteurs \u00e0 fond (100% du r\u00e9gime), en tirant sur le manche :<\/p>\n<ul>\n<li>Pourquoi la chute n&rsquo;a pas pu \u00eatre enray\u00e9e ?<\/li>\n<li>Pourquoi n&rsquo;y a-t-il pas d&rsquo;autres calculateurs de vitesse dans un avion \u00e0 ce prix (GPS par exemple) ?<\/li>\n<\/ul>\n<p>Voici un commentaire, post\u00e9 sur <a href=\"http:\/\/www.leparisien.fr\/\" target=\"_blank\">le parisien<\/a>, par un gars connaissant manifestement le sujet :<\/p>\n<blockquote><p>Ce qui est av\u00e9r\u00e9, c&rsquo;est que suite au givrage des sondes de Pitot, l&rsquo;avion a d\u00e9croch\u00e9 pour une raison inconnue, et n&rsquo;a pas pu \u00eatre rattrap\u00e9 par l&rsquo;\u00e9quipage avant l&rsquo;impact avec l&rsquo;oc\u00e9an&#8230; L&rsquo;explication la plus plausible, mais g\u00e9nante est la suivante: Le commandant de bord a pris en charge les operations de la phase de d\u00e9collage jusqu&rsquo;\u00e0 la mise en configuration de vol de croisi\u00e8re \u00e0 38000 pieds sur pilote automatique, puis a c\u00e9d\u00e9 la main aux copilotes&#8230; Ce que le BEA ne dira pas au grand public, c&rsquo;est que pour faire des economies de carburant, la majorit\u00e9 des compagnies a\u00e9riennes ont recours \u00e0 une pratique qui consiste une fois l&rsquo;atitude de croisi\u00e8re atteinte sous pilote automatique \u00e0 d\u00e9caler le centrage des masses de l&rsquo;avion sur l&rsquo;arri\u00e8re, en ballastant du carburant vers l&rsquo;arri\u00e8re. Cela a pour effet de reduire la train\u00e9e de l&#8217;empennage arri\u00e8re. L&rsquo;avion passe alors d&rsquo;une configuration de vol \u00ab\u00a0autostable\u00a0\u00bb avec un empennage arri\u00e8re fonctionnant en d\u00e9portance, \u00e0 une configuration de vol \u00ab\u00a0instable\u00a0\u00bb avec un empennage arri\u00e8re devenant neutre ou porteur. Cette configuration est quasimment impilotable en manuel, seul le pilote automatique est assez pr\u00e9cis pour assurer un vol rectiligne. C&rsquo;est \u00e0 partir de cette configuration que tout s&rsquo;enchaine: Les copilotes pilotent un avion qu&rsquo;ils n&rsquo;ont pas eux m\u00eame ballast\u00e9, ou seulement un des deux y a particip\u00e9. La zone orageuse travers\u00e9e monte \u00e0 une altitude peu courante, avec des turbulences s\u00e9rieuses. Survient alors le givrage des sondes de Pitot \u00e0 une altitude ou l&rsquo;air est habituellement sec, et donc inhabituelle pour ce type d&rsquo;incident. S&rsquo;ensuit le d\u00e9clenchement des alarmes de vitesse, ce qui am\u00e8ne les copilotes \u00e0 repasser en manuel. Ils se font \u00ab\u00a0turbuler\u00a0\u00bb aux commandes d&rsquo;un avion totalement instable, et, r\u00e9flexe de moyennes ou basses couches ou ce type de conditions est plus courant, ils r\u00e9duisent les gaz&#8230; Mais \u00e0 38000 pieds, l&rsquo;air rar\u00e9fi\u00e9 remonte la vitesse de d\u00e9crochage \u00e0 une valeur proche de la vitesse de croisi\u00e8re&#8230; L&rsquo;avion part alors en d\u00e9crochage, et celui ci ne pourra \u00eatre rattrap\u00e9 en poussant le manche pour le faire piquer et reprendre de la vitesse qu&rsquo;une fois les masses recentr\u00e9es en reballastant le carburant vers l&rsquo;avant&#8230; Si cela est bien g\u00e9r\u00e9 et sans d\u00e9lai, pendant le temps n\u00e9cessaire \u00e0 cette op\u00e9ration l&rsquo;avion va chuter \u00ab\u00a0seulement\u00a0\u00bb de 3000 \u00e0 4000 m\u00e8tres avant d&rsquo;\u00eatre r\u00e9cup\u00e9rable.. Et c&rsquo;est cette op\u00e9ration de ballastage que les copilotes vont totalement zapper, en panique \u00e0 cause des alarmes vitesse, cramponn\u00e9s au manche et \u00e0 la commande des gaz d&rsquo;un avion qui ne r\u00e9pond pas&#8230;Le d\u00e9crochage va se poursuivre irr\u00e9m\u00e9diablement jusqu&rsquo;a l&rsquo;impact avec l&rsquo;oc\u00e9an&#8230; Ce qui est d\u00e9rangeant c&rsquo;est de savoir que tous les longs courriers modernes, grace au pilotage g\u00e9r\u00e9 par \u00e9lectronique sont volontairement plac\u00e9s en vol de croisi\u00e8re dans une configuration totalement instable pour economiser du carburant, quitte \u00e0 risquer le gros p\u00e9pin en cas de probl\u00e8me, cisaillement de jet stream par exemple&#8230;<\/p><\/blockquote>\n","protected":false},"excerpt":{"rendered":"<p>Comme vous j&rsquo;imagine, j&rsquo;ai \u00e9cout\u00e9 les rapports, suite \u00e0 l&rsquo;analyse des boites noirs de l&rsquo;airbus Paris &#8211; Rio Ce qui ressort, c&rsquo;est qu&rsquo;apparamment, \u00a0l&rsquo;avion \u00e9tait en \u00e9tat de marche, moteurs op\u00e9rationnels, commandes ok, mais l&rsquo;indicateur de vitesse donnait des informations erron\u00e9es. Je trouve \u00e7a dingue qu&rsquo;un avion puisse se cracher dans de telles circonstances. Bon, [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"footnotes":""},"categories":[2],"tags":[24],"class_list":["post-5362","post","type-post","status-publish","format-standard","hentry","category-e-commerce","tag-hors-sujet"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.2 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>4 minutes... - Ziserman.com<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.ziserman.com\/blog\/2011\/05\/27\/4-minutes\/\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"4 minutes... - Ziserman.com\" \/>\n<meta property=\"og:description\" content=\"Comme vous j&rsquo;imagine, j&rsquo;ai \u00e9cout\u00e9 les rapports, suite \u00e0 l&rsquo;analyse des boites noirs de l&rsquo;airbus Paris &#8211; Rio Ce qui ressort, c&rsquo;est qu&rsquo;apparamment, \u00a0l&rsquo;avion \u00e9tait en \u00e9tat de marche, moteurs op\u00e9rationnels, commandes ok, mais l&rsquo;indicateur de vitesse donnait des informations erron\u00e9es. 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