<story><title>Unexpected cracking found on critical Boeing 737 Next Generation part</title><url>https://komonews.com/news/local/exclusive-unexpected-cracking-found-on-critical-boeing-737ng-equipment</url></story><parent_chain></parent_chain><comment><author>9nGQluzmnq3M</author><text>For context, the 737 NG is previous iteration of the 737 (before the MAX) and among the most popular aircraft ever built, with over 7000 in service.  Grounding this would absolutely cripple the airline industry.&lt;p&gt;However, the NG also has an excellent safety record, and 35000 cycles is equivalent to 5 flights (takeoff &amp;amp; landing) every day for 10 years. So while this may lead to extra checks on older aircraft, it&amp;#x27;s highly unlikely to cause a MAX-style global grounding.</text></comment>
<story><title>Unexpected cracking found on critical Boeing 737 Next Generation part</title><url>https://komonews.com/news/local/exclusive-unexpected-cracking-found-on-critical-boeing-737ng-equipment</url></story><parent_chain></parent_chain><comment><author>newnewpdro</author><text>If a part&amp;#x27;s made of aluminum and undergoes cyclic stress, even staying within its instantaneous modulus of elasticity, it &lt;i&gt;will&lt;/i&gt; eventually crack.&lt;p&gt;Note the aluminum curve in the graph here [0], it &lt;i&gt;never&lt;/i&gt; levels off horizontally.&lt;p&gt;My understanding is this effectively means the modulus of elasticity for aluminum parts is forever diminishing.  Aluminum is a metal that&amp;#x27;s &amp;quot;work hardened&amp;quot;, it&amp;#x27;s basically becoming increasingly brittle the more cyclic stress it experiences.&lt;p&gt;I&amp;#x27;d been told in the past that commercial planes are regularly X-rayed for cracks as part of their maintenance, because of their extensive use of aluminum.&lt;p&gt;None of this should be a surprise except that it&amp;#x27;s supposedly &amp;quot;unexpected&amp;quot; in the pickle fork.  These vehicles have always been high maintenance machines, in order for them to be safe all the structural aluminum must be regularly inspected for cracks, the cracks should be expected and parts replaced as needed.&lt;p&gt;[0] &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Fatigue_limit&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Fatigue_limit&lt;/a&gt;&lt;p&gt;Edit:&lt;p&gt;Out of curiosity I did some digging for photos of this part and more information, this thread delivers some insightful links and citations:&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;www.pprune.org&amp;#x2F;rumours-news&amp;#x2F;625886-737ngs-have-cracked-pickle-forks-after-finding-several-jets.html&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;www.pprune.org&amp;#x2F;rumours-news&amp;#x2F;625886-737ngs-have-crack...&lt;/a&gt;</text></comment>