HttpException: Why doesn't Application_Error in my global.asax catch the "Request Timed Out" exception

When a page times out(Request Timed Out) in my application, the Application_Error sub in my Global.asax is not being fired. I have custom code in place to redirect an user a custom error page when application errors occur. Why is 开发者_StackOverflow社区the HttpException not being captured?

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EDIT: Sorry I misunderstood.

If you are having a timeout request ASP.NET kills the thread because the runtime will throw a ThreadAbortException which will not be caught be global.asax Application_Error