Trigger 500 Internal Server Error in PHP and display Apache error page

Question

How can i trigger 500 Internal Server Error or 404 Page Not Found Apache errors in PHP?

For 500 Internal Server Error i have tried

Answer 1

function ISE()
{
  header('HTTP/1.1 500 Internal Server Error', true, 500);
  trigger_error('ISE function called.', E_USER_ERROR);//if you are logging errors?
}

However, you will need output buffering ON to be able to use php header() function after you use any output function like echo.