title: Need to find regex for flight number
body: <p>The airline designator consists of two alphanumeric characters (Any letter from the English alphabet or a digit) followed by an optional letter.  The flight number consists of between 1 to 4 numeric characters (digit) and an optional one letter operational suffix.  All characters are in uppercase. </p>
  
  <p>This is my regex so far:</p>
  
  <pre><code>(?&lt;!([A-Z0-9]))(([A-Z]{2}|[A-Z]\\d|\\d[A-Z])\\s?\\d{3,4})(?:\\D)
  </code></pre>
  
  <p>This doesn't work for the following outputs:</p>
  
  <pre><code>IEL2
  9AI0923
  </code></pre>
  
  <p>Any help is appreciated. Thank you.</p>