What is category 19 of ITAR reserved for?

Category XIX is a placeholder for a proposed rule to clarify what constitutes a "gas turbine engine" for export control purposes.

It's primarily intended to alleviate blanket restrictions on components that don't really warrant regulation under the Arms Export Control Act.

From "FR Doc No: 2011-30977"[1] (slightly altered for readability):

  This proposed rule establishes USML Category XIX to cover gas turbine engines and associated equipment currently covered in Categories VI, VII, and VIII.  
  
  The USML identifies engine subcategories in all three of these categories, but there has been confusion concerning the controls in:  
  
  - Category VI: currently lists only "naval nuclear propulsion plants"  
  
  - Category VII: controls both diesel and gas turbine engines under the same general term "engines"  
  
  - Category VIII: controls "military aircraft engines" but not reciprocating engines.  
	
	

[1]: http://www.gpo.gov/fdsys/pkg/FR-2011-12-06/html/2011-30977.h...