Aeronautical Radio, Incorporated, or ARINC, is a non-profit organization that sets standards for the avionics industry. In the early 1930's, ARINC issued a standard (referred to as ARINC 404) that specified the form, fit and function of "black box" enclosures and their racking within aircraft. This standard was coined the name ATR for "Austin Trumbull Radio" because of the important work done by Mr. Trumbull. A UAL employee, Trumbull was an early member of the sub-committee and made a significant contribution in the development of the original standard. ATR (or Air Transport Radio as it means today) has become the buzz-word for the pre-specified line replaceable units (or LRU's) and their racking system.

Even though these ARINC-standard enclosures vary in size, shape and function, they all share certain standard dimensions, most notably width (1/4 thru 1 ATR) and length, that make them an ATR case. ARINC 404 has subsequently been revised to become ARINC 404A. Later on, ARINC 600 was issued as a more state-of-the-art standard. One will hear reference of MCU (or Modular Component Unit) that refers to standard height, length and width (1 thru 12 MCU) of these units. Both standards are used today in military and commercial avionics applications.

Churchill Corporation has worked closely in the development of ARINC 404 and ARINC 600 and continues to play a key role in the promotion of standard avionics enclosures. With over 45 years experience, Churchill is a design and manufacturing company that focuses on producing high quality, affordable avionics enclosures and related components for aerospace companies worldwide.