If you wish to contribute or participate in the discussions about articles you are invited to join SKYbrary as a registered user
From SKYbrary Wiki
A numerical technical classification of all the systems and sub systems on an aircraft which is universally used in aircraft engineering and aircraft maintenance. It was developed by the former Air Transport Association (ATA) since renamed Airlines for America (A4A). Following its first issue in 1956, the classification has been adopted industry-wide in aircraft engineering and maintenance documentation. It is based on 100 numbered categories grouped into 'Chapters' within which there are numbered sections and sub sections. This original classification, the ATA ‘spec 100’ was last revised in 1999 and in 2000 it was incorporated with another ATA 'spec 2100' which had been developed to define specifications for electronic technical data interchange into a new ATA 'iSpec 2200' called 'Information Standards for Aviation Maintenance'. At issue, the ATA described 'iSpec 2200' as "a global aviation industry standard for the content, structure, and electronic exchange of aircraft engineering, maintenance, and flight operations information". It consists of a suite of data specifications pertaining to maintenance requirements and procedures, aircraft configuration control, and flight operations.