Also called ATA Spec 100 or ATA 100.
Air Transport Association of America (ATA) standardized the overall
format of the maintenance manuals.
The unique aspect of the chapter numbers is its relevance for all
aircraft.
Thus a chapter reference number for a Boeing 747 will be the same
for other Boeing aircraft, a BAe 125 and Airbus Aircraft.
Each system or system type was assigned a chapter.
For Examples;
• Electrical Power ATA Chapter 24
• Oxygen ATA Chapter 35
• Doors ATA Chapter 52.