The zoning of large aircraft is specified by the Airline for America (A4A) in the ATA-100 Specification. These large areas or major zones are further divided into sequentially numbered zones and subzones. A zone is identified by one of three indicators, depending upon whether it is a major zone, major sub-zone, or simply a zone. Major zones are identified by three-digit numbers as follows:
Aircraft Major Zones
| Major Zone | Area |
|---|---|
| 100 | Lower half of the fuselage to the rear pressure bulkhead |
| 200 | Upper half of the fuselage to the rear pressure bulkhead |
| 300 | Empennage, including fuselage aft of the rear pressure bulkhead |
| 400 | Power plants and struts or pylons |
| 500 | Left-wing |
| 600 | Right-wing |
| 700 | Landing gear and landing gear doors |
| 800 | Doors |
| 900 | Reserved for uncommon differences between aircraft types not covered by standard series numbers |
