Aircraft Structure Zoning System

Zoning of large aircraft is specified by the Air Transport Association of America in the ATA-100 Specification.
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:
Major Zone                                       Area
 No.                                 
100              Lower half of the fuselage to the rear pressure bulkhead (below the main cabin deck).
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.

The standard series is from 100 to 800 and the special series numbers are in the 900 bracket. \

Aircraft Maintenance Requirements

Aircraft maintenance requirements fall into two main categories:

•   Scheduled – where we know, in advance, when and what will cause the maintenance to be due.
•  Unscheduled – where we do not know when the  maintenance will be due although we may be able to anticipate a certain number of unscheduled maintenance events over a period of time from the analysis of reliability records.

In both of the above cases certain factors or events trigger maintenance as illustrated.

Consider, first, the factors which trigger scheduled maintenance.  The primary trigger is the MAINTENANCE SCHEDULE itself, this is usually part of the MAINTENANCE PROGRAMME.  The schedule must be approved by the Airworthiness Authority.

The maintenance schedule or programme specifies:

• which maintenance tasks are to be carried out and.
• when they are to be carried out.

The specification of WHEN is stated in periods between maintenance events measured in:

•   days, weeks, months or years (calendar time).
•  aircraft flying hours.
• engine or propeller hours.
•  number of landings.
•  number of cycles (eg engine start/stop cycle or pressurisation cycle).

The time related intervals may be combined so, for example, a maintenance task may have to be carried out every 50 flying hours or 62 days whichever is the sooner.