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.

Aircraft Weighing

Aircraft must be weighed before entering service, to determine the individual mass and CG position. This should be done once all manufacturing processes have been completed. The aircraft must also be re-weighed within four years from the date of manufacture, if individual mass is used, or within nine years from the date of manufacture, if fleet masses are used.

The mass and CG position of an aircraft must be periodically re-established. The maximum interval between one aircraft weigh and the next, must be defined by the operator, but not exceed the four/nine year limits.

In addition the mass and CG position should be re-established either by weighing or calculation when the cumulative changes in the:

·         Dry Operating Mass exceed ± 0.5%

·         CG position exceeds ± 0.5% of the MAC.

An aircraft may be transferred from one JAA operator to another without re-weighing provided both have an approved mass control programme.

Individual or Fleet Mass

When an operator has a number of aircraft of the same type and configuration, he may wish to use the average Dry Operating Mass and CG position of this group of aircraft. The use of fleet mass and CG position is controlled by strict rules to ensure that all aircraft in the fleet stay within the specified limits. If one aircraft exceeds these specified limits, it must be removed from the fleet calculations and individual mass restrictions will apply.