GR No.17 and GR No.24 have been revised to remove their applicability to aircraft maintained under Part-ML.
Deviations from the Design Approval Holder's Instructions for Continuing Airworthiness (DAH ICA), such as the extension of time between overhaul (TBO) intervals, should be evaluated using a risk-based approach in accordance with ML.A.302.
The risk-based approach should consider aspects such as the operation of aircraft, type of aircraft, hours/years in service, maintenance of the aircraft, compensating measures, redundancy of components, etc.
Alternative tasks or intervals (for example, escalations) to the DAH ICA by the Continuing Airworthiness Management Organisation (CAMO) or Combined Airworthiness Organisation (CAO) do not need to be approved by the Civil Aviation Authority (CAA). Justification of these deviations are to be documented and retained by the CAMO or CAO.
Where an aircraft subject to Part-ML is not used for commercial operations and the owner elects to manage the continuing airworthiness of the aircraft themselves, the owner issues a declaration for the maintenance programme and in this case, no justification of such deviations is required.
Details can be found in Part-ML Paragraph ML.A.302 and AMC1 ML.A.302(c)(3). Owners, operators and approved organisations should ensure they are familiar with the revised regulations as well as the safety implications of any proposed deviations from the DAH ICA.
It is important to note that deviations with respect to tasks classified as mandatory (for example, Airworthiness Directives, requirements specified on the type certificate data sheet, airworthiness limitations) are not permitted.