The limit of validity (LOV) represents an operational limit based on fatigue test evidence that supports the maintenance program.
The FAA defines the LOV as “the period of time (in flight cycles, flight hours, or both) up to which it has been demonstrated by test evidence, analysis and, if available, service experience and teardown inspections, that widespread fatigue damage will not occur in the airplane structure.” It is further defined as the point in the structural life of an airplane at which there is significantly increased risk of uncertainties in structural performance and probable development of WFD.
Once the airworthiness limitations containing the LOV are approved by the FAA, an airplane may not operate beyond the LOV.
DSG :- Design Service Goal (DSG) is the period of time (in flight cycles/hours) established at design and/or certification during which the principal structure will be reasonably free from significant cracking including widespread fatigue damage.
DSG is generally established at the time of type certification and is NOT intended to limit the life of the structure, or to define the point at which the aircraft cannot continue its operation.
Example – Airbus has developed new, extended service goals (ESG) To justify a further period of operation up to the new ESG, it is necessary to review service experience and re-assess the existing inspection programmes.
This may lead to a modification of the maintenance strategy, including the inspection of additional items or an increased level of surveillance in some areas.
Author- Vander Stone