Appendix A A-3 A.4 Considerations. The following are special considerations to take into account when reviewing the data used for determining task intervals.
A.4.1 Date of Publication. The inspection program or MPD most recently published (or recommended) by the manufacturer (at the time the AIP is submitted for review by the FAA) should be used as the baseline for comparison purposes, which might not necessarily be the program an operator is currently operating under. This could be relevant if an operator was utilizing an older version of the manufacturer’s program under 14 CFR part 91, § 91.409(f)(3), or if an operator has been operating under an inspection option allowed for under § 91.409(f)(1) or (2). Any items extended or excluded from the baseline program used will require substantiating information to support an adequate justification.
A.4.2 Number of Findings. Just because an inspection does not generate any significant airworthiness findings, that alone is not justification to extend the inspection interval.
Task intervals should be designed to be able to catch any problems before they become safety of flight issues. Take the following basic example: a specific task is set to be repeated every 100 flight hours, but the first issue is not discovered until 500 flight hours.
The next issue is not found until 800 flight hours. This could be used as data to justify a task interval. The task was repeated eight times and only produced a discrepancy twice.
However, note that in the example given, even though the first issue was not found until 500 hours, the next issue was found just 300 hours later. So, based on the data, a task interval of 500 hours would not be appropriate, but an interval that is less than 300 hours could be appropriate with an acceptable margin of safety built in (such as 200 hours).
A.4.3 Criticality. Sometimes, the criticality of the system may dictate that task intervals be designed to give more than one opportunity to find a problem before it becomes a safety of flight issue. So, in the previous example with a failure rate of 1,000 hours, a task interval of 500 hours (two chances) or 325 hours (three chances) could be needed to provide more than one opportunity to catch the failure before it occurred.
Note: This example is only meant to convey a concept, not to provide specific requirements for setting task intervals. Appropriate intervals should be based on a variety of information and more than one or two data points.
A.4.4 Data Source. If the data being used as substantiating information is from aircraft other than the target aircraft (fleet data), the sampled aircraft data presented should be of a similar representation. Ideally, the data should be from an operator’s own fleet, especially if the task interval is based on unique operating conditions, but data from multiple operators can be used as appropriate to the item(s) being extended. The acceptability of fleet data is dependent on how potentially different operating procedures and conditions could affect the inspection items in question. Additionally, the aircraft do not need to be identical, but significant differences in the age and operation may result in the data not being adequate for use as substantiating data. The following information should be considered to gauge the overall acceptability of fleet data used to justify task intervals for specific inspections, items, or tasks.
Appendix A A-4 A.4.4.1 Aircraft time (hours/cycles/years) should be similar to the target aircraft, as applicable to the tasks being extended. Alternatively, if the interval only affects specific components (such as the engine), then the data used should be similarly appropriate.
A.4.4.2 Factors such as dry/humid climate and aircraft storage practices when not being operated. If the interval is based on a specific operating environment, then the data used should be from a representative sample that spans the same environment (e.g., extremely hot and sandy (desert), extremely cold (arctic), extremely corrosive (saltwater areas), etc.). If operators are using specific operational/maintenance practices for justification, then the data should quantify and support how those practices affect the intervals in question.
A.4.4.3 Aircraft specific information, such as manufacturer model, date of manufacture, and serial number specific information.
A.4.4.4 Operational information, such as daily utilization rate (high, low, average) and specific operational history (including periods of prior ownership, if relevant).
A.4.5 Aircraft Utilization. If the AIP justification denotes a specified utilization, then the AIP should specify the expected utilization parameters. The intervals for tasks identified in the manufacturer’s inspection program are usually based on a utilization model that is typical to the industry. An AIP for extremely high or low utilization aircraft should incorporate task intervals appropriate to their operation. Tasking requirements should be addressed on a task-by-task basis to ensure the proper evaluation in regards to the utilization parameters. For low utilization aircraft, ensure that task intervals account for early detection of discrepancies that are sensitive to time (such as corrosion or seal degradation) rather than cycles or flight-hours. Extending task intervals cannot be based on aircraft utilization alone. Data from completed inspection tasks must be considered at a minimum.
A.4.6 Grouped Tasks. If the AIP proposes to extend an entire phase or other collection of inspection tasks, each task within the inspection should be evaluated individually for any potential issues.
A.4.7 Regulatory Requirements. Modification of inspection tasks that affect the airworthiness limitations (AL), component life limits, or ADs do not necessarily have to be excluded, but they would need additional FAA approval outside of the AIP approval process
(e.g., approved alteration, alternative method of compliance (AMOC), etc.) before being able to be included in the AIP. In the same fashion, if any tasks have a regulatory requirement (such as transponder or emergency locator transmitter (ELT) checks), those could not be extended without a corresponding exemption. All of these types of separate approvals should be obtained prior to the submission of the AIP for review and approval by the appropriate FAA office (e.g., Aircraft Evaluation Group (AEG), responsible Aircraft Certification Service office, etc.).
Appendix A A-5 A.4.8 Operational Practices. For calendar intervals, the FAA recognizes that aircraft operational practices (e.g., storage procedures, flight routes/altitudes) can have an effect on the formation of defects, but operational practices should not be used as justification for task intervals. Operational practices cannot be assured and would be very difficult or impossible to monitor or regulate. Instead, operators should focus on data from task findings during the accomplishment of the inspections. If operational practices are having an effect, it will also show up in that data.
A.5 Deficiencies. During the review, the FAA will communicate any deficiencies or concerns it finds to the operator so they can decide to re-submit or modify their proposal.
Operators can mitigate concerns raised during evaluation of the proposed task intervals by providing further data to substantiate the current proposal, moving the specific task(s) in question to an inspection with a more reasonable interval, or modifying the task(s) to reduce the concern.
A.6 FAA Approval. There is not a separate approval process specifically for task intervals alone. This is accomplished and documented by approval of the entire AIP. If the FAA representative does not find the program acceptable, they will provide the operator a letter of denial with the reason the program was not considered acceptable.
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