8900.1 CHG 604



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Section 1  Evaluate Proposed Adjustments to Task Intervals/Time Limitations for Part 121/135 (10 or More)/91K Continuous Airworthiness Maintenance Program Maintenance Schedules


A.    Program Tracking and Reporting Subsystem (PTRS). For Title 14 of the Code of Federal Regulations (14 CFR) part 91 subpart K (part 91K), use activity codes 3330 and 5330.

B.    Safety Assurance System (SAS). For 14 CFR parts 121 and 135 peer groups, use SAS automation. This section is related to all elements within aircraft technical operations of SAS. This section may be used in conjunction with Custom Data Collection Tools (C DCT).

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3-5063    PURPOSE. This section provides guidance for an aviation safety inspector (ASI) with a Maintenance or Avionics specialty on how to evaluate proposed task interval/time limitation adjustments for maintenance programs. An operator may need to extend or reduce (optimize) its task intervals/time limitations depending on its aircraft utilization, in-service reliability, and environmental conditions operated in. In this section, the term “operator” refers to an air carrier or other entity operating under part 91K, § 91.1411; part 121; or part 135, § 135.411(a)(2). Airworthiness ASIs should use this guidance when evaluating proposed maintenance interval changes of operators without an authorized reliability program.

NOTE:  Operators with a Federal Aviation Administration (FAA)-authorized Maintenance Reliability Program: Reliability programs allow operators to adjust their time limitations without prior FAA acceptance. Specific guidance is provided in Volume 3, Chapter 40, Section 1; Volume 6, Chapter 2, Section 31; and Volume 6, Chapter 2, Section 33.

3-5064    GENERAL.

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A.    Continuous Airworthiness Maintenance Programs (CAMP). The guidance in this section applies to operators who have a CAMP under § 91.1411; part 121, §§ 121.367 and 121.374; or § 135.411(a)(2). An operator must ensure its CAMP is sufficiently comprehensive in scope and detail to maintain its aircraft in an Airworthy condition. An operator must maintain its aircraft, component parts, accessories, and appliances in accordance with the time limits for accomplishing the overhaul, replacement, periodic inspection, and routine checks. The operator’s operations specifications (OpSpecs), management specifications (MSpecs), or a document referenced in these OpSpecs/MSpecs will contain the time limits or standards for determining the time limits.

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B.    Low-Utilization Aircraft. Low utilization is addressed in some Maintenance Review Board Reports (MRBR), and some Original Equipment Manufacturers (OEM) have identified a low utilization as 100 flight‑hours (FH) or less per month. OEMs recommend operators adjust their maintenance program from an FH-based to a calendar-based process for a low-utilization program. When operating a low-utilization aircraft, the operator should contact the OEM for a low-utilization maintenance program as a basis for their program.

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C.    High-Utilization Aircraft. Operators of high-utilization aircraft perform maintenance requirements much more frequently than those aircraft operated within the average time limits for the aircraft projected at type certification. This not only may have a depreciative effect on the aircraft, but it also results in higher operating costs. To ensure that an operator accomplishes maintenance consistent with its operations, the operator should contact the OEM for a high-utilization maintenance program as a basis for their program.

3-5065    ADJUSTMENTS TO TASK INTERVALS/TIME LIMITATIONS. The following intervals may not be extended without approval from the appropriate Aircraft Certification Office (ACO), Maintenance Review Board (MRB) Chairman, or other office of responsibility, as applicable:

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NOTE:  The MRB Chairmen are located at the Aircraft Evaluation Group (AEG) offices (except the Propulsion and APU AEG).

A.    Intervals specified by Airworthiness Directives (AD) (an alternative method of compliance (AMOC) is required when extending intervals specified in an AD).

B.    Life-limited items.

C.    Airworthiness limitation items (ALI).

D.     Certification Maintenance Requirements (CMR) (unless specifically allowed and designated by the CMR document).

E.    Structural sampling periods that the MRBs impose.

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F.    Failure Effect Category 5 and 8 tasks identified or “tagged” in the MRBR (or equivalent) as satisfying a Candidate CMR. These tasks must not be escalated beyond the interval that would otherwise be required by the CMR. Coordination with the OEM may be required. Refer to Advisory Circular (AC) 25-19, Certification Maintenance Requirements.

G.    Critical design configuration control limitations (CDCCL).


A.    References (current editions):

    Parts 91K, 121, and 135.

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    AC 25-19, Certification Maintenance Requirements.

    AC 120-16, Air Carrier Maintenance Programs.

    AC 120-17, Maintenance Control by Reliability Methods.

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    AC 120-79, Developing and Implementing an Air Carrier Continuing Analysis and Surveillance System.

    AC 120-92, Safety Management Systems for Aviation Service Providers.

    AC 121-22, Maintenance Review Boards, Maintenance Type Boards, and OEM/TCH Recommended Maintenance Procedures.

B.    Forms. None.

C.    Job Aids. None.


A.    Determine the Length of the Adjustment.

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1)    The operator must substantiate a data-driven task interval/time limitation adjustment. The length of the adjustment should allow the operator to revise its maintenance schedule without compromising aviation safety. An operator should base its proposed task interval/time limitation adjustment on an analysis of relevant operational data. Regardless of the method used to determine how much data is required, if sampling is used, the data set must result in confidence that the selected data is representative of the entire fleet.
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2)    An operator may propose adjustments to intervals for individual tasks, or for a complete inspection package. However, if an operator requests to adjust intervals for a complete inspection package, an operator must provide a comprehensive justification for the interval adjustments on a task-by-task basis. Justification for adjusting the intervals of individual tasks or inspection packages requires analyzing a representative sampling of operational data relevant to the task. Additional analysis of completed inspections and routine, nonroutine, and teardown report findings generated during those inspections may be required.
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3)    Task interval/time limitation adjustments may be a percentage of an existing time interval for a particular task, or may be designated in hours of time in service, cycles, calendar-time, or some other identifiable increment.
4)    Examine the following documentation to support justification for the proposal, and any pertinent data to its operations identified in subparagraphs 3-5067B5)b) through e) of this section:
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a)    Summary of fleet-wide service experience (hours, cycles, years), time in service, and daily utilization (e.g., high, low, average).
b)    Revised MRBRs for transport category aircraft only if the operator is requesting to use the new MRBR intervals.
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c)    Manufacturer’s information related to the task interval/time limitation (e.g., Service Bulletins (SB), Service Letters (SL), and other in-service reports/resolutions, as applicable).
d)    Recommendations from the operator’s aircraft, engine, propeller, component, or emergency equipment maintenance provider detailing any possible task interval/time limitation adjustments.
e)    Information regarding component removal and replacement activity and vendor repair maintenance records.
f)    Past operating experience (including Continuing Analysis and Surveillance System (CASS) analysis reports) and the maintenance history of the applicable aircraft, engines, propellers, components, or items of emergency equipment.
g)    Overhaul teardown reports from the operator’s aircraft, engines, propellers, or components that show dimensional checks and condition of critical parts. The operator should have operated any engine that it chose for teardown to within 5 percent of the currently approved time in service interval.
h)    Engine oil analysis reports. Review the operator’s oil analysis reports (if applicable) for abnormal wear and recommendations from the lab for follow-up action. Repeat abnormal wear reports may indicate a problem with the operator’s engine maintenance program.
i)    Engine trend monitoring reports. If the operator has a trend monitoring program, review it for abnormalities that would indicate a problem with the operator’s engine maintenance program.
j)    The oil consumption history. This is the history of oil consumption throughout the engine’s operation since its last overhaul.
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k)    Pilot and maintenance reports of mechanical irregularities and the resulting corrective actions.
l)    Routine maintenance tasks that generate no findings. Tasks that generate no findings are as important as tasks that do generate findings.
m)    Routine maintenance tasks that generate findings, which involve structures, zonal areas, and aircraft systems.
n)    Any other data necessary to substantiate the task interval/time limitation adjustment.
o)    Method of monitoring, collection of data and analyzing, specifically with the interval/limitation adjustment over the time period to ensure the anticipated results.

NOTE:  It is the operator’s responsibility to provide the certificate-holding district office (CHDO) with adequate information to justify all aspects of the proposed task interval/time limitation adjustment. The operator must have obtained the information from its own in-service experience and maintenance programs for that particular aircraft type, not from another operator’s experience or programs with that same aircraft or aircraft type.

B.    Evaluate the Proposed Adjustment.

1)    If the operator wants a task interval/time limitation adjustment, it should submit its proposal in writing to the CHDO.
2)    The CHDO must collaborate with the responsible ACO for escalation approval on the applicable items listed in subparagraph 3-5065B. The CHDO must conduct this collaboration with the ACO through the appropriate AEG.
3)    The CHDO must collaborate with the responsible AEG Chairman for escalation concurrence on the applicable items listed in subparagraph 3-5065B.
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4)    Any CHDO questions/issues with the submitted escalation package should be coordinated with their Safety Standards specialist and responsible AEG Chairman.
5)    Depending on the type of aircraft or engine, the items that the CHDO should review may include:
a)    Any information the operator provides that is relevant to the proposed task interval/time limitation adjustment.
b)    Operators may use a change/revision to the MRBR solely to justify a change to their maintenance program as long as the operator has no data contradicting the MRBR change.
c)    Mechanical Interruption Summary Reports (MISR). Review previous MISRs to detect trends or irregularities. This may indicate problem areas in maintenance procedures, operational procedures, or the operator’s training with regards to the reliability of its aircraft.
d)    Service Difficulty Reports (SDR). Query the SDR database for information on the component the operator wants to extend. A high number of reports, failures, or other deficiencies may be a reason to reject a task interval/time limitation adjustment.
e)    AD records. Some ADs may restrict operating an aircraft, engine, propeller, or component past the manufacturer’s recommended task interval/time limitation.
f)    Type Certificate Data Sheets (TCDS). Review the TCDSs for any information related to task interval/time limitation adjustments. The TCDSs may also reference life limits.
g)    Operator’s violation history. Review the operator’s current status and history for any maintenance-related violations, information, and data contained in programs, such as the Enforcement Information System (EIS), Voluntary Disclosure Reporting Program (VDRP), Aviation Safety Action Program (ASAP), etc., when analyzing the risk for the proposed task interval/time limitation adjustment.
h)    Operator’s accident, incident, and occurrence history. If the operator has a history of accidents, incidents, or occurrences related to maintenance issues, this may also be a factor when analyzing the proposed task interval/time limitation adjustment.
i)    Safety Performance Analysis System (SPAS). Use SPAS to review the operator’s surveillance history for items that may indicate the operator’s safety culture and its compliance with regulations. You can identify the operator’s specific areas that may present a greater risk and then analyze safety-critical performance measures.
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C.    Analyze the Findings. You should collaborate with members of the Certificate Management Team (CMT) to analyze the findings from the review of the proposed task interval/time limitation adjustment. You should consult with the Safety Standards specialists and AEG representatives, if necessary, with any questions with the proposals.

NOTE:  Operators may submit a change/revision of an MRBR as justification to change their maintenance program, but must be supported by the operator’s previous operating data and no data contradicting the MRBR change. All submissions should provide data that include maintenance defects/findings, defects resolutions, recurring defects, corrective actions, mitigation actions, risk analysis, and acceptance plans. An operator that cannot provide adequate data to support the submissions may have an underlying maintenance program concern.

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D.    Perform a Risk Analysis and Determine Acceptance/Rejection. Evaluate the risks identified by the operator to determine if the proposed adjustments to task intervals/time limitations do not compromise safety. Evaluate the operator’s application of risk management for risk by using Safety Management System (SMS) principles for the proposed task interval/time limitation adjustment.

1)    Rejection. If your evaluation determines that the operator’s safety culture or operating practices present an unacceptable safety risk, you should reject the proposed task interval/time limitation adjustment.
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2)    Acceptance. If you evaluation determines that the operator can accept any accessed risk without further action, and the operator can provide service with the highest possible degree of safety, you may accept the proposed task interval/time limitation adjustment excluding items in subparagraph 3-5065B.

E.    Debrief the Operator. Debrief the operator by discussing the evaluation results of the proposed task interval/time limitation adjustment. Also discuss any risks identified during the risk analysis.

3-5068    TASK OUTCOMES.

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A.    Acceptance of the Task. Completing this task results in one of the following:

1)    Complete the PTRS Record. For part 91K.
2)    Follow Volume 10 SAS Guidance. Use Module 4 (Chapter 5) and Module 5 (Chapter 6) for parts 121 and 135 peer groups for SAS automation.
a)    This section is related to elements within aircraft technical operations of SAS.
b)    This section may be used in conjunction with C DCTs.
3)    Notify the operator that the FAA accepts the proposed task interval/time limitation adjustment.
4)    After the operator revises OpSpecs D089 (or D088, when issued in conjunction with D075) to reflect the current time limitations document and revision date, issue the appropriate OpSpec to authorize use of the revised time limitations.

B.    Rejection of the Task. Completing this task results in one of the following:

1)    If you determine the proposed task interval/time limitations adjustment is unacceptable, notify the operator by letter that the FAA rejects its proposal.
a)    The letter should include the reasons for the rejection and include the inspection findings.
b)    Return all the documentation the operator submitted.
2)    Initiation of Compliance Action (CA) per Volume 14, Chapter 1.
3)    Information sharing, root cause analysis, corrective action development, and followup.

C.    Document the Task. File all supporting paperwork in the operator’s office file.


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A.    Follow Up on Corrective Actions Taken by the Operator, as Applicable for Part 91K. Periodically review the operator’s maintenance program records for any trends resulting from the task interval/time limitation adjustment.

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B.    Follow Volume 10 SAS Guidance for Parts 121 and 135. Monitor the operator’s maintenance program after any task intervals have been adjusted to ensure the same level of safety and reliability is maintained. The operator should include some type of specific monitoring of any task interval/time limitation adjustment in its CASS program.

RESERVED. Paragraphs 3-5070 through 3-5084.