8900.1 CHG 435

Indicates new/changed information.



Section 1  Evaluate Proposed Adjustments to Task Intervals/Time Limitations for Maintenance Programs


A.    Maintenance: 3330.

B.    Avionics: 5330.

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 Title 14 of the Code of Federal Regulations (14 CFR) part 91K, 91.1411; part 121; and part 135, 135.411(a)(2).

3-5064    GENERAL.

A.    Continuous Airworthiness Maintenance Programs (CAMP). The guidance in this section applies to operators who have a maintenance program under 91.1411; part 121, 121.367 and 121.374; and
135.411(a)(2). An operator must ensure its CAMP is sufficiently comprehensive in scope and detail to fulfill its responsibility to maintain its aircraft in an Airworthy condition that meets its type design or is in a properly altered condition for safe flight. 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.

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 monthly. OEMs recommend operators adjust their maintenance program from a 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.

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.


A.    Operators with a Federal Aviation Administration (FAA)-Approved Maintenance Reliability Program. Maintenance reliability programs allow operators subject to a CAMP under part 121 or part 135 to adjust the time limitations or standards for determining intervals between overhauls, inspections, and checks without prior FAA acceptance. Operators who have an authorized maintenance reliability program should follow that program’s procedures when adjusting task intervals/time limitations.

B.    Restrictions on Task Interval/Time Limitation Extension Adjustments. The following intervals may not be extended without approval from the appropriate Aircraft Certification Office (ACO), or Maintenance Review Board (MRB) Chairman, or other office of responsibility, as applicable:

NOTE:  The MRB Chairmen are located at the Aircraft Evaluation Group (AEG) offices (except the BOS-AEG).

1)    Intervals specified by Airworthiness Directives (AD) (an alternate method of compliance (AMOC) is required when extending intervals specified in an AD).
2)    Life-limited items.
3)    Airworthiness limitation items (ALI).
4)    Certification Maintenance Requirements (CMR) (unless specifically allowed and designated by the CMR document).
5)    Structural sampling periods that the MRBs impose.
6)    MRBR Failure Effect Categories 5 and 8.
7)    Critical design configuration control limitations (CDCCL).


A.    References (current editions):

    Parts 91K, 121, and 135.

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

    AC 120-16, Air Carrier Maintenance Programs.

    AC 120-17, Maintenance Control by Reliability Methods.

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

B.    Forms. None.

C.    Job Aids. None.


A.    Determine the Length of the Adjustment.

1)    You and the operator must collaborate to determine a reasonable length for the task interval/time limitation adjustment. The length of the adjustment should allow the operator to revise its maintenance program or time limitations document without compromising aviation safety. An operator should base its task interval/time limitation adjustment on in-service data collected from a representative sample size of tasks from the operator’s aircraft fleet, which spans all operating environments. The sampling should be derived from at least 10 percent of each aircraft fleet type the adjustment will affect.
2)    An operator may adjust 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 any individual task or inspection package intervals requires analyzing a mutually agreed upon representative sampling of completed inspections and analyzing all routine, nonroutine, and teardown report findings generated during those inspections.
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. Operators must describe in their manual the methods and procedures for calculating task interval/time limitation adjustments.
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:
a)    Aircraft/engine utilization information, a summary of fleet-wide service experience (hours, cycles, years), time in service, and daily utilization (high, low, average).
b)    Revised MRBRs for transport category aircraft only if the operator is requesting to use the new MRBR intervals.
c)    All 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 item 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 followup 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.
k)    Pilot Reports 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.
4)    Any CHDO questions/issues with the submitted escalation package should be coordinated with their regional 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 contradiction 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.

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 regional 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.

D.    Perform a Risk Analysis and Determine Acceptance/Rejection. Perform a risk analysis to determine if the operator can adjust task intervals/time limitations without compromising safety. Evaluate each proposed task interval/time limitation adjustment for risk by using Safety Management System (SMS) principles, as applicable, in AC 120-92.

1)    Rejection. If the risk analysis 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.
2)    Acceptance. If the risk analysis 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 subparagraphs 3-5065B1) through 7).

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.

A.    Complete the PTRS.

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

1)    Rejection. If you determine the proposed task interval/time limitations adjustment is unacceptable, notify the operator by letter that the FAA rejects its proposal. The letter should include the reasons for the rejection. In addition, return all the documentation the operator submitted.
2)    Acceptance. If you determine that the task interval/time limitation adjustment proposal is acceptable and continuous safe operation can be achieved, accomplish the following:
a)    Notify the operator by letter that the FAA accepts the proposed task interval/time limitation adjustment. The operator should then revise its OpSpecs, maintenance program, and/or time limitations document following the procedures outlined in its manual.
b)    Update the appropriate OpSpec/MSpec paragraph, as necessary.


A.    Periodic Checks. Periodically review the operator’s maintenance program records for any trends resulting from the task interval/time limitation adjustment.

B.    Continual Monitoring. 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.