AC 120-17B

Historical

Advisory circular · Reliability Program Methods—Standards for Determining Time Limitations

A newer version is currentThis is a historical version. AC 120-17B Ed Update is the version in force, approved July 9, 2026.
Approved
December 19, 2018
Last reviewed
August 6, 2024
Cancels
AC120-17A
Family
AC 120-17 · 3 versions
Revision
B
14 CFR parts
91, 119, 121, 135

Guidance, not mandatory unless a rule or AD requires it. DRS record last changed July 10, 2026.

Show pages 27–38

CHAPTER 8. ADMINISTRATIVE

8.1 Regulatory References. Refer to the following 14 CFR parts:

• Part 5.

• Part 91.

• Part 119.

• Part 121.

• Part 135.

8.2 Guidance References (current editions). Refer to the following ACs and orders:

1. AC 00-46, Aviation Safety Reporting Program.

2. AC 00-58, Voluntary Disclosure Reporting Program.

3. AC 20-136, Aircraft Electrical and Electronic System Lightning Protection.

4. AC 20-158, The Certification of Aircraft Electrical and Electronic Systems for Operation in the High-Intensity Radiated Fields (HIRF) Environment.

5. AC 25-19, Certification Maintenance Requirements.

6. AC 26-1, Part 26, Continued Airworthiness and Safety Improvements.

7. AC 120-16, Air Carrier Maintenance Programs.

8. AC 120-42, Extended Operations (ETOPS and Polar Operations).

9. AC 120-59, Internal Evaluation Programs.

10. AC 120-66, Aviation Safety Action Program (ASAP).

11. AC 120-72, Maintenance Human Factors Training.

12. AC 120-77, Maintenance and Alteration Data.

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

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

15. AC 120-93, Damage Tolerance Inspections for Repairs and Alterations.

16. AC 120-97, Incorporation of Fuel Tank System Instructions for Continued Airworthiness into Operator Maintenance and/or Inspection Programs.

17. AC 120-98, Operator Information for Incorporating Fuel Tank Flammability Reduction Requirements into a Maintenance and/or Inspection Program.

18. AC 120-102, Incorporation of Electrical Wiring Interconnection Systems Instructions for Continued Airworthiness into an Operator’s Maintenance Program.

19. AC 120-113, Best Practices for Engine Time In Service Interval Extensions.

8-1

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

21. AC 135-42, Extended Operations (ETOPS) and Operations in the North Polar Area.

22. FAA Order 8040.4, Safety Risk Management Policy.

23. FAA Order 8900.1, Volume 6, Chapter 2, Section 31, Safety Assurance System: Inspect Approved Reliability Program.

24. FAA Order 8900.1, Volume 3, Chapter 40, Section 1, Safety Assurance System: Approving Part 121 and 135 Reliability Programs.

8.3 Other Source References. Refer to the following additional sources:

• Air Transport Association of America (ATA) MSG-3, Operator/Manufacturer Scheduled Maintenance Development, current edition available from:

Airlines for America (A4A) 1301 Pennsylvania Ave NW, Suite 1100 Washington, DC 20004-1707 202-626-4000 http://www.airlines.org

• “E.M.A.C. Maintenance Program Optimization 1” International Air Transport Association (IATA). January 1985.

• “Reliability-Centered Maintenance” F.S. Nowlan, et al, December 1978 (report number AD–A066–579, DD Form 1473, January 1, 1973).

8.4 AC Feedback Form. For your convenience, the AC Feedback Form is the last page of this AC. Note any deficiencies found, clarifications needed, or suggested improvements regarding the contents of this AC on the Feedback Form.

8-2

Page 41OCROpen in PDF

Appendix A APPENDIX A. TASK/INTERVAL ADJUSTMENTS-TOP-LEVEL CHART Task/Interval Note 1 Is the task based on certification or other regulatory requirement?

Note 2 No Is a revision within End +No- the authority of the Reliability Program?

MSI:

Systems Note 4 FEC 5/8 FEC 6/7/9 Zonal/EZAP Structur L/HIRF Operator Programs: Regulatory Authority Appearance/ Note 3 Cleanliness/ or Source Requirement Administrative Tasks Appendix B Appendix C Appendix E Appendix F Appendix G Appendix H Appendix I Notes:

1. Supplemental Type Certificate (STC)-derived instructions for continued airworthiness (ICA) should not be treated any differently than any other task unless the STC holder's ICA documents provide specific instructions for interval management. It is a best practice for operators to coordinate with STC holders by providing product performance feedback during analysis initiatives associated with these designs.

2. Examples include: Airworthiness Directive (AD), Certification Maintenance Requirements (CMR), airworthiness limitation item (ALD), airworthiness limitation (AL) tasks, fuel tank safety (FTS) tasks, Failure Effect Category (FEC) 5 or 8 tasks "tagged" as precluding a CMR, etc.

3. Operators should not rely exclusively on type certificate holder (TCH) assignment of FEC codes. An understanding of the functions under analysis and associated consequences of functional failure is beneficial.

4. Maintenance Significant Item (MSI).

A-1

Page 42OCROpen in PDF

Appendix B APPENDIX B. FAILURE EFFECT CATEGORY (FEC) 5/8 TASKS Note 1. Operators may not delete FEC 5 or 8 tasks. An operator's FEC 5/8 TASK 1 authority to optimize FEC 5 and 8 tasks is restricted to interval changes only. Analysis of FEC 5/8 tasks should be performed by experienced Verify correct FEC code assignment (MRBR). Contact TCH if FEC personnel meeting the competency code is considered minimum per 2.1.d. Incorrect.

Review TCH ICA rules. Do not countermand TCH ICA rules (if applicable). 2 Ensure data selection criteria conforms with guidance in this AC (or as accepted by carrier's CMO).

Consider alternative Is task still Appendix task procedures, No applicable and —No￾ Is task a lube -Yes→ task deletion, aircraft effective? 3 or filter task?

modification, or consult TCH.

Note 2. FEC 5/8 tasks "tagged" or otherwise identified as satisfying a CCMR: TCHs should have Perform analysis of procedures in place to ensure these tasks are not appropriate data: Scheduled Define and susceptible to escalation beyond the SSA interval maintenance defects resulting that would otherwise be required by the CMR. from FEC 8 tasks should be implement sampling Operators desiring to optimize intervals of these carefully analyzed, since CCMR interval established by the SSA during tasks must coordinate with the TCH to ensure the may not reflect hidden failures in-service operational data program for the task. s certification will not be exceeded. Refer to associated with these tasks. 4 AC 25-19.

Is it feasible Does the analysis Note 3. Relative to the targeted substantiate a revised No, or to apply a revised failure mode and original intent. task interval and Inconclusive interval to a fleet remain effective? sub-set for Refer to MSG-3 section 2-3-7.1 sampling?

(Table 2-3-7.1, Criteria for Task Selection) for applicability and safety effectiveness guidance. No Yes Coordinate with the TCH when data from the MSG-3 task analysis is necessary to perform the evaluation. Revise the task interval.

Note 4. Consider communication with TCH to ensure fail-safe design limit is not exceeded.

Schedule a follow-on analysis to validate the task remained effective Retain identity and significance of safety-related tasks such as CMRs, after implementation.

ALIs, AL, FEC 5, and FEC 8.

Note 5. A typical sampling program consists of End a specified number of aircraft, an implementation plan, acceptable performance standards or criteria, performance monitoring and reporting procedures, and a timeline.

B-1

Page 43OCROpen in PDF

Appendix C APPENDIX C. FAILURE EFFECT CATEGORY (FEC) 6/7/9 TASKS FEC 6/7/9 Task Verify correct FEC code assignment (MRBR). Contact TCH if FEC code is considered Note 1. Relative to the targeted incorrect.

failure mode and original intent.

Refer to MSG-3 section 2-3-7.1 Is task a Lube or Filter task? Yes→ Appendix D (Table 2-3-7.1, Criteria for Task Selection) for applicability and safety effectiveness guidance.

No Coordinate with the TCH when data from the MSG-3 task analysis is Ensure data selection criteria conforms with guidance in necessary to perform the evaluation. this AC (or as accepted by carrier's CMO).

Note 3. A typical sampling program Consider alternative Is task still consists of a specified number of task procedures, applicable and aircraft, an implementation plan, acceptable performance standards or task deletion, aircraft effective? 1 modification, or consult TCH. criteria, performance monitoring and reporting procedures, and a timeline.

Define and implement Perform analysis of appropriate data. sampling program for the task. 3 Does the Is it feasible analysis Note 2. Based on current substantiate a No, or to apply a revised performance standards revised task interval Inconclusive interval to a fleet system. and remain sub-set for effective? 2 sampling?

No, or Inconclusive Is the Revise task anticipated scope, type, -Yes- impact to operational and/or interval. performance acceptable?

No Based on risk, schedule a follow-on analysis to validate the task remained effective after implementation.

End C-1

Page 44OCROpen in PDF

Appendix D APPENDIX D. LUBE/FILTER TASKS Note 1. Consideration volumes, rates of usage or deterioration, and the unit's ability to perform its intended function. Do not assume variables are constant. It is possible that at some Lube/Filter Tasks 1 point, rates may accelerate.

Verify correct FEC code assignment (MRBR). → Contact TCH if FEC Note 2. Relative to the targeted code is considered failure mode and original intent. incorrect.

Refer to MSG-3 section 2-3-7.1 Ensure data selection criteria conforms with guidance in (Table 2-3-7.1, Criteria for Task this AC (or as accepted by carrier's CMO).

Selection) for applicability and safety effectiveness guidance.

Coordinate with the TCH when data from the MSG-3 task analysis is Is task still Consider alternative necessary to perform the evaluation. applicable and task procedures, effective? 2 task deletion, aircraft modification, or consult TCH.

Note 3. The selected interval should be based on the consumable's usage rate, the amount of consumable in the system (if applicable), and performance deterioration characteristics.

Typical operating environments and climatic conditions are to be considered when assessing the deterioration characteristics.

Consider primary and peripheral purpose of consumable materials (e.g., does it also provide a means of compliance with the operator's aircraft corrosion objectives).

Note 4. If alternative material (lubricants, filter elements, etc.) are considered to extend an interval, consider compatibility of alternative Perform analysis of appropriate data.

products with existing system features and design performance. Caution should be exercised for material compatibility (e.g., lithium grease and compatibility).

Does the analysis Revise task substantiate a •Yes→ scope, type, revised task interval and/or and remain interval. 3 effective? ½ Initiate change Does data in consumable +Yes- analysis support introduction material. ot alternative consumable material? 4 No End D-1

Page 45OCROpen in PDF

Appendix E APPENDIX E. ZONAL/ENHANCED ZONAL ANALYSIS PROCEDURE (EZAP) Zonal/EZAP Tasks 1 Review TCH ICA rules. Do not countermand TCH ICA rules (if applicable). 2 Ensure data selection criteria conforms with guidance in this AC (or as accepted by carrier's CMO).

Consider alternative Is task still task procedures, •No- applicable and task deletion, aircraft effective? 3 modification, or consult TCH.

yes Consider density, type and function (constant and intermittent current loads) of wiring and interconnection systems in the zone under review.

Will interval or task Does the zone scope adjustment maintain contain L/HIRF •Yes acceptable levels of accumulated and protection? s potentially flammable contamination? * Analysis of L/HIRF and zonal routine task Ensure the analysis includes review of TCH cross findings should take into consideration reference appendices that correlate systems/structures maintaining L/HIRF protection. 6 tasks satisfied by zonal tasks (as applicable).' Perform analysis of appropriate data.

Will the interval and/or task scope adjustment maintain acceptable levels of L/HIRF protection? & Is the task used Does the analysis -Yes- to take credit for DT for repairs or *Yes- task interval and remain substantiate a revised alterations? effective?

Review previous repair or No alteration records to identify repairs or alterations which may No require individual tracking based No on new interval.

If applicable, Revise task track repairs scope/type and alterations and/or separately interval.

End E-1

Appendix E Note 1.

- Consider aircraft structure, systems, and installations within the zone to ensure unintended degradation or loss of function will not occur.

- Traceability o f revisions to approved electrical wiring interconnection system (EWIS) instructions for continued airworthiness (ICA) to include task, intervals, procedures, protections, and cautions must be maintained.

- As a pplicable, operators must apply any additional procedures or restrictions based on their compliance document requirements.

- Deletions of EWIS tasks must be approved by the FAA oversight office via the operator’s principal maintenance inspector (PMI).

Note 2.

Example:

Some zonal tasks may partially satisfy damage tolerance requirements which must be performed at originally-established l imits after a certain fatigue threshold. Intervals may be escalated prior to that threshold, but must be adjusted to the original levels at the threshold.

Note

3.

- Relative to the targeted failure mode and original intent.

- Refer t o Maintenance Steering Group – 3rd Task Force (MSG -3), volume 1, section 2-3-7 .1 (Table 2-3-7.1, Criteria for Task Selection) for applicability and safety effectiveness guidance.

Note 4. This evaluation doesn’t necessarily include the concept of actually measuring contamination or accumulation r ates. However, each task adjustment should be sufficiently substantiated, which includes whether the desired results will continue to be achieved at the revised interval. Refer to AC 25-27, AC 120-94, and AC 120-102 for additional information on contaminants.

Note

5. Lightning/High Intensity Radiated Fields (L/HIRF) protection may include:

- Wires, shields, connectors, bonding straps, raceways between connectors.

- L/HIRF p rotection within conduit or heat shrink or other covering.

- Non-metallic structure with conductive mesh and/or antistatic coatings.

Note

6. Consider:

- The environment and effects of corrosive produces, condensation, temperature, and vibration on the protection.

- Increased susceptibility to damage during maintenance or operations (e.g., where connectors could be stepped on, or effects of deicing fluid on a connectors during winter operations).

Note 7. Awareness of these relationships support a quality analysis. Zonal working groups may have modified zonal intervals to accommodate these interfaces.

Note 8.

- For example, findings associated with bonding straps, lightning wicks, tank plate wiring/connector bonding, etc.

- Ensure unintended consequences such as Environmental Deterioration (ED) or Accidental Damage are not introduced due to frequency of access/egress.

E-2

Page 47OCROpen in PDF

Appendix F APPENDIX F. STRUCTURE Note 1. General Information:

- The actuating portions of items such as landing gear, flight controls, doors, etc. are treated under systems analysis. Structures Tasks

- Dynamic components such as hinge bearings are treated as system component.

- Attachment fittings of the actuators to the airframe are treated as a structure analysis. Ensure data selection criteria conforms with guidance in

- Structure-to-structure attach points, not this AC (or as accepted by carrier's CMO).

otherwise associated with an aircraft system

(e.g., pylon attach fittings and diagonal braces) that feature bearings are be treated as Ensure TCH ICA structure. document

- Special consideration should be given to Does the TCH ICA guidance is analysis associated with attach points to structure since the structural analysis may not provide full consideration for wear and document contain specific instructions for structures program adjustment? Yes → section 9), (e.g., MPD followed deterioration. These analyses should be and...

compared with the appropriate system analysis, as applicable.

- Wear is typically found in/at bushings, bearings, stops, latches, locks, tracks, guides, Ensure data selection criteria conforms with guidance in cams, rollers, cables, pulleys, or floors. Wear can this AC (or as accepted by carrier's CMO).

influence loads and strength, lead to inaccurate positioning and adverse free play or change resistance to environmental deterioration.

Wear can be systematic for parts intended to be Is task still Consider alternative task in contact, or random for parts that should applicable and normally not come in contact or should not be effective? 2 task deletion, aircraft procedures, subjected to relative motion. modification, or consult TCH.

- Non-metallic structure is susceptible to damage and/or deterioration such as disbonding and delamination. These structures are not normally susceptible to Perform analysis of appropriate data.

degradation due to the environment

(e.g., corrosion). Special consideration should be given for non-metallic structure and any uniqueness associated with applicable damage sources.

Does the Appendix H. Follow End. analysis Is the task AD requirements for No change to task substantiate a a corrosion Yes Is the CPCP -Yes→ interval type, scope, or revised task interval detection AD-mandated? adjustments.

interval. and remain task?

effective? 3 Note 2.

Ensure

- Relative to the targeted failure mode and substantiating data original intent. - Refer to MSG-3 section 2-3-7.1 credit for DT for repairs or Is the task used to take accounts for (Table 2-3-7.1, Criteria for Task Selection) for alterations? previous findings and corrective applicability and safety effectiveness guidance. actions. 4

- Coordinate with the TCH when data from the MSG-3 task analysis is necessary to perform Note 4. The program is expected to control the evaluation. corrosion to Level 1 or better. Initial programs assume an aircraft is operated in Review previous repair or alterations a typical environment. If the analysis Note 3. Consider all damage sources: records to identify repairs or alterations reflects a trend in corrosion defects that Environmental Damage (ED) (corrosion, which may require individual tracking exceed Level 1, the corrosion control stress corrosion, delamination, disbonding, based on new interval. program for the affected area should be etc.); Fatigue Damage (FD); Accidental reviewed by the operator with the Damage; and Wear Damage (WD). objective to ensure Level 1 or better.

Revise task scope/type and/or End accomplishment interval.

F-1

Page 48OCROpen in PDF

Appendix G APPENDIX G. LIGHTNING/HIGH INTENSITY RADIATED FIELDS (L/HIRF) TASKS Note 1. Coordination with OEM is L/HIRF Task ' recommended. L/HIRF protection may include:

- Wires, shields, connectors, bonding straps, raceways between connectors.

- L/HIRF protection within conduit or Review TCH ICA heat shrink or other covering. rules.

- Non-metallic structure with conductive mesh and/or antistatic coatings.

Ensure TCH ICA rules are followed, if applicable.

Ensure data selection criteria conforms with guidance in this AC (or as accepted by carrier's CMO).

Perform analysis of appropriate data. 2 Note 2: Analysis should consider:

- The environment and effects of corrosive products, condensation, temperature, and vibration on the protection. Does the

- Susceptibility of damage during maintenance or analysis operations (e.g., where connectors could be stepped substantiate a task interval and/or scope revision that -No on, or effects of deicing fluid on a connector during maintains acceptable levels winter operations. of L/HIRF

- Scheduled maintenance findings associated with protection?

bonding straps, lightning wicks, tank plates wiring/ connector bonding, etc.

Yes Revise task scope, type, and/or interval.

End G-1

Page 49OCROpen in PDF

Appendix H APPENDIX H. OPERATOR PROGRAMS AND APPEARANCE Note 1. This decision tree applies to Operator Program tasks developed and implemented by the operator, such as: and Appearance Tasks 1

- Tasks that support other tasks;

- Administrative support tasks;

- Branding/image objectives; and standards established by the operator. - Cabin appearance and cleanliness task a response, Is this Appendix A; or other defined or is it otherwise related to a deficiency in the Yes→ analysis process operator's CAMP?

No Based on risk, determine the data set and analysis needed to evaluate the proposed change Does the Is the analysis anticipated impact +No- substantiate a acceptable? revised or deleted task?

No Yes Yes Delete or revise task scope, type, and/or accomplishment interval.

End H-1

Page 50OCROpen in PDF

Appendix I APPENDIX I. REGULATORY SOURCED REQUIREMENTS Regulatory Sourced Task ' Note 1. Examples include:

AD, CMRS, ALI, AL, and FTS tasks.

Does the Ensure regulatory regulatory authority/ authority source source requirement contain specific YesT requirements are instructions for task followed.

adjustment?

No Ensure data selection criteria conforms with guidance in this AC (or as accepted by carrier's CMO).

Note 2. Relative to the targeted failure mode and original intent.

Does Refer to MSG-3 section 2-3-7.1 analysis substantiate (Table 2-3-7.1, Criteria for Task adjustment of the task Selection) for applicability and safety interval and remain effectiveness guidance. No effective? 2 Coordinate with the TCH when data from the MSG-3 task analysis is necessary to perform the evaluation.

Submit proposal to the regulatory authority/source requirement holder.

Was approval obtained from the regulatory authority/ source requirement No holder?

Yes Revise task as approved.

End I-1