14.4 Airworthiness Directives (ADs), Service Bulletins & Logbook Entries

14.4 Airworthiness Directives (ADs), Service Bulletins & Logbook Entries

Quick Answer: Compliance with Airworthiness Directives (ADs) issued under 14 CFR Part 39 is legally mandatory for all aircraft operators under federal law (14 CFR § 39.7). ADs address unsafe conditions and may be Standard (published via NPRM in the Federal Register) or Emergency (immediately effective), with compliance structured as one-time terminating actions or recurring repetitive inspections. In contrast, manufacturer Service Bulletins (SBs) are advisory for Part 91 operators unless incorporated by reference into an AD. Maintenance logbook entries under 14 CFR § 43.9 require a work description, completion date, name of performer, and the signature, certificate number, and rating of the technician approving return to service. Inspection entries under 14 CFR § 43.11 require inspection type, total time in service, signature details, and a specific certified airworthiness statement. Major repairs and alterations require FAA Form 337 in duplicate, using FAA-approved technical data, with one copy submitted to the FAA FSDO within 48 hours.

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Airworthiness Directives (14 CFR Part 39): Regulatory Power & Compliance

Under Title 49 of the United States Code and 14 CFR Part 39, the Federal Aviation Administration (FAA) possesses statutory authority to issue Airworthiness Directives to mandate corrective action when an unsafe condition is discovered.

+-----------------------------------------------------------------------------------------+
|                         14 CFR PART 39 AD REGULATORY FRAMEWORK                          |
|                                                                                         |
|  REGULATORY TRIGGER --> (1) An unsafe condition exists in a product (aircraft, engine,  |
|                             propeller, or appliance); AND                               |
|                         (2) That condition is likely to exist or develop in other       |
|                             products of the same type design. (14 CFR § 39.5)           |
|                                                                                         |
|  LEGAL MANDATE      --> "No person may operate a product to which an airworthiness      |
|                         directive applies, except in accordance with the requirements   |
|                         of that airworthiness directive." (14 CFR § 39.7)                |
|                                                                                         |
|  LEGAL RESPONSIBILITY-> The registered OWNER or OPERATOR is primarily responsible for   |
|                         maintaining the aircraft in an airworthy condition. (91.403a)   |
+-----------------------------------------------------------------------------------------+

Procedural Categories of Airworthiness Directives

1. Standard Airworthiness Directives: Follow standard federal notice-and-comment rulemaking under the Administrative Procedure Act. The FAA publishes a Notice of Proposed Rulemaking (NPRM) in the Federal Register, outlining the proposed corrective action, labor hours, parts cost, and engineering justification. The public and industry have a specified comment period (typically 30 to 60 days) to submit feedback. The FAA then reviews comments, drafts revisions, and issues the Final Rule, which specifies an effective calendar date.
2. Emergency Airworthiness Directives: Issued when an urgent, critical safety threat demands immediate corrective action prior to further flight. Emergency ADs bypass the lengthy NPRM process. They are delivered directly to registered aircraft owners and operators via electronic notification, telegram, or certified mail, and become legally binding immediately upon receipt.

Compliance Lifecycles: One-Time vs. Recurring ADs

• One-Time ADs: Require a specific physical modification, inspection, or part replacement that permanently corrects the unsafe condition. Once complied with and documented in the engine maintenance logbook, no further action is required.
• Recurring (Repetitive) ADs: Require periodic, repeated inspections or servicing at specified operational intervals (e.g., every 50 hours of flight time, every 100 hours, or at each annual inspection). A common powerplant example is a recurring ultrasonic or eddy current inspection of crankshaft propeller flanges or exhaust heat exchangers.
• Terminating Action: An engineering modification, part redesign, or permanent replacement explicitly defined within an AD that, once completed, permanently satisfies and terminates the requirement for further repetitive inspections.
• Alternative Method of Compliance (AMOC): Under 14 CFR § 39.19, an operator or manufacturer may apply to the FAA Aircraft Certification Office (ACO) for approval of an AMOC. An AMOC authorizes a different repair scheme, inspection tool, or compliance timeline than what is published in the AD, provided engineering data demonstrates an equivalent level of safety.

Deciphering the AD Numbering System

The FAA identifies Airworthiness Directives using a standard three-part alphanumeric designation:

                     AD NUMBER BREAKDOWN: AD 2024-14-06 R1
                     
       2024          -         14          -         06          R1
         |                      |                     |           |
     Year Issued         Bi-Weekly Period      Sequence Number  Revision Level
     (Calendar Year)     (14th 2-week block)   (6th AD issued)  (First Revision)

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Service Bulletins (SBs), Service Letters & Service Instructions

Aircraft and powerplant manufacturers (such as Lycoming, Continental, Pratt & Whitney, and CFM International) routinely publish technical service literature to inform technicians of product improvements, service difficulties, and recommended maintenance procedures.

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|                        AD VS. SERVICE BULLETIN LEGAL COMPARISON                         |
|                                                                                         |
|  CRITERIA              | FAA AIRWORTHINESS DIRECTIVE    | OEM SERVICE BULLETIN (SB)     |
|  --------------------- | ------------------------------ | ----------------------------- |
|  Issuing Authority     | Federal Aviation Admin (FAA)   | Engine Manufacturer (OEM)     |
|  Legal Classification  | Federal Aviation Regulation    | Commercial Technical Advisory |
|  Part 91 Mandatory?    | YES - Legally mandatory        | NO - Advisory unless mandated |
|  Part 121/135 Mandatory| YES - Legally mandatory        | YES - If in approved CAMP/Ops |
|  Failure Consequences  | Federal violation; grounded    | Warranty void; civil liability|
+-----------------------------------------------------------------------------------------+

The Mandatory vs. Advisory Legal Distinction

One of the most critical legal principles on FAA examination is the regulatory status of manufacturer Service Bulletins for aircraft operated under 14 CFR Part 91 (general aviation):

• OEM Labeling: Engine manufacturers frequently label their bulletins as "Mandatory Service Bulletin (MSB)" or "Critical Service Bulletin", stipulating compliance within a specific number of flight hours.
• The Part 91 Reality: A private manufacturer cannot enact federal law. For an aircraft operated strictly under 14 CFR Part 91, manufacturer Service Bulletins are ADVISORY recommendations, and compliance is not legally mandatory under federal aviation regulations.
• When a Service Bulletin BECOMES Legally Mandatory:
  1. Incorporation by Reference into an AD: If the FAA references a manufacturer Service Bulletin inside the text of an Airworthiness Directive, that bulletin adopts the full legal force of 14 CFR Part 39.
  2. Airworthiness Limitations Section (ALS): If a service bulletin is incorporated into the FAA-approved Airworthiness Limitations Section of the engine maintenance manual or Type Certificate Data Sheet (TCDS), compliance is mandatory under 14 CFR § 43.16.
  3. Commercial Air Carriers (Parts 121 and 135): Commercial air carriers operating under an FAA-approved Continuous Airworthiness Maintenance Program (CAMP) or approved Operations Specifications are bound to comply with all manufacturer mandatory service bulletins incorporated into their approved manuals.

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Maintenance and Inspection Recordkeeping (14 CFR §§ 43.9 and 43.11)

In aviation maintenance, the physical work and the maintenance record entry are inseparable. Under federal law, maintenance is legally incomplete until properly documented.

1. Maintenance Record Entries (14 CFR § 43.9)

Applies to all maintenance, preventive maintenance, rebuilding, and alteration work (except inspections conducted under Part 91). Every entry must contain four mandatory elements:

+-----------------------------------------------------------------------------------------+
|                       14 CFR § 43.9 MAINTENANCE ENTRY MANDATES                          |
|                                                                                         |
|   1. DESCRIPTION OF WORK --> Detailed account of work performed, or reference to        |
|                              technical data acceptable to the Administrator.            |
|   2. DATE OF COMPLETION  --> Calendar date on which the work was completed.            |
|   3. NAME OF PERFORMER   --> Name of the person performing work (if other than signer). |
|   4. APPROVAL SIGNATURE  --> Signature, certificate number, and rating of the person    |
|                              approving the work for return to service.                  |
+-----------------------------------------------------------------------------------------+

Example 14 CFR § 43.9 Logbook Entry:

"October 14, 2026. Total Engine Time: 1,422.4 hours. Removed Champion REM40E spark plugs. Cleaned, gapped to 0.018 inch, rotated top-to-bottom, and reinstalled with new copper gaskets torqued to 30 ft-lbs. Removed oil filter; cut open and inspected paper pleats, no foreign metal found. Installed new Tempest CH48110-1 filter, lubricated gasket with clean engine oil, torqued to 17 ft-lbs and safety wired. Serviced engine with 8 quarts of AeroShell 15W-50 oil. Performed ground run-up leak check; no leaks observed, normal oil pressure. Engine approved for return to service. /s/ John R. Miller, A&P 3847291."

2. Inspection Record Entries (14 CFR § 43.11)

Applies specifically to 100-hour, annual, and progressive inspections conducted under 14 CFR Part 91. The entry must contain:

1. The type of inspection and a brief description of the extent of the inspection.
2. The date of the inspection and aircraft/engine total time in service.
3. The signature, certificate number, and kind of certificate held by the person approving or disapproving return to service.
4. The Mandatory Certification Statement:
   • If Approved: "I certify that this engine has been inspected in accordance with a [insert type: annual or 100-hour] inspection and was determined to be in airworthy condition."
   • If Disapproved (Found Unairworthy): "I certify that this engine has been inspected in accordance with an annual inspection and a list of discrepancies and unairworthy items dated [insert date] has been provided to the aircraft owner or operator."

[!IMPORTANT] THE DISCREPANCY LIST RULE (14 CFR § 43.11(b)): When an annual inspection is conducted and the engine is found to be unairworthy (e.g., cracked crankcase or cylinder reading 30/80 psi), the mechanic or IA does NOT ground the aircraft or write the discrepancies directly into the permanent logbook as unairworthy defects. Instead, the technician makes the standard logbook entry stating the inspection was performed and disapproved, and provides a signed and dated list of discrepancies and unairworthy items directly to the aircraft owner. The owner is legally responsible for having those discrepancies corrected before flight.

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Retention of Maintenance Records (14 CFR § 91.417)

Federal regulations divide maintenance records into two distinct categories based on required retention duration:

+-----------------------------------------------------------------------------------------+
|                    TEMPORARY VS. PERMANENT AIRCRAFT RECORDS MATRIX                      |
|                                                                                         |
|  RECORD CATEGORY | REGULATORY MANDATE | RETENTION PERIOD                                |
|  --------------- | ------------------ | ----------------------------------------------- |
|  Temporary       | 14 CFR § 91.417a1  | Retained until the work is repeated or          |
|  Records         |                    | superseded, or for 1 YEAR after completion.     |
|                  |                    | (Routine maintenance, 100-hr/annual inspection) |
|  --------------- | ------------------ | ----------------------------------------------- |
|  Permanent       | 14 CFR § 91.417a2  | Retained PERMANENTLY and TRANSFERRED with the   |
|  Records         |                    | aircraft upon sale:                             |
|                  |                    | - Total time in service (engine, prop, airframe)|
|                  |                    | - Life-limited parts current operating status   |
|                  |                    | - Time since last overhaul (all TBO items)      |
|                  |                    | - Current inspection status of the aircraft     |
|                  |                    | - Current status of all applicable ADs          |
|                  |                    | - Copies of all FAA Form 337 major alterations  |
+-----------------------------------------------------------------------------------------+

Airworthiness Directive Compliance Record Requirements

Under 14 CFR § 91.417(a)(2)(v), the permanent engine records must maintain a dedicated, current Airworthiness Directive compliance record. For each applicable AD, the record must detail:

1. The AD number and current amendment/revision date.
2. The date and engine time in service when complied with.
3. The method of compliance (specifying the exact paragraph of the AD satisfied, parts installed, or service bulletin utilized).
4. If the AD is recurring, the next compliance date or time in service when repetitive action is required.

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FAA Form 337: Major Repairs and Major Alterations

Under 14 CFR Part 43 Appendix A, powerplant maintenance operations are strictly classified as either minor or major.

Defining Major Powerplant Repairs and Alterations (Part 43 Appendix A)

• Major Engine Repairs: Structural repairs to the crankcase, crankshaft, or cylinder barrels; repairs to engine mounts; complex internal welding; overhaul of engines equipped with superchargers or reduction gearing; and repairs to internal drive gears.
• Major Engine Alterations: Conversion of an engine model to another model; changes in compression ratio; structural modifications to cooling systems; installation of an unapproved turbocharger system; or replacement of an engine model with a different displacement or horsepower rating.

Form Execution, Approval Data & FSDO Disposition

• Form 337 Execution: Major repairs and major alterations must be executed on FAA Form 337 (Major Repair and Major Alteration) in duplicate.
• Technical Data Requirements: Major repairs and alterations must be accomplished using FAA-Approved Technical Data (such as an FAA Supplemental Type Certificate [STC], an Airworthiness Directive, an FAA Form 8110-3 approved by a Designated Engineering Representative [DER], or an FAA Field Approval documented in Block 3 of Form 337). Standard advisory circulars like AC 43.13-1B represent "acceptable data", but cannot be used as primary approved data for a major alteration without field approval.
• Distribution and Submission Timelines:
  1. The original copy of the completed Form 337 is delivered to the aircraft owner or operator, who must retain it permanently with the aircraft records.
  2. The second copy must be submitted by the approving technician or repair station to the local FAA Flight Standards District Office (FSDO) within 48 hours after the aircraft or engine is approved for return to service.
  3. Exception: If an extended-range fuel tank is installed in the passenger or baggage compartment, a third copy must be kept aboard the aircraft, and the FSDO copy must be submitted within 30 days.

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Independent Prep Note

Independent FAA AMT Powerplant prep by OpenExamPrep. Not sponsored by or affiliated with the Federal Aviation Administration (FAA). Technical data compiled from FAA-H-8083-32B, FAA AC 43.13-1B, and 14 CFR Parts 39, 43, 65, and 91.