AD/CESSNA 170/79 - Crew Seat Back Cylinder Lock Modification

The core technical problem targeted by this AD is structural failure or cracking of the crew seat back cylinder lock assembly at its aft end. The AD’s Background links this mechanical failure to flight safety consequences: uncontrolled or abrupt movement of the seat back, backward collapse during flight, a possible abrupt aircraft pitch-up if a pilot remains holding the yoke, and difficulty exiting the aircraft from an aft passenger seat after landing (Background). The AD therefore addresses an identified airworthiness hazard by mandating physical modification or inspection and corrective action.

Key technical elements in the AD are expressed through modification kits and service bulletin procedures. The AD distinguishes three kit states:

• No retrofit kit (neither MK172-25-10A nor MK172-25-10B installed), in which case the AD requires installation of MK172-25-10C or fabrication/installing a steel lock rod/bar per specific Cessna Service Bulletins (Requirement 1);
• MK172-25-10A or MK172-25-10B already installed, in which case the AD requires an installation inspection and possible corrective action in accordance with SB04-25-01 Rev 4 (Requirement 2);
• MK172-25-10C, which the AD identifies as the preferred retrofit if A/B are not present (Requirement 1).

The AD is prescriptive about documentary sources: it requires adherence to Cessna Single Engine Service Bulletin SB04-25-01 Revision 4 dated 26 December 2006 for MK172-25-10C installation, and allows fabrication and installation of a steel lock rod/bar only if done following Cessna Single Engine Service Bulletin SB04-25-02 (Revision 1 dated 17 October 2005 or Revision 2 dated 5 June 2006) (Requirement 1). For aircraft with previous kits (A or B), the inspection and corrective action must follow SB04-25-01 Revision 4 (Requirement 2).

Timing and prioritisation are central concepts. The AD assigns differing urgency depending on the aircraft’s time-in-service (TIS) as at the AD effective date: higher TIS triggers shorter compliance window (over 1,000 hours , 4 months; 501-1,000 hours , 8 months; 0-500 hours , 12 months) (Compliance). For aircraft that already have kits A or B installed, the AD sets an immediate inspection window (30 days) and requires remediation before further flight if discrepancies are found (Compliance, Requirement 2).

Record-keeping is another embedded concept. If an aircraft has MK172-25-10A/B and the inspection finds no discrepancy, the operator must make a log book entry showing compliance, and no further action is required (Requirement 2(ii)). The AD therefore ties a maintenance action to an administrative record that evidences compliance.

Finally, the AD cross-references FAA AD 2007-05-10 and Cessna service bulletins, meaning the detailed technical method and acceptance criteria are located in those referenced documents (Note). The AD uses those external technical documents as the operative instructions the operator must follow.

The AD’s applicability is narrowly defined in the AD table. It applies to Cessna 172R and 172S aeroplanes within specific serial number ranges: Cessna 172R serial numbers 17280001 through 17281262, and Cessna 172S serial numbers 172S8001 through 172S9994 (Applicability). The AD title references Cessna 170, 172, F172, FR172 and 175 Series aeroplanes, but the formal “Applicability” field lists the 172R and 172S serial number blocks; practitioners should rely on the formal Applicability entry when determining whether a particular airframe is covered.

Practically, the primary economic actors affected are owners and operators of the listed aircraft, and the maintenance organisations or engineers who must carry out the installation, fabrication or inspections specified. The AD requires either installation of a new kit (MK172-25-10C), fabrication and installation of a steel lock rod/bar following a Cessna service bulletin, or an inspection and corrective actions where earlier kits MK172-25-10A or MK172-25-10B are already installed. Those actions impose labour, part and potentially specialist fabrication costs on the aircraft owner/operator; the AD text itself prescribes the actions but not who funds them , commercial responsibility ordinarily rests with owners/operators, as they must permit and ensure the work is done to comply with the AD (Requirement 1; Requirement 2).

Maintenance providers and certifying staff are affected in that they must follow the exact Cessna Single Engine Service Bulletins named in the AD for the installation, fabrication and inspection steps (SB04-25-01 Rev 4; SB04-25-02 Rev 1 or 2) (Requirement; Note). If a maintenance organisation is to sign off compliance in the aircraft log book (Requirement 2(ii)), that organisation carries the professional responsibility to ensure the inspection was correctly conducted and the log book entry correctly records compliance.

Regulators are implicated through issuance and monitoring of the AD. The AD is signed by David Villiers, Delegate of the Civil Aviation Safety Authority (CASA) (signature block), indicating CASA as the issuing authority. The AD references FAA AD 2007-05-10 and Cessna Service Bulletins as part of the technical regime the CASA AD requires operators to follow. The AD’s effective date of 11 April 2007 sets the clock for the compliance windows (Compliance).

Finally, the AD implicitly affects passengers and crew safety by seeking to mitigate the risk of seat-back collapse and associated flight-safety consequences; the AD’s Background explains the safety hazard the mandatory actions seek to prevent (Background).

Duties:

• Confirm applicability: The operator must first determine whether their aircraft falls within the serial number ranges specified for Cessna 172R (17280001-17281262) or 172S (172S8001-172S9994) in the AD’s Applicability field (Applicability).
• If neither MK172-25-10A nor MK172-25-10B is installed: For each crew seat (pilot and co-pilot), the operator must either install Modification Kit MK172-25-10C or fabricate and install a steel lock rod/bar following the procedures set out in the cited Cessna Service Bulletins (Requirement 1). The AD specifies that installation is to follow Cessna Single Engine Service Bulletin SB04-25-01 Revision 4 dated 26 December 2006 for MK172-25-10C installation, or SB04-25-02 Revision 1 or 2 for fabricating and installing a steel lock rod/bar (Requirement 1).
• If MK172-25-10A or MK172-25-10B is already installed: For each crew seat, the operator must perform an installation inspection in accordance with SB04-25-01 Revision 4 (Requirement 2(i)). If no discrepancies are found, the operator must make a log book entry showing compliance with the AD and no further action is required (Requirement 2(ii)). If discrepancies are found, the operator must make all necessary corrective actions per SB04-25-01 Revision 4 (Requirement 2(iii)).
• Observe compliance windows: For aircraft without A/B installed, the operator must comply within the time window determined by the aircraft’s time-in-service at the AD effective date: over 1,000 hours , within 4 months; 501-1,000 hours , within 8 months; 0-500 hours , within 12 months (Compliance). For aircraft with A/B already installed, the inspection must be done within 30 days after the effective date, and any corrective work required by the inspection must be completed before further flight (Compliance; Requirement 2).

Rights (as expressed or implied by the AD text):

• Choice of method for compliance in certain circumstances: Where MK172-25-10A/B are not present, the AD permits either installing MK172-25-10C or fabricating and installing a steel lock rod/bar, so long as the fabrication follows the specified Cessna Service Bulletin (Requirement 1). That gives operators a technical choice between using the supplied kit or fabricating a component in accordance with specified procedures.
• Evidence of compliance: If the inspection for aircraft with MK172-25-10A/B finds no discrepancies, the operator has the right to make a log book entry showing compliance and thereby conclude AD obligations for that aircraft (Requirement 2(ii)). The log book entry serves as documentary proof of compliance under the AD text.

Procedural constraints:

• The AD prescribes specific authoritative versions of the Cessna Service Bulletins that must be followed (SB04-25-01 Rev 4, SB04-25-02 Rev 1 or 2). Compliance must be in accordance with those versions and dates as referenced (Requirement; Note).
• The AD imposes “before further flight” constraints for rectifying discrepancies discovered on inspection for aircraft with kit A/B installed (Requirement 2(iii); Compliance). That creates an operational constraint , aircraft may not resume flight until corrective action per the AD is complete.

Administrative detail:

• The effective date, 11 April 2007, is the reference point for all compliance periods (Compliance). The AD is signed by a CASA delegate, which is the issuing authority for the directive (signature block).

The AD text does not specify penalties, enforcement mechanisms or appeal processes within its body. It therefore sets out obligations and documentary requirements but leaves enforcement and any sanctions to the broader regulatory regime or CASA practice, which the AD does not itself elaborate (see Penalties and enforcement section below).

The AD text itself does not set out statutory penalties, fines or specific enforcement procedures. It prescribes mandatory actions and timelines, but contains no penalty clause or enforcement schedule in the supplied text. The AD language uses imperative instructions (“install”, “perform”, “make all necessary corrective actions”, “make a log book entry”) and specifies compliance timelines, which function as regulatory obligations; however the document does not enumerate the legal consequences of failure to comply within the AD text provided.

What the AD does show about enforcement context:

• It is issued and signed by a Delegate of the Civil Aviation Safety Authority (David Villiers), which indicates the issuing regulator and the official promulgating the requirement (signature block, 9 March 2007). That identifies the regulatory origin of the AD, but not the enforcement steps.
• The AD establishes documentary evidence of compliance by requiring a log book entry where an inspection finds no discrepancies (Requirement 2(ii)). Such a log book entry is typically the primary record used by compliant operators to evidence that the AD’s requirements have been met.

Risks of non-compliance, as implied by the instrument:

• The AD links the corrective work to an airworthiness hazard (seat-back cylinder lock failure could cause backward collapse and abrupt pitch-up) (Background). Operators who do not carry out the required actions would therefore continue to operate aircraft with a known hazard identified in the AD.
• The AD imposes “before further flight” constraints for aircraft with kit A/B when discrepancies are found on inspection, implying immediate grounding of affected aircraft until corrective action is carried out (Requirement 2(iii); Compliance). That operational constraint functions as an immediate enforcement mechanism in practice: an aircraft with a discovered discrepancy may not be flown until the defect is corrected as required.

What the AD does not say:

• It does not specify civil penalties, criminal sanctions, deregistration, or suspension processes. It does not include a compliance-audit mechanism or specify how CASA will verify adherence. There is no mention of timelines for follow-up inspections or reporting to CASA beyond the log book entry mandated in one scenario.
• It does not state appeals processes or review mechanisms for operators disputing the AD’s application to a particular airframe.

For legal practitioners advising clients, the AD should be treated as a mandatory technical requirement that must be complied with according to the AD’s terms and timelines. The AD itself provides the prescriptive actions and documentary proof (log book entry) in some cases, but an operator seeking clarity on enforcement or sanctions would need to consult CASA’s broader regulatory framework or guidance, which is not contained in the AD text supplied.

This AD cross-references external regulatory and manufacturer documents rather than reproducing detailed technical procedures. The AD explicitly refers to FAA AD 2007-05-10 and to specific Cessna Single Engine Service Bulletins (SB04-25-01 and SB04-25-02, with precise revisions and dates) as the operative technical instructions for installation, fabrication and inspection (Requirement; Note). The AD therefore operates by incorporating those documents by reference as the detailed method for compliance.

Interaction with maintenance and aircraft records:

• The AD requires a log book entry in the scenario where an inspection (for aircraft with MK172-25-10A or MK172-25-10B installed) finds no discrepancies (Requirement 2(ii)). That creates a direct interaction with aircraft maintenance records and implies that an aircraft’s log book is the documentary vehicle for demonstrating compliance with this AD. The AD does not specify the form of the log book entry beyond that it shows compliance, but the AD’s requirement links to record-keeping obligations in ordinary maintenance practice.

Interaction with manufacturer information:

• The AD places reliance on Cessna Single Engine Service Bulletins SB04-25-01 Rev 4 (26 December 2006) and SB04-25-02 Rev 1 (17 October 2005) or Rev 2 (5 June 2006) as the prescriptive installation and fabrication instructions (Requirement 1). Operators must therefore obtain and follow those service bulletins. The AD’s safety requirement is implemented through these manufacturer documents, establishing an operational dependency on the manufacturer’s technical guidance.

Interaction with foreign regulator action:

• The AD references FAA AD 2007-05-10, which the AD notes in its “Note” as a source. That indicates alignment, or at least reference, to FAA’s corresponding directive. The AD does not reproduce FAA AD text but signposts it as a related authoritative source. Practitioners should note a lineage of technical directive between CASA’s AD and FAA action, although the AD does not state how conflicts or differences between the FAA AD and the CASA AD would be resolved.

What the AD does not specify about statutory interactions:

• The AD does not mention specific legislative provisions or sections of aviation statutes under which CASA issued the AD, nor does it set out administrative sanctioning powers. The AD therefore must be read together with the broader aviation statutory regime and CASA’s enforcement policy to understand legal consequences beyond the technical obligations it prescribes.

Operational interaction:

• The AD’s “before further flight” requirement for corrective actions discovered by inspection creates an operational interdiction that interacts with an operator’s flight operations. The AD does not specify how flight schedules or commercial obligations should be adjusted; it simply mandates that the action be completed “before further flight”, thereby necessitating operational adjustments when defects are found (Requirement 2(iii)).

In short, the AD operates as a technical regulatory overlay that references manufacturer and international regulatory materials for detailed method, imposes documentary obligations on operators (log book entry), and potentially constrains flight operations through “before further flight” requirements. The AD text does not set out statutory enforcement mechanisms or detailed cross-references to primary aviation legislation; those interactions must be inferred from the AD’s origin in CASA and read alongside the wider regulatory framework.

The supplied AD text includes identifiers and dates that establish its immediate provenance but contains no entries for subsequent amendments or revocations. The AD is identified as "AD/CESSNA 170/79", with the shorthand "5/2007 DM" visible in the header, and the document is dated 9 March 2007 with an effective date of 11 April 2007 (header; signature block; Compliance). The body references specific revisions and dates of manufacturer service bulletins (SB04-25-01 Revision 4, dated 26 December 2006; SB04-25-02 Revision 1 dated 17 October 2005, or Revision 2 dated 5 June 2006), which the AD uses as the operative technical documents (Requirement 1).

There is no text in the supplied document indicating that the AD has been amended, superseded or rescinded. The AD’s “Note” refers to FAA AD 2007-05-10 and the Cessna Service Bulletins as related documents, but the AD does not record any earlier or later Australian AD numbers or amendment entries. The multiple header repetitions (AD/CESSNA 170/79 appears several times in different formats) appear to be typographical or formatting duplication rather than evidence of an amendment history.

For practitioners seeking an authoritative amendment history, the supplied AD should be treated as the 2007 promulgation effective 11 April 2007. Any subsequent amendments, extensions, supersessions, or removals are not recorded in the supplied text; to establish whether the AD has been amended or remains in force, a practitioner would need to check the official CASA database or consolidated AD list outside of the supplied AD content. The AD itself provides the specific serial number applicability ranges and compliance provisions only for the 2007 directive as shown.

The AD does specify the precise versions of the Cessna service bulletins to be followed for compliance, and those service bulletin revision dates are part of the AD’s operative technical requirements. Those service bulletin revision references effectively lock the required compliance method to particular manufacturer-document revisions unless and until CASA issues an amendment that changes the referenced documents or acceptance criteria (Requirement; Note).

In summary, the supplied instrument records a single AD issued in March 2007 and effective 11 April 2007. The document contains no internal record of subsequent amendment or revocation; any change in status after that date is not reflected in the text provided.

The supplied AD contains no litigation history. There are no references to court challenges, judicial reviews, administrative appeals, or any disputes recorded within the instrument itself. The text is a directive specifying technical requirements, compliance timelines, and the associated service bulletin references; it does not recount any contested proceedings or give examples of enforcement litigation.

Because the AD does not provide any litigation or appeal information, practitioners who need to advise on potential contestation or judicial review would need to seek records outside the supplied AD , for example, CASA enforcement records, tribunal or court databases, or public registers that record challenges to regulatory action. None of those materials are present in the AD text provided.

The lack of litigation history in the AD does not preclude the existence of disputes in other records or subsequent legal actions; it only reflects that the AD itself contains no litigation narrative, outcomes, or case citations. For the purpose of legal due diligence, an advisor should treat the AD as a primary regulatory requirement and check contemporaneous and later regulatory and judicial sources to determine whether any party successfully challenged, sought variation of, or obtained relief from the obligations set out in the AD.

In short, the AD as supplied includes no litigation history; it contains purely technical and compliance content, with no references to court or tribunal proceedings.

Narrow applicability and serial-number reliance

• The AD’s Applicability lists narrow serial number blocks for the Cessna 172R and 172S (17280001-17281262; 172S8001-172S9994). Practitioners should not rely on the AD’s header (which names multiple Cessna series) alone; the formal Applicability field controls scope. An aircraft owner who assumes coverage because of model name alone risks unnecessary work or missing the AD if their serial number falls outside the listed blocks (Applicability).

Two distinct compliance pathways with different urgency

• The AD creates two different treatment tracks depending on whether Modification Kit MK172-25-10A or MK172-25-10B is already installed. Aircraft without A/B installed face phased compliance windows tied to TIS (0-500 hours: 12 months; 501-1,000 hours: 8 months; >1,000 hours: 4 months), whereas aircraft with A/B installed must undergo an installation inspection within 30 days and rectify any discrepancies before further flight (Requirement 1; Requirement 2; Compliance). Misclassifying an aircraft’s modification status can lead to missed deadlines or inappropriate intervals.

Time-in-service (TIS) as the compliance trigger

• The compliance windows for aircraft without A/B are measured from the AD’s effective date and depend on the aircraft’s TIS on that effective date (Compliance). Operators must have accurate TIS records as at 11 April 2007 to determine the applicable compliance deadline. Incomplete or inaccurate TIS records can cause mis-timing of compliance actions.

Specificity about service bulletin versions

• The AD mandates particular revisions and dates of Cessna service bulletins (SB04-25-01 Rev 4 dated 26 December 2006; SB04-25-02 Rev 1 dated 17 October 2005 or Rev 2 dated 5 June 2006) (Requirement 1). Using a different revision or an amended bulletin without confirming CASA acceptance risks non-compliance with the AD’s terms. Practitioners should ensure the maintenance provider follows the exact revisions referenced, unless a subsequent CASA amendment changes the reference.

Fabrication option has technical implications

• Where MK172-25-10A/B are not present, the AD allows either installation of MK172-25-10C or fabrication and installation of a steel lock rod/bar per SB04-25-02 (Requirement 1). The fabrication option imposes a technical requirement to follow the manufacturer’s fabrication procedure; operators relying on fabrication must ensure the maintenance organisation has the capability to fabricate to the service bulletin standards and document compliance accordingly.

Log book entry as primary documentary proof

• In the scenario where MK172-25-10A/B is installed and inspection finds no discrepancy, the AD requires a log book entry showing compliance (Requirement 2(ii)). That log book entry is the AD’s specified evidence. Failure to make an appropriate log book entry may render it difficult to demonstrate compliance, even if the inspection was performed.

“Before further flight” operational constraint

• If the inspection required for aircraft with kit A/B installed finds discrepancies, corrective actions must be taken “in accordance with” SB04-25-01 Revision 4, and the AD requires those corrective actions be completed before further flight after the inspection (Requirement 2(iii); Compliance). That can result in immediate operational grounding until remedial work is finished.

Cross-references to FAA AD and Cessna service bulletins

• The AD’s Note references FAA AD 2007-05-10 and the Cessna service bulletins. Practitioners should avoid assuming that FAA materials supersede CASA’s AD; rather, CASA’s AD mandates compliance per the cited documents. The AD does not specify procedures for resolving differences between FAA guidance and CASA’s directive.

No explicit penalties or enforcement language

• The AD does not specify penalties or enforcement mechanisms (Penalties and enforcement). Operators may be tempted to assume the absence of penalty language reduces urgency; however, the AD nonetheless imposes mandatory technical obligations with specific timelines and “before further flight” constraints. Operators should not treat the absence of explicit penalty clauses as an absence of regulatory force.

Duplication and formatting anomalies

• The supplied document contains repeated header lines and duplication (several instances of AD/CESSNA 170/79 and the title). While this appears to be a formatting artifact, practitioners should rely on the substantive Applicability, Requirement, and Compliance fields for legal effect rather than on the surrounding typographical layout.

Record retention and audit readiness

• The AD requires a log book entry in one scenario but does not elaborate on longer-term record retention or reporting to CASA. Operators should be prepared to retain records of installations, fabrications, inspections and corrective actions, including the service bulletin references and revision numbers used, to demonstrate compliance if required.

In sum, the principal “gotchas” are the narrow serial-number applicability, the bifurcated compliance pathways, the TIS-dependent deadlines, the requirement to follow specific service bulletin revisions, the need for accurate log book entries, and the potential for immediate operational grounding where discrepancies are found.

Step 1 , Confirm applicability

• Check the aircraft serial number against the AD’s Applicability: Cessna 172R serial numbers 17280001 through 17281262 and Cessna 172S serial numbers 172S8001 through 172S9994 (Applicability). Only aircraft with serial numbers within those blocks are targeted by this AD. Document that check (serial number, aircraft log reference).

Step 2 , Determine current modification state

• Inspect maintenance records and the airframe to determine whether Modification Kit MK172-25-10A or MK172-25-10B is installed. The AD’s required action depends on whether A/B are present (Requirement 1; Requirement 2).

Step 3A , If neither MK172-25-10A nor MK172-25-10B is installed

• For each crew seat (pilot and co-pilot), either:
  • Install Modification Kit MK172-25-10C following Cessna Single Engine Service Bulletin SB04-25-01 Revision 4 dated 26 December 2006, or
  • Fabricate and install a steel lock rod/bar following Cessna Single Engine Service Bulletin SB04-25-02 Revision 1 (17 October 2005) or Revision 2 (5 June 2006) (Requirement 1).
• Choose installation or fabrication based on cost, availability of the kit, and maintenance capability. If fabricating, ensure the maintenance organisation strictly follows the SB04-25-02 procedure and documents materials and dimensions used, aligning with the service bulletin’s acceptance criteria.

Step 3B , If MK172-25-10A or MK172-25-10B is installed

• Perform an installation inspection for each crew seat in accordance with Cessna Single Engine Service Bulletin SB04-25-01 Revision 4 dated 26 December 2006 (Requirement 2(i)).
• If no discrepancies are found, make a log book entry showing compliance with the AD. The AD specifies that such an entry is the required documentary evidence and no further action is necessary (Requirement 2(ii)).
• If discrepancies are found, perform all corrective actions required by SB04-25-01 Revision 4, and complete those corrective actions before further flight after the inspection (Requirement 2(iii); Compliance).

Step 4 , Observe the compliance windows and operational constraints

• For aircraft without MK172-25-10A/B installed, determine the appropriate compliance deadline using the aircraft’s time-in-service as at the AD’s effective date (11 April 2007): over 1,000 hours , within 4 months; 501-1,000 hours , within 8 months; 0-500 hours , within 12 months (Compliance).
• For aircraft with MK172-25-10A/B installed, perform the inspection within 30 days after the AD effective date, and complete corrective action before further flight if discrepancies are found (Requirement 2(i); Compliance).

Step 5 , Use the exact service bulletin revisions cited

• Obtain and keep copies of the precise Cessna Single Engine Service Bulletins referenced in the AD:
  • SB04-25-01 Revision 4, dated 26 December 2006 , associated with MK172-25-10C installation and the installation inspection and corrective action procedures for aircraft with MK172-25-10A/B installed.
  • SB04-25-02 Revision 1 (17 October 2005) or Revision 2 (5 June 2006) , associated with fabrication and installation of a steel lock rod/bar.
• Ensure the maintenance organisation follows the procedures and acceptance criteria in those revisions. Document the revision and date of each bulletin used in the maintenance records and log book entry.

Step 6 , Document work and retain records

• Make the log book entry required by the AD where applicable (Requirement 2(ii)). For installations, fabrications, inspections and corrective actions, record:
  • The work performed (installation of MK172-25-10C or fabrication details and drawings used);
  • The service bulletin reference and revision date used to perform the work;
  • The date of completion and the name/registration of the certifying maintenance organisation or engineer;
  • Any parts used and their provenance.
• Retain these records for audit and compliance demonstrations. Although the AD requires only a log book entry in one scenario, comprehensive records provide evidence of compliance across all scenarios.

Step 7 , Operational safety checks

• After installation or corrective action, perform any functional checks or test flights required by the service bulletin to confirm the seat back cylinder lock assembly performs to the acceptance criteria in the service bulletin. Document these checks in the maintenance record.

Step 8 , Liaise with regulator or manufacturer if uncertain

• If there is uncertainty about whether a particular kit is installed, whether the fabrication method complies with the service bulletin, or whether a different service bulletin revision should be used, consult the Cessna service bulletins cited or contact CASA or Cessna for clarification. The AD itself references FAA AD 2007-05-10 and the service bulletins as the technical sources (Note); use the explicit references in the AD as the starting point for clarification.

Step 9 , Operational planning for “before further flight” work

• For inspections that reveal discrepancies (particularly where A/B are installed), plan for the aircraft being grounded until corrective action is completed, since the AD requires corrective action to be completed before further flight (Requirement 2(iii)). Anticipate potential maintenance slots, parts procurement and authorisation requirements.

Step 10 , Maintain audit trail for future changes

• Keep a complete audit trail (work orders, parts invoices, sign-off documentation, service bulletin copies, photographs) in case future regulatory or purchaser due diligence requires proof of compliance with this AD. Although the AD’s text requires only a log book entry in one scenario, prudent operators should maintain a fuller set of records for installations and fabrications to demonstrate adherence to the specific service bulletin procedures and acceptance criteria cited in the AD.

By following those steps and adhering explicitly to the service bulletin revisions cited in the AD, operators and maintenance organisations will implement the technical changes the AD mandates. The AD’s effective date (11 April 2007) is the reference point for the timing obligations, so track deadlines against that date (Compliance).