AD/B737/346 Amdt 1 — Cabin Altitude Warning Takeoff Briefing

An airworthiness directive (AD) is a legally enforceable notification issued by CASA (or delegated authority) requiring corrective action on an aircraft, engine, propeller, or appliance to ensure continued safe operation. This AD, numbered B737/346 Amdt 1, is one such instrument. It addresses the cabin altitude warning system. In many Boeing 737 models, the cabin altitude warning and the takeoff configuration warning share a single intermittent warning horn. The difficulty for flightcrews is distinguishing whether the horn indicates a depressurisation event (requiring immediate oxygen use) or a takeoff configuration error (which can be addressed differently). The AD’s solution is a takeoff briefing that requires the flightcrew to mentally prepare for that ambiguity and rehearse the memory items before every flight. The Aircraft Flight Manual is the primary operating document approved by the regulator for each aircraft type; altering it is a formal process. The AD requires Limitations and Normal Procedures sections to be revised. The Limitations section of an AFM contains mandatory operating limits and operating rules that the flightcrew cannot deviate from. The Normal Procedures section contains the step by step procedures for normal operation. The briefing requirement is inserted into both sections, making it both a limitation and a normal procedure. A memory item is an action that must be performed from memory without reference to a checklist during the immediate response phase of an emergency. The AD specifies three memory items: donning masks, setting 100% oxygen, and establishing crew communications. The fourth step (doing the checklist) comes after those immediate actions. The phrase intermittent warning horn is critical: the cabin altitude warning is intermittent (sounding in pulses) compared to a steady tone for the takeoff configuration warning, though that distinction may not be obvious in a high workload situation. The Alternate Means of Compliance (AMOC) concept allows an operator to use a different method than prescribed in the AD, provided an equivalent level of safety is demonstrated. Here, Amendment 1 adds the FAA approved AMOC 130S-09-134a as an acceptable alternative for requirement 2 only (the Normal Procedures briefing text). The hypoxia risk is the underlying safety hazard: insufficient oxygen in the body leads to progressive incapacitation, impairment of judgement, and eventual unconsciousness. The background section states that flightcrew have been failing to recognise and react to the cabin altitude warning, increasing the risk of incapacitation and loss of control. The directive is a procedural intervention that does not require the installation of the warning lights that would make the horn’s purpose unmistakable. That is a lower cost regulatory choice but places the compliance burden on human behaviour rather than engineering.

The primary persons affected are operators of any of the fourteen listed Boeing 737 models: 100, 200, 200C, 300, 400, 500, 600, 700, 700C, 800, 900, and 900ER series. This covers the entire classic and next generation 737 family up to the 900ER. Australian operators of these aircraft, whether airlines, cargo operators, charter companies, or corporate flight departments, are bound. The directive specifically mentions the pilot in command as the person responsible for ensuring the briefing is conducted. The flightcrew (both pilots) must receive the briefing, perform the memory items if the horn sounds, and both must verify the cabin altitude is below 10,000 feet before removing masks. Maintenance and continuing airworthiness management organisations may need to update the AFM revision documentation, track compliance dates, and ensure that the AD is incorporated into the operator’s approved maintenance program or in the continuing airworthiness management exposition (CAME). Because the AD allows the revision to be performed by inserting a copy of the directive, the compliance can be a simple administrative task, but it still requires coordination between maintenance and flight operations departments. CASA delegates such as Peter Nikolic, who signed the instrument, are involved in issuing and amending such directives. The FAA indirectly affects compliance because the AD references FAA AD 2008-23-07 and allows an FAA approved AMOC. Operators that hold both Australian and US airworthiness approvals must ensure compliance with both regimes. The suppliers of AFM revisions (e.g., Boeing or third party vendors) may be involved in preparing a formal revision that includes the required text, though the AD permits a simple insert for immediate compliance. Training organisations and check pilots may need to incorporate the cabin altitude warning briefing into initial and recurrent simulator training to ensure flightcrews are familiar with the memory items. Passengers are not directly affected by this AD, but the safety benefit is to reduce the risk of hypoxia related crew incapacitation, which could lead to loss of control and affect everyone on board. The shareholders and insurers of operators are indirectly affected because non compliance can lead to grounding, enforcement fines, and increased liability risk. The AD imposes a recurring operational cost: every first flight of the day and every time flightcrew change, the briefing must include this additional item. While the briefing repetition is low marginal cost, it extends the takeoff briefing, potentially by one to two minutes. For high volume operators, this accumulates into thousands of crew hours annually. The burden disproportionately falls on airlines operating older 737 models that lack the separate warning lights; newer models may have the lights installed and activated, and therefore may not fall within the scope of the AD at all. Operators must determine whether their specific aircraft have those lights and whether they are activated; if not, the AD applies.

The instrument imposes specific duties on operators and pilots in command, and grants limited rights of alternative compliance. The first duty is to revise the Limitations section of the AFM to include the prescribed statement about cabin altitude warning takeoff briefing. This revision must be completed within 120 days of 30 September 2013 (the effective date of Amendment 1; compliance periods run from the amendment effective date, not from the original 2008 date, because the AD as amended restates the requirements). However, operators who already complied with the original 2008 AD by inserting the text then are already compliant; Amendment 1 does not require a fresh revision for requirement 1. The second duty is to revise the Normal Procedures section to include the briefing text exactly as quoted in requirement 2. The duty to revise extends to each applicable AFM copy. An alternative duty applies to operators who obtain and use the FAA approved AMOC 130S-09-134a, which satisfies requirement 2. That AMOC letter presumably allows a different location, wording, or method of presenting the briefing, but the exact alternative text is not provided in the AD. Operators must ensure the AMOC is current and properly incorporated. The duty to brief is an ongoing operational duty. Before engine start for the first flight of the day, and before engine start after any change of either flightcrew member (e.g., a crew swap on a multi sector day, or a new first officer joining for a rotation), the pilot in command must ensure that the cabin altitude warning indications and procedures have been briefed. The directive does not prescribe who delivers the briefing, only that the pilot in command ensures it is briefed. The briefing content is specified: memory items for the intermittent warning horn sound in flight (immediate oxygen donning, 100% regulator, crew comms, then the checklist) and the verification step before removing oxygen masks. The right to alternate means of compliance is a significant entitlement. It allows operators to avoid the administrative burden of revising the Normal Procedures section if they have FAA approval and CASA, by this AD, accepts that approval as meeting requirement 2. Operators can also choose to remove the AD insert once the AFM is formally revised (by a normal or temporary revision) to incorporate the same information. The operator has the right to treat the AD insert as a temporary revision that can later be removed, avoiding permanent alteration to the AFM. The AD places no explicit duty on CASA beyond issuing the directive; the delegate exercises the right to sign under delegated authority. Flightcrew have the right to expect that the briefing has been conducted and that the AFM revision is current, which is essential for safety but not a legal right enforceable against the operator beyond contractual duties. The instrument does not grant any right of appeal; operators dissatisfied with the AD would have to challenge it under administrative law principles, not under the AD itself.

The text of AD/B737/346 Amdt 1 does not specify penalties. Enforcement arises from the underlying framework of the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations 1998 (CASR). Operating an aircraft that does not comply with an applicable airworthiness directive is a serious breach of the conditions of the aircraft’s certificate of airworthiness. Under CASR Part 42 (continuing airworthiness), the registered operator or the owner is responsible for ensuring compliance with all applicable ADs. Failure to comply makes the aircraft unairworthy. The Civil Aviation Act provides for civil penalties of up to 1,000 penalty units for individuals (currently 1 penalty unit = A$313 as of 2025, so A$313,000) and higher for bodies corporate. Criminal liability may arise under section 20A of the Act for reckless operation endangering safety, but that would be reserved for egregious cases beyond mere non compliance. More commonly, CASA can issue an Enforceable Voluntary Undertaking (EVU), a suspension or revocation of the air operator’s certificate (AOC), or a direction to ground the aircraft until compliance is achieved. Practical enforcement typically begins with an audit finding that the AFM revision or briefing is missing. CASA’s Continuing Airworthiness Management Organisations (CAMOs) are required to verify AD compliance as part of their annual airworthiness review. Non compliance may be detected during ramp inspections or flight operations audits. For the briefing duty, proving non compliance requires evidence that the briefing did not occur on a given flight, which is difficult unless an inspector observes the briefing or the aircraft’s flight data recorder or voice recorder reveals the omission. The more easily verified obligation is the AFM revision itself: the AFM is a static document that can be inspected. The 120 day compliance period means that operators who fail to update the AFM by late January 2014 (if the amendment effective date is used) are in breach. The amendment does not extend the compliance date from the original AD; rather, it adds an alternative means of compliance. Operators who complied with the original 2008 AD are already compliant; those who did not are already in breach and the Amendment does not waive that breach. The delegation of enforcement powers to CASA delegates (such as the signatory, Peter Nikolic) is standard. Enforcement actions are discretionary, but CASA has a stated policy of seeking voluntary compliance before escalating. The risk of enforcement imposes a compliance cost on operators: they must document the AFM revision, train crews, and maintain records to prove compliance in case of audit. The economic consequences of non compliance include direct financial penalties, legal costs, reputational damage, and the business interruption cost if the aircraft is grounded.

The AD operates within a hierarchy of Australian aviation safety legislation. It is issued under powers delegated by the Civil Aviation Safety Regulations 1998 (CASR) , which were made under the Civil Aviation Act 1988. CASR Part 39 specifically governs airworthiness directives, setting out the process for issuing, amending, and complying with them. AD/B737/346 Amdt 1 is a legislative instrument and is registered on the Federal Register of Legislation (FRL). It references FAA AD 2008-23-07 Amdt 39-15728 as a related instrument. This creates a cross border interaction: the Australian AD mirrors the FAA AD but with a later amendment date (2008 FAA, 2013 Australian amendment). Operators of US registered aircraft operating in Australia must comply both with the FAA AD and the Australian AD; if conflicts exist, the more restrictive requirement applies. The existence of an FAA approved Alternate Means of Compliance letter 130S-09-134a shows bilateral recognition of safety approvals between CASA and the FAA, likely under the Bilateral Aviation Safety Agreement (BASA) and associated Implementation Procedures for Airworthiness. The AD also ties into Part 42 of CASR, which requires operators to have a continuing airworthiness management system that tracks AD compliance. Under Part 42, operators must maintain a register of each AD and its application status. The AD’s requirement to revise the AFM interacts with CASR Part 61 (flight crew licensing) and Part 91 (general operating and flight rules). Part 61 requires pilots to be familiar with the AFM; the AD effectively changes the procedures they must be familiar with. The briefing duty interacts with Civil Aviation Order 82.5 or equivalent regulations that prescribe the content of takeoff briefings; this AD adds a mandatory item to that regulatory requirement. The directive is also subject to the Legislation Act 2003, which governs the making, registration, and commencement of legislative instruments. The AD is signed by a delegate of CASA; the validity of the delegation must be in accordance with the Acts Interpretation Act 1901 and the Civil Aviation Act 1988, section 98 (delegation of powers). If the AD were to conflict with any other Australian law (e.g., workplace health and safety laws that might impose conflicting duties), the aviation specific legislation would prevail to the extent of the inconsistency, but a court would attempt to reconcile them. The Competition and Consumer Act 2010 (including the Australian Consumer Law) is not directly engaged, though a failure to comply with an AD could be used as evidence of a safety defect in a product liability claim under the ACL. The instrument does not mention any privacy or data protection laws, as it deals only with flight procedures.

The source instrument is Amendment 1 to AD/B737/346, meaning at least one earlier version existed. The background section states that the original issue of this AD became effective on 25 November 2008. That original directive presumably required the same AFM revisions without the alternative means of compliance. Amendment 1 is dated 10 September 2013 and becomes effective on 30 September 2013. The sole substantive change introduced by Amendment 1 is the addition of an alternate means of compliance: “Amendment 1 allows the revising of the AFM as per the approved FAA AMOC Letter 130S-09-134a dated 28 April 2009 as an alternate means of complying with requirement 2 of this AD.” Requirement 2 is the Normal Procedures section revision. The Limitations revision (requirement 1) is not affected by the amendment. The text of the Normal Procedures revision itself is unchanged. No other amendments are referenced. The AD was originally issued in response to FAA action on recurring reports of flightcrew failing to recognise the cabin altitude warning. The 2008 original was likely identical in substance. The 2013 amendment thus provides additional flexibility: operators who had already secured an FAA AMOC could rely on that instead of inserting the exact prescribed text into the Normal Procedures section. This may reduce compliance cost for operators that already held that AMOC. The amendment was signed by Peter Nikolic, Delegate of CASA, on 10 September 2013, and appeared in the Gazette or FRL as AD/B737/346 Amdt 1 with the number 20/2013. The instrument does not state whether the original 2008 AD was published under a different number or if it was also CASA or automatically adopted from the FAA. The Australian AD system generally tracks FAA AD numbers, but CASA may reissue them under a local numbering scheme. The note referencing FAA AD 2008-23-07 Amdt 39-15728 indicates the FAA counterpart. There is no indication of any further amendments after 2013 as of the source document. The AD remains current until superseded or withdrawn. No sunset date is provided. Operators should verify whether CASA has issued any subsequent amendments or cancellations since 2013, but they are not part of the source. Amendment history shows a regulatory responsiveness to operator feedback: allowing AMOC increases operational flexibility and reduces the burden of mandatory wording when an equivalent method already exists. This is a modest but welcome concession to practical compliance.

The source instrument does not refer to any litigation. No cases are cited within the text. It is unknown whether any operator has challenged the validity of AD/B737/346 in the Administrative Appeals Tribunal or the Federal Court. However, the general aviation regulatory context in Australia shows that airworthiness directives are rarely litigated directly. Operators typically comply or seek an AMOC rather than challenge the instrument. The power to issue ADs under CASR Part 39 is broad, and courts give significant deference to CASA’s safety assessments. A challenge would need to demonstrate that the AD is unreasonable, ultra vires, or procedurally defective. Grounds could include a failure to consult (though the legislation does not require consultation for individual ADs), unreasonable burden, or that the AD is not supported by evidence. Given the background (FAA reports of flightcrew failing to react), a challenge would be difficult. The use of a delegate rather than the CASA Board personally is standard and has not been successfully challenged in analogous cases. The AD amends an existing AD, which may imply that the original was accepted without litigation. The addition of an AMOC via Amendment 1 may have been influenced by operator representations, avoiding the need for adversarial proceedings. Operators who disagree with a particular AD usually engage in informal discussions or submit an AMOC request rather than go to court, because litigation is costly and time consuming and the aircraft must be grounded in the interim if the AD requires immediate action. The only potential litigation would be in the context of an enforcement action: if CASA issues a fine or suspends an AOC for non compliance, the operator may seek judicial review of the enforcement decision, and the validity of the AD could be raised as a defence. There are no reported Australian cases involving this specific AD. The United States may have some litigation related to the underlying FAA AD or from incidents involving hypoxia, but those are outside the Australian legal system and are not referenced. The instrument is stable and uncontested in Australia to date. Legal practitioners advising operators should note the absence of litigation as evidence that compliance is relatively straightforward, but operators should still ensure they are compliant to avoid becoming the first test case.

Several traps within the AD could catch operators off guard. First, the scope depends on whether the CABIN ALTITUDE and TAKEOFF CONFIG lights are installed and activated. The AD applies only to aeroplanes in which those lights are not installed, or are installed but not activated. Operators must determine the exact configuration of each aircraft in their fleet. A common misbelief might be that because a 737 has those lights, the AD does not apply. But the AD also applies if the lights are installed but not activated. If the lights are installed but inoperative or deactivated, the AD applies. Operators should verify the activation status in the aircraft’s original certification and any modifications. Second, the compliance deadline from Amendment 1 is 120 days after 30 September 2013 for both requirements. Operators who did not comply within that period remain in breach. There is no grace period. The original 2008 AD had its own compliance date; Amendment 1 does not restart that clock. Operators who were compliant with the original AD remain compliant; those who were not are still non compliant and will not be rescued by the amendment. Third, the note about FAA AD 2008-23-07 suggests that operators of US registered 737s must ensure compliance with both ADs. The Australian AD does not automatically incorporate the FAA AD; it is a separate obligation. Compliance with one does not guarantee compliance with the other, though the content is likely identical. Fourth, the AMOC only applies to requirement 2. Requirement 1 (Limitations revision) must still be complied with as written. Operators who use the FAA AMOC must still insert the Limitations text verbatim. Fifth, the briefing must occur before engine start. Some operators may overlook the “before engine start” timing and try to conduct it after start, e.g., during taxi. The AD is explicit: it is a takeoff briefing to be completed before engine start for the first flight of the day or following crew change. That imposes a pre flight discipline. Sixth, the briefing requirement triggers on any change of either flightcrew member, not just the pilot in command. A change of first officer on a multi sector day necessitates a fresh briefing. This could multiply the briefing frequency for long haul operations with multiple crew changes. Seventh, the memory items are mandatory and must be briefed. However, the AD text in the Normal Procedures section says they “must be briefed” but does not explicitly state that the memory items must be performed if the horn sounds in flight. That is implied by the checklist. The briefing must include those items, but failure to perform them in flight could be a separate operational violation. Eighth, the AFM revision may be accomplished by inserting a copy of this Directive. That seems simple, but if the directive has multiple pages, care must be taken to place the correct pages in the Limitations and Normal Procedures sections. The AD does not specify which pages go where. Operators should create an AD compliance sheet that clearly shows the inserted text and its location. Ninth, the removal of the AD insert is permitted only when the information is inserted into the AFM by a normal or temporary revision. Many operators might never incorporate it formally and continue to rely on the insert; that is acceptable as long as the insert remains legible and properly located. But if the insert is lost or removed, the operator would be non compliant. Tenth, the instrument is a legislative instrument that creates legal obligations, but it is easily overlooked because it appears only on the FRL and not in the operators’ main compliance databases. Operators must have systems to track amendments to ADs, not just the original issue. Amendment 1 changed compliance options without reprinting the entire AD. A failure to note the amendment could lead an operator to continue using an outdated compliance method that is no longer valid or to miss the AMOC flexibility.

Compliance with AD/B737/346 Amdt 1 requires a methodical approach covering documentation, crew training, and ongoing operations. Step one: determine which aircraft are affected. Review the Boeing 737 models listed; any aeroplane in the Australian register that matches one of those fourteen variants must be evaluated. For each aircraft, check whether the CABIN ALTITUDE and TAKEOFF CONFIG lights are installed and activated. If they are not installed, or are installed but not activated, the AD applies. This may involve consulting the aircraft’s type certificate data sheet, maintenance records, or the flight deck configuration listing. If the lights are installed and activated, the AD does not apply and no action is needed for that aircraft. Step two: revise the AFM Limitations section. Insert the exact text as stated in requirement 1: “CABIN ALTITUDE WARNING TAKEOFF BRIEFING … as part of the Takeoff Briefing before engine start for the first flight of the day or following any change of either flightcrew member, the pilot in command will ensure the Cabin Altitude Warning indications and procedures are briefed in accordance with the procedures contained in the Normal Procedures section of this manual.” This can be done by including a copy of the AD page in the Limitations section marked as a temporary revision, or by issuing a formal revision (normal or temporary) that includes the text. Step three: revise the Normal Procedures section. Insert the briefing text from requirement 2, including the full paragraph and the bullet points. Alternatively, if the operator holds FAA AMOC 130S-09-134a (or obtains it), they may use that as an alternate means of compliance for requirement 2 only. The AMOC letter must be approved by FAA and accepted by CASA (the AD does this by reference). The operator should retain a copy of the AMOC in the AFM or in the aircraft records. Step four: ensure the briefing is conducted. This is an operational duty. The pilot in command must include the cabin altitude warning briefing in the takeoff briefing before engine start for the first flight of the day and after any change of flightcrew member. The briefing must cover: (a) immediate donning of oxygen masks setting 100% when the intermittent warning horn sounds in flight, (b) establishing crew communications, (c) performing the CABIN ALTITUDE WARNING OR RAPID DEPRESSURIZATION checklist, and (d) both pilots verifying on the overhead panel that cabin altitude is at or below 10,000 feet before removing masks. The operator should incorporate this requirement into standard operating procedures (SOPs) and into flight crew training curricula. Step five: document compliance. Maintain a record of the AFM revision (date, section, method) and a log of each briefing (either in the aircraft journey log or air safety report). While the AD does not explicitly require a written record of each briefing, the burden of proof in an enforcement action would rest on the operator. Practical compliance includes an SOP checklist item for the briefing. Step six: track fleet wide implementation. For a fleet of multiple 737s, ensure each aircraft’s AFM is revised. Coordinate with the continuing airworthiness management organisation. If new aircraft are added to the fleet, determine compliance status at acquisition. Step seven: review for future amendments. Check periodically (at least annually) whether CASA has amended or superseded this AD. The instrument as provided is Amendment 1; there may be later amendments not in the source. Subscribe to the Federal Register of Legislation or CASA’s AD alerts. Step eight: consider training and simulation. While not mandated, operators should include the cabin altitude warning scenario in recurrent simulator training to ensure flightcrew can execute the memory items effectively. This reduces the risk of failure to respond, which is the underlying safety issue the AD addresses. The compliance burden is primarily administrative and training time; no hardware modifications are required. For most operators, the cost will be low, but the administrative cost of updating multiple AFMs for a large fleet can be significant if done manually.