The reporter has raised a safety concern to highlight a systemic hazard within the Part 121 operator’s Safety Management System (SMS) regarding the management of cabin air quality events (AQEs). The reporter states there have been multiple AQEs in recent months with a particular aircraft in the fleet, [Aircraft registration] an [Aircraft type 1].
The reporter advised, internal reporting mechanisms ([reporting system]) appear insufficient to guarantee a non-punitive analysis focused on system behaviour. Furthermore, the handling of these events demonstrates a culture where operational pressure (on-time performance) is prioritised over the safety of passengers and crew.
Reporting barrier
The reporter states, 'The operator has recently removed structured reporting tools available for cabin crew ([check list document])'. The reporter further advised, the cessation of the [check list document] has removed structured prompts that captured accurate and complete data concerning AQEs. This data was helpful to differentiate benign smells from safety-critical AQEs and assisted engineering to conduct a root cause analysis. Now, with the reduced data, the information is more ambiguous.
Procedural drift
The reporter states, '[procedure manual] contains a design flaw by defining the known contamination signature (the dirty socks smell) as not noxious and one that does not result in harmful physical symptoms. Comparisons between [date] and [date] [procedure manual] editions suggest a shift toward more ambiguous definitions, increasing the threshold required for cabin crew to suspect, and a pilot to declare a 'fume event'. This amendment actively degrades the safety margin. The manual creates a distinction between 'smell' and 'fume' that is scientifically unsound and may mislead crew'. The reporter provided the following information taken from the [procedure manual];
The definition: The [procedure manual] defines a 'smell' (specifically citing 'dirty socks' odour) as 'an unidentified, localised odour'. A smell is not noxious and does not result in harmful physical symptoms, for example, 'dirty socks’ smell'.
The risks: By officially defining this specific odour as 'not noxious', the operator mandates that crew ignore a warning sign of a bleed air defect.
The [procedure manual] also highlights the drift from previously requiring all cabin crew to report if present during an AQE. This is no longer a requirement or recommendation for cabin crew, only the Cabin Supervisor and Captain who may not have even been in the affected cabin area.
Unmanaged chronic defect
The reporter advised, an internal investigation failed to account for the aircraft technical history ([aircraft registration]), including two auxiliary power unit (APU) replacements in early 2024 due to fume contamination and five AQE events in [month] 2025. This demonstrates systemic issues to manage recurrent defects.
Just Culture
The reporter provided an example of a post AQE event interaction that demonstrated a breakdown of Just Culture where the focus shifted to minimising operational impact and assigning blame. Questions were directed at cabin crew such as, 'So who is the "sick" crew member?' assigning blame, and phrases such as, 'All of this to stay at [overnight accommodation]' show an assumption of malingering. This creates a punitive environment that discourages the reporting of physiological symptoms or safety concerns.
Requested safety actions
The reporter advised, the sole purpose of this report is to initiate systemic safety improvements and ensure passengers and crew are protected from potential exposure and managerial or operational pressure by highlighting the mishandling of AQEs. Further, the reporter requests the operator implement the following safety actions;
1. Procedural correction: The operator must rescind and revise the [procedure manual] definition for 'smell.' Known hazard signatures (for example characteristics of oil odours) must be classified as potential safety defects requiring investigation, not dismissed as benign.
2. Mandatory sampling: Implement a requirement for independent air quality sampling / swabbing following any AQE report that includes objective physical signs.
3. Reinstate reporting structure: Reintroduce a mandatory, structured AQE reporting tool for cabin crew to capture timing, location, and symptom data.
4. Additional just culture training: Training for flight crew and maintenance focused on non-punitive responses to frontline safety reports.
5. Acknowledgement: The operator should transparently acknowledge the discrepancies between their internal definitions ([procedure manual]) and industry standards regarding bleed air hazards.
The reporter finally states, the concern is how potentially serious air quality hazards are dismissed with minimal investigation, due to system-wide knowledge gaps, reporting barriers, and operational pressures. Additionally, this report is submitted for the purpose of enhancing transport safety and identifying systemic failures to protect crew and the public.
Thank you for the opportunity to respond to the concerns raised under REPCON RA2025-00189. We take these matters seriously as safety is our highest priority, and we appreciate the intent of the report to enhance systemic safety outcomes.
Commitment to Safety
Air Quality Events (AQEs) are a key focus for our business. To ensure robust management and continuous improvement, we have established a [working group] – a cross-functional team dedicated to reviewing AQE processes, implementing enhancements, and driving improved safety outcomes across operations.
Response to Specific Concerns
1. Removal of cabin crew [check list document]
The [check list document] was never used for engineering troubleshooting purposes. Engineering investigations rely solely on the flight crew forms [maintenance document 1] ([aircraft type 2]) and [maintenance document 2] ([aircraft type 1]), which capture the required technical information. For this reason, the [working group] determined that [checklist document] did not provide any additional value to support troubleshooting and therefore removed it. Our current reporting processes remain robust and compliant with SMS requirements.
2. [Procedure manual] definitions
The [procedure manual] definitions reflect industry guidance and manufacturer documentation to assist crew in differentiating between benign odours and potential AQEs. The cited 'dirty socks' smell is widely recognised as non-noxious. Our procedures remain aligned with safety standards and do not degrade safety margins.
3. Technical history and chronic defect management
Contrary to the claim that technical history was overlooked, our records show that [aircraft registration] was managed under chronic defect tracking [defect number] from the first AQE in [date]. All subsequent maintenance actions were linked and reviewed in accordance with [maintenance manual for proactive / predictive maintenance]. Additionally:
- There is no evidence of two APU replacements in early 2024 on [aircraft registration]. The only related action was an APU lube module replacement following an AQE.
- APU replacements due to AQEs are tracked across the fleet, and [aircraft registration] had one replacement in 2025.
This demonstrates compliance with approved procedures and proactive management of recurrent defects.
4. Just Culture
We acknowledge the importance of fostering a supportive reporting environment and can confirm that Just Culture principles are deeply embedded in our operations. All teams, including senior leaders and broader leadership groups, undertake Just Culture training supported by the [partner airline], ensuring alignment with the [partner airline]'s policy and procedures.
A review of all AQE events confirms that crew involved have been supported by their leadership teams in accordance with our SMS. We have found no evidence of punitive behaviour; rather, our approach is consistently supportive and people-first, encouraging open reporting and prioritising the wellbeing of our people.
Summary
The concerns raised do not reflect our current practices. Our AQE management processes are robust, supported by a dedicated working group, and aligned with industry standards. We remain committed to maintaining the highest levels of safety for passengers and crew.
Thank you for the opportunity to review the REPCON. CASA considers the matters contained within the REPCON to be a valid concern that may impact safety and acknowledge the operator's immediate actions. CASA has completed a desktop review and has not identified any non-compliances at this time. CASA will include the information provided within the REPCON in its oversight approach for the identified operator.