The Federal Aviation Administration (FAA) has issued a critical airworthiness directive (AD) requiring immediate inspections of over 2,600 Boeing 737 aircraft. This directive affects the Boeing 737-700, 737-800, and 737-900ER from the Next Generation (NG) family, as well as the 737 MAX 8, 737 MAX 8-200, and MAX 9 models. The directive comes in response to concerns over the reliability of the oxygen mask systems in these aircraft.

Oxygen Mask Systems at Risk

The FAA’s decision follows numerous reports indicating that passenger supply unit (PSU) oxygen generators have been shifting out of position within their assemblies due to a failure in the retention mechanism. Boeing’s investigation pinpointed the issue to the pressure-sensitive adhesive (PSA) material used in certain generator strap thermal pads. These thermal pads are crucial in securing the oxygen generators within the PSU assembly.

“This condition, if not addressed, could result in shifted PSU oxygen generators that might become nonfunctional, which could result in an inability to provide supplemental oxygen to passengers during a depressurization event. The FAA is issuing this AD to address the unsafe condition on these products.”

Historical Context and Urgency

Depressurization events, while rare, can be catastrophic if the oxygen supply systems fail. One notable incident underscoring the importance of reliable oxygen systems occurred on Alaska Airlines flight AS1282. During this flight, a mid-air door plug blowout caused cabin depressurization, triggering the deployment of oxygen masks. Such incidents highlight the critical nature of functional oxygen systems during emergencies.

The FAA, recognizing the urgency of the situation, opted to bypass the usual notice and comment period typically required for such directives. The directive was filed on July 8 and published on July 10, with an effective date set for 15 days post-publication. This expedited process reflects the FAA’s assessment that the risk to public safety justified immediate action.

Scope and Compliance

The directive impacts 2,612 Boeing 737 aircraft within the United States. Data from ch-aviation indicates that this includes 2,095 active 737-700, 737-800, 737-900, 737 MAX 8, 737 MAX 8-200, and 737 MAX 9 aircraft, alongside stored or undelivered units.

Boeing has issued Special Attention Requirements Bulletins (RB) 737-35-1210 and 737-35-1211 for the affected 737 MAX and 737 NG families, respectively. These bulletins mandate a general visual inspection (GVI) of the PSU oxygen generator installations to determine the thermal pad configuration of the retention straps. Operators are required to conduct these inspections to identify any issues with installation migration or expended oxygen.

Inspection and Mitigation Actions of the Oxygen Mask Systems

The FAA outlined specific actions for operators to ensure compliance:

1. General Visual Inspection: Operators must inspect the PSU oxygen generator installations to determine the configuration of the thermal pads.
2. On-Condition Actions: If any issues are identified, operators must perform further GVIs to detect installation migration and any expended oxygen. Necessary repairs include repositioning affected PSU oxygen generators and replacing PSA retention strap thermal pads with non-PSA pads.

The cost implications of these inspections and repairs vary. The FAA estimated that the initial inspection to determine thermal pad configuration would cost operators $85 per aircraft, totaling approximately $222,020 for all affected U.S.-based aircraft. However, the costs for on-condition actions are variable and depend on the extent of the issues identified. These costs include:

• Inspection for Expended Oxygen and Installation Migration: $85 per aircraft.
• Replacement of PSU Oxygen Generator: Up to $1,459 per aircraft.
• Replacement of PSA Retention Strap Thermal Pads: $153 per pad.
• Repositioning of PSU Oxygen Generators: $85 per aircraft.

The FAA’s directive underscores the importance of rigorous maintenance and inspection protocols to ensure passenger safety. By addressing the potential failure of PSU oxygen generators, the FAA aims to mitigate the risks associated with cabin depressurization events.

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