Boeing 737s to require passenger oxygen inspection | PaxEx.Aero

8 July 2024 By Seth Miller 1 Comment

Operators of Boeing 737 NG and 737 MAX aircraft face a new potential problem after “multiple reports of passenger service unit (PSU) oxygen generators shifting out of position within their associated PSU assemblies because of a retention failure.” Boeing issued Special Attention Requirements Bulletins to aircraft operators on 17 June 2024 alerting them to the problem.

The US Federal Aviation Administration followed this up with plans for an airworthiness directive (AD) mandating the inspection of all PSU oxygen generators and and replacement of offending installations on Monday morning. That rule is expected to be formally published in the Federal Register on Wednesday.

The directive describes the problem as coming from pressure-sensitive adhesive material on mounting pads holding the oxygen generators in place:

Boeing has investigated the condition and found that the oxygen generator retention failures were caused by a failure of the pressure-sensitive adhesive (PSA) material on certain generator strap thermal pads. The oxygen generator is secured to the PSU assembly by two retention straps, with either PSA or non-PSA thermal pads. For all reported failures, the PSA thermal pad configurations were under the retention straps. 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.

Because of the potential risk associated with not having oxygen available in the case of a depressurization event the FAA is skipping the comment period, typically made available when airworthiness directives are proposed. While not describing this as an emergency airworthiness directive (akin to the one which grounded many 737 MAX 9 aircraft after the exit door plug blowout in January), this one will see a significantly accelerated adoption and implementation timeline:

An unsafe condition exists that requires the immediate adoption of this AD without providing an opportunity for public comments prior to adoption. The FAA has found that the risk to the flying public justifies forgoing notice and comment prior to adoption of this rule because PSU oxygen generators might shift out of position within the PSU assembly because of a retention failure and become non-functional, which could result in an inability to provide supplemental oxygen to passengers during a depressurization event. Accordingly, notice and opportunity for prior public comment are impracticable and contrary to the public interest pursuant to 5 U.S.C. 553(b)(3)(B).

The compliance time in this AD is shorter than the time necessary for the public to comment and for publication of the final rule.

The AD impacts more than 2,600 planes registered to US airlines. Foreign authorities are likely to require similar inspections, meaning potentially every 737-700, 737-800, 737-900/ER, 737 MAX 8, 737 MAX 9, and 737 MAX 8200 could require inspection and mitigation of the issue.

The FAA’s estimate of cost impact suggests the initial inspection can be performed in one hour. This should allow airlines to inspect them all without facing significant operational disruptions. Performing the replacement of offending installations will take longer, however. And there is no way to determine how many will require the additional work prior to the initial inspection.

The full filing can be found here.

Update (10 July 2024):

The additional documentation is now public, with a requirement that all potentially affected planes be inspected within 120 days. If an aircraft is fount to have an oxygen container that is held by the offending straps or discharged as a result of slipping it must be resolved before that aircraft can resume service.

The DOT initially estimated the inspection would take one hour per aircraft. With 50+ PSUs to inspect that seems optimistic.

Did you enjoy the content? Or learn something useful? Or generally just think this is the type of story you'd like to see more of? Consider supporting the site through a donation (any amount helps). It helps keep me independent and avoiding the credit card schlock.

This story is about: 737, 737 MAX, 737 NG, Airworthiness Directive, Boeing, Department of Transportation, DoT, FAA, Federal Aviation Administration, regulations Filed Under: Airplanes and Airports