Following two recent in-flight incidents involving a sudden and uncontrolled rise in temperature in both the passenger cabin and flight deck, the Federal Aviation Administration (FAA) has decided to act by issuing a new Airworthiness Directive for the Boeing 737 MAX family. The regulator emphasized that the assessed risk requires immediate operational measures until a permanent technical solution is introduced.
According to a notice published in the Federal Register, the issue is linked to activation of the BAT BUS SECT 2 switch, which can disrupt the operation of the air conditioning system. In such a scenario, “uncontrollably high temperatures” may develop in the cabin and cockpit. The FAA warned that this could lead to injuries or even incapacitation among crew members and passengers, thereby jeopardizing flight and landing safety.
The directive applies to the 737-8, 737-9 and 737-8-200 (MAX) variants, covering a total of 2,119 aircraft worldwide, including 771 registered in the United States. Crews have reported situations in which existing procedures were insufficient to stabilize the aircraft’s internal temperature.
As an interim measure, the FAA requires amendments to flight manuals within 30 days. Operators must introduce additional emergency procedures, including a controlled descent to a lower altitude, an attempt to reset the affected switch and, if unsuccessful, shutting off engine bleed air. These steps provide crews with a clearer operational framework for managing the situation in flight.
The manufacturer, Boeing, supported the regulatory decision and confirmed it is working on a permanent engineering solution to eliminate the possibility of the electrical fault. The root cause has been identified as a grounding issue within the air conditioning system. The company expects the final modification to be implemented on the 737 MAX 7 and MAX 10 models before their certification, without affecting planned timelines.
One of the incidents involved an aircraft operated by Southwest Airlines, which confirmed it remains in close communication with both the regulator and the manufacturer and has further briefed its crews on handling this specific electrical malfunction.
The FAA stressed that the directive represents a temporary but necessary measure — a clear signal that even operational details within complex systems such as air conditioning are treated with the same level of regulatory scrutiny as all other safety-critical elements of an aircraft.
