NTSB Calls for LEAP-1B Fixes; Boeing Plans Update by 1Q26

The US National Transportation Safety Board (NTSB) has issued urgent safety recommendations concerning the CFM International LEAP-1B engines installed on Boeing 737 MAX aircraft, following incidents of smoke intrusion into aircraft cabins and cockpits. These recommendations are directed at the Federal Aviation Administration (FAA), Boeing, CFM International, and international regulators, aiming to mitigate risks associated with the engines' Load Reduction Device (LRD).

The NTSB investigation began after a Dec. 20, 2023, incident involving Southwest Airlines Flight 554, a Boeing 737-8 MAX departing from New Orleans. Shortly after takeoff, the aircraft ingested a bird into its left engine, a CFM LEAP-1B, causing "acrid white smoke" to fill the cockpit. According to the NTSB report, the smoke severely impaired pilot visibility. The first officer reported difficulty seeing the captain clearly, while the captain struggled to read the instrument panel and considered relying solely on the head-up display. The crew followed emergency procedures, including activating the engine fire switch, which eventually reduced the smoke and allowed the aircraft to land safely with no injuries.

The smoke intrusion was traced to the activation of the Load Reduction Device, a system designed to protect the engine from damage caused by fan blade failure or imbalance by partially disconnecting the fan from the turbomachinery to reduce vibration loads. The NTSB found that when the LRD activates, it can cause oil lines within the engine to separate, leaking oil into hot engine sections and generating smoke that the aircraft’s air conditioning system can draw into the cockpit or passenger cabin.

A similar event occurred in March 2023 on Southwest Airlines Flight 3923 departing Havana, Cuba, where bird ingestion led to vapor entering the passenger cabin from the right LEAP-1B engine.

The NTSB emphasized that while current emergency checklists instruct crews to activate the engine fire switch—which closes the pressure regulating shutoff valve (PRSOV) to block contaminated air— minimizing smoke ingress remains critical to reduce pilot workload and enhance safety during emergencies.

CFM International, a joint venture between GE Aerospace and Safran Aircraft Engines, and Boeing are developing a software update intended to automatically close the PRSOV upon LRD activation. This modification aims to limit smoke entry more effectively and reduce crew workload. However, certification and availability of this software are not expected until 1Q26.

Given the timeline, the NTSB issued several key recommendations:

• To the FAA (urgent): Ensure all 737 MAX operators inform flight crews about the smoke risk associated with LRD activation and update the Flight Crew Operations Manual (FCOM) and Quick Reference Handbook (QRH) accordingly. The NTSB noted that some pilots were unaware of these incidents and risks.

• To Boeing and CFM International: Complete development and certification of the software modification to address the issue.

• To the FAA and the European Union Aviation Safety Agency (EASA): Mandate installation of the software update by all operators once available.

• To the FAA, EASA, and the Civil Aviation Administration of China (CAAC): Assess whether similar risks exist for the LEAP-1A and LEAP-1C engine variants, used on Airbus A320neo and COMAC C919 aircraft respectively, which also employ LRDs, and take corrective measures as needed.