NTSB: 737 MAX LEAP-1B Engine Fume Fix on Track for Q1 2026
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Boeing and CFM are finalizing a software fix for the 737 MAX LEAP-1B engine to prevent cockpit fumes, with a Q1 2026 target per an NTSB report.
Key Takeaways
- •Targets Q1 2026 for finalizing a LEAP-1B engine software modification.
- •Addresses a safety flaw that caused cockpit smoke during two 2023 bird strike incidents.
- •Responds to urgent NTSB Safety Recommendations A-25-13 and A-25-14.
- •FAA is expected to mandate the fix via a future Airworthiness Directive for all 737 MAX aircraft.
According to a National Transportation Safety Board (NTSB) report, Boeing and CFM International (CFM) are on track to finalize a software modification for the LEAP-1B engine by April 1, 2026. The update addresses a critical safety issue on the Boeing 737 MAX that could allow hazardous fumes to enter the cockpit following certain engine events. The fix, prompted by urgent NTSB safety recommendations, is expected to be mandated across the fleet by the Federal Aviation Administration (FAA).
The required modification stems from a design feature in the LEAP-1B engine, the exclusive powerplant for the 737 MAX family. The issue centers on the engine's Load Reduction Device (LRD), a system intended to reduce airframe vibrations if a fan blade is lost. However, investigations into two separate incidents revealed that an LRD activation could compromise engine seals, allowing oil and fumes to be drawn into the aircraft’s bleed air system, which supplies air to the cockpit and cabin. This represents a significant risk to flight crew situational awareness and safety.
Background on the Safety Incidents
The NTSB investigation was triggered by two events involving Southwest Airlines 737 MAX aircraft in March and December 2023. In both cases, bird strikes caused engine damage sufficient to trigger the LRD. The December 2023 incident was particularly severe; according to the NTSB's press release, the flight crew reported the cockpit filled with "acrid white smoke" so dense that the captain had difficulty viewing the instrument panel. This created a hazardous situation requiring the crew to don oxygen masks and execute an emergency diversion.
In response to these events, the NTSB issued Safety Recommendations A-25-13 and A-25-14 on June 18, 2025. These recommendations urged CFM and Boeing to complete the software modification and called for the FAA and its European counterpart, EASA, to mandate its installation. As an interim measure, Boeing issued a Flight Crew Operations Manual (FCOM) bulletin on February 9, 2024, to advise pilots of the potential hazard and outline appropriate procedures.
The Proposed Solution and Timeline
The planned fix is entirely software-based, reflecting an industry trend of using code to address mechanical or design vulnerabilities. The engine software design update is anticipated to be complete in the first quarter of 2026. Once finalized and certified, Boeing and CFM will distribute the update to operators via a service bulletin. Following its release, the FAA is expected to issue an Airworthiness Directive (AD), making the installation mandatory for all U.S.-registered 737 MAX aircraft and likely influencing similar mandates from other global regulators.
In a statement, Boeing confirmed its collaboration on the fix, saying: “CFM International and Boeing have been working on a software design update. We support the NTSB's recommendation.” However, pilot unions have expressed cautious optimism. The Allied Pilots Association (APA) stated: “We are pleased to hear that Boeing and CFM International are anticipating a fix to the LRD design flaw by the end of March 2026. We are concerned that just like the [Leap-1B] engine anti-ice design flaw fix, the LRD fix will take longer as well.” This comment highlights ongoing concerns about the timeliness of safety modifications for the aircraft.
Continued Scrutiny and Broader Context
This issue with the LEAP-1B's LRD system adds to a series of challenges that have kept the 737 MAX under heightened regulatory scrutiny. It is distinct from a previously identified concern with the LEAP-1B's engine anti-ice system, which could also lead to engine damage under specific icing conditions. Together, these issues underscore the complexities and potential for unintended consequences in modern, high-bypass turbofan engines.
The reliance on a software update also points to the increasing integration of digital controls in critical aircraft systems. While software can provide elegant solutions, it also introduces its own certification and validation challenges, which regulators are closely monitoring as part of a broader focus on aircraft certification processes.
Why This Matters
This engine fix is critical for ensuring the operational safety of the global Boeing 737 MAX fleet. The successful and timely implementation of the software modification will be a key step in addressing a documented vulnerability that poses a direct risk to flight crews. For airlines, the eventual Airworthiness Directive will necessitate another round of fleet-wide updates, impacting maintenance schedules and reinforcing the importance of robust safety management systems in monitoring in-service issues.
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Written by Ujjwal Sukhwani
Aviation News Editor & Industry Analyst delivering clear coverage for a worldwide audience. Covers flight operations, safety regulations, and market trends with expert analysis.
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