U.S. NTSB warns of smoke risk in 737 MAX cockpit after engine safety system activates
NTSB warns of CFM LEAP-1B engine flaw that can flood cockpit with smoke, issues urgent recommendations to FAA, Boeing, and CFM
The U.S. National Transportation Safety Board (NTSB) has issued an urgent safety bulletin (AIR-25-03) outlining the risk of a Boeing 737 MAX cockpit filling with smoke following the activation of a safety device in its CFM International LEAP-1B engines. The agency has issued five new safety recommendations, including one urgent measure directed at the Federal Aviation Administration (FAA), to mitigate the risk.
The NTSB launched its investigation after an incident on December 20, 2023, involving Southwest Airlines Flight 554, a Boeing 737-8 that ingested a bird into its left engine shortly after takeoff from New Orleans. Moments after the impact, the flight deck filled with a “white, acrid smoke,” severely limiting the pilots' visibility.
The first officer reported he could no longer see the captain clearly, while the captain noted his instrument panel was hard to read, even considering flying the aircraft solely via the Head-Up Display (HUD). The smoke only began to clear rapidly after the crew activated the engine fire switch, as outlined in the emergency checklist.
What is the safety flaw in the 737 MAX engines?
A component called the Load Reduction Device (LRD), designed to protect the engine during fan blade failures, can cause an oil leak when activated. This oil burns in the engine’s hot sections, and the resulting smoke is introduced into the cockpit through the air conditioning system.
A failure with unexpected consequences
The root of the issue lies in a design feature of the engine known as the Load Reduction Device (LRD). This system protects the aircraft and engine from severe vibrations caused by fan blade imbalance or failure, by partially disconnecting the fan from the turbomachinery.
According to the NTSB, the LRD activation in the New Orleans incident caused engine oil lines to detach, allowing oil to enter the compressor. When exposed to high temperatures, the oil produced smoke that was sucked into the air conditioning system—which draws air directly from the left engine and supplies it to the cockpit.
A similar incident occurred on March 5, 2023, in Havana, Cuba, where Southwest Flight 3923 suffered a bird strike in the right engine, resulting in “vapor” entering the passenger cabin.
While current emergency procedures, such as activating the engine fire switch, close the Pressure Regulating and Shutoff Valve (PRSOV) to stop contaminated air, the NTSB stressed the need to reduce smoke levels and pilot workload during such emergencies.
CFM International and Boeing are currently developing a software update that will automatically close the PRSOV when the LRD is activated. However, this solution is not expected to be certified and available until Q1 2026.
Given this timeline, the NTSB issued the following key recommendations:
- To the FAA (Urgent): Ensure all 737 MAX flight crews are informed about this risk and that flight manuals (FCOM) and quick reference handbooks (QRH) reflect the updated procedures. The NTSB found that some pilots were unaware of the incidents.
- To Boeing and CFM: Collaborate to finalize and certify the software modification.
- To the FAA and EASA: Require all operators to install the software update once available.
- To the FAA, EASA, and CAAC: Assess whether LEAP-1A engines (used on Airbus A320neo) and LEAP-1C engines (on COMAC C919), which also use LRDs, present similar risks and take necessary corrective action.
The NTSB concluded that while the reviewed events involved bird strikes, LRD activation can occur due to other causes, such as the loss of a fan blade. Therefore, it is critical that flight crews are prepared for this contingency until a permanent fix is implemented.
AUTOR
Desde 2017, haciendo periodismo aeronáutico. Award-Winning Journalist: Ganador de la edición 2023 de "Periodismo de Altura", otorgado por ALTA. Facts don't care about your feelings.
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