The National Transportation Safety Board ( NTSB ) has revealed that CFM International, working with Boeing, will update the software of the 737 MAX engine, the LEAP-1B, following two bird strike events that have resulted in a lot of smoke ending up in the cockpit.
Cockpit filled with acrid white smoke
In a preliminary report issued by the NTSB, the investigators detailed one of the two bird strike events. On December 20, 2023, a Southwest Airlines flight from Louis Armstrong New Orleans International Airport (MSY) suffered a bird strike shortly after departure.
The airline's 737 MAX 8 , registered as N8830Q, was operating flight WN554 when at about 1,000 feet (304.8 meters), the left-hand engine suffered a bird strike that initially resulted in vibration and loss of thrust of the number one engine, a CFM International LEAP-1B.
Photo: Ian Dewar Photography | Shutterstock
According to the NTSB, shortly after the bird strike, the left engine master caution fire warning light and engine first switch illuminated, with the fire bell going off in the cockpit. In response, the captain, who was pilot flying (PF), called for the 'Engine Fire or Engine Severe Damage checklist' in the quick reference handbook (QRH).
As the first officer, acting as pilot monitoring (PM), began going through the checklist, the cockpit filled up with "acrid white smoke," according to the NTSB. In response, the PM called out "masks," and both pilots put on their masks, with the first officer resuming going through the QRH.
The pilots declared an emergency to Air Traffic Control (ATC) and asked for fire trucks to be present as soon as they returned to New Orleans. The captain told the investigators that visibility was limited and that he could see nothing beyond the first officer, adding that his instrument panel was difficult to see due to the smoke.
"The captain further stated that, after the engine fire switch had been pulled, the smoke began to rapidly dissipate."
Photo: Dorengo5 | Shutterstock
Eventually, the 737 MAX 8 landed back in New Orleans, stopping on the runway. After an inspection by the airport's rescue and firefighting (ARFF) services, the aircraft taxied to the gate, where the 139 occupants of the 737 MAX 8 successfully deplaned with no injuries.
The other bird strike event, which also resulted in smoke filling the cabin of the 737 MAX, happened in March in Cuba. The right-hand engine ingested the birds, forcing the aircraft to turn back to Havana.
The NTSB pointed out that while Southwest Airlines was not mandated to report either of the incidents, after the Federal Aviation Administration (FAA) began looking into the two bird strikes and the consequent severe smoke events, it started its own investigation into the two flights.
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Posts Engine oil entering the cabin's air supply
NTSB explained that the LEAP-1B engines are equipped with a load reduction device (LRD), which is designed to minimize aircraft and engine damage when there is a significant fan imbalance.
"The design was intended to enable the fan to be mechanically disconnected from the turbomachinery, thus reducing the severity of the vibration that is transmitted into the airframe."
The LRDs are a mechanical feature that does not require pilot input. When an LRD is activated, engine oil enters the compressor upstream of the pneumatic bleed ports, which supply bleed air to the cabin and flight deck, the NTSB said.
In a previous statement to Simple Flying, a CFM International spokesperson affirmed that LRDs have been widely used across the industry for more than 20 years and operated as designed.
"The LEAP engine meets FAA and EASA bird ingestion certification requirements. The birds in these incidents significantly exceeded the size and weight of regulatory bird ingestion certification standards; however, the engines still performed as designed during these events."
The preliminary report continued that engine bleed air from the high-pressure compressor (HPC) travels from the engine to the pressure regulating shutoff valve (PRSOV) and then to the left and right air conditioning packs. When closed, the valve prevents bleed air from the affected engine from entering the aircraft.
Photo: NTSB
"The valve closes automatically if the engine running relay is de-energized (the affected engine spools down below 62% minimum N2), the engine start switch is moved to cutoff, or the engine fire switch is pulled."
However, the investigators highlighted that the left air conditioning pack, supplied by the left engine, which suffered the bird strike in New Orleans in December 2023, supplies air to the cockpit. In turn, the right pack provides air to the cabin, while excess air from the left air conditioning pack is recirculated and combined in the mixing manifold and distributed to the cabin.
Photo: NTSB
In November, the FAA said that it would convene a Corrective Action Review Board (CARB) meeting to examine the flights' data and decide on a path forward. The regulator added that this was not an immediate flight-safety issue.
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The FAA will work with Boeing, CFM International, and EASA on further steps.
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On November 26, the FAA concluded that no immediate safety action was necessary to address the bird strikes and consequent smoke events. In a statement to Simple Flying, the regulator said:
"The CARB's work included evaluating several internal FAA safety recommendations. Based on the available data, the CARB determined the issue does not warrant immediate action and the FAA will follow its standard rulemaking process to address it."
Photo: Wirestock Creators | Shutterstock
The NTSB stated that after the bird strike event in New Orleans, Boeing released a Flight Crew Operations Manual (FCOM) bulletin and made updates to the FCOM and the QRH.,
"CFM International, in collaboration with Boeing, has begun work on a software design update."
Lastly, Southwest Airlines took action and, following the pair of bird strike incidents in 2023, incorporated Boeing's updated FCOM and QRH. The NTSB is continuing its investigation.
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The FAA was exploring whether to propose software changes that would change the way the LEAP-1B responded to a bird strike.
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