The US Department of Transportation’s (DOT) top inspector is reviewing a controversial Federal Aviation Administration decision related to an engine issue that can cause thick smoke to quickly inundate Boeing 737 Max cockpits and cabins.
Additionally, Boeing is now developing a software fix to address the concern, which involves a “Load Reduction Device” in the 737 Max’s CFM International Leap-1B turbofans.
At least one airline is also now warning pilots that a similar issue can affect Airbus A320neo-family jets powered by CFM Leap-1As.
“Our objective is to assess FAA’s actions in response to recent incidents of toxic smoke and fumes entering aircrafts’ cockpit or cabin when Load Reduction Devices are activated,” says a 16 April memorandum from Nelda Smith, assistant inspector general for aviation audits in the DOT’s Office of Inspector General. “We plan to conduct our audit at FAA’s offices involved in the decision-making process for the LRD issue.”
The FAA in November 2024 decided against taking immediate steps to address the LRD risk, despite an FAA accident investigation panel recommending immediate action.
“We welcome outside scrutiny and will fully cooperate with the audit,” says the FAA of the DOT’s review.
Neither Boeing nor CFM, a GE Aerospace-Safran Aircraft Engines joint company, immediately responded to requests for comment.
The Leap turbofan’s LRD is a safety device intended to prevent more-extensive damage when an engine loses a blade or suffers severe blade damage. When activated, the system decouples the fan rotor from fan supports, preventing an unbalanced fan from passing extreme loads to other components, according to a February 2024 CFM document viewed by FlightGlobal.
But when activated, the LRD also “opens” an oil sump, allowing oil to flow into hot engine sections and generating intense smoke.
Because the 737 Max’s left-side Leap supplies bleed air to the cockpit, a left engine LRD failure will cause that engine to pipe smoke into the cockpit. A right-engine LRD failure will cause the cabin to fill with smoke, as that turbofan supplies cabin air, documents show.
Two inflight incidents, both involving Southwest Airlines 737 Max 8s, highlighted the problem.
On 5 March 2023, a Southwest 737 Max 8’s right-side Leap struck a 1.8kg (4lb) turkey vulture shortly after take off from Havana, activating the engine’s LRD and causing “thick acrid smoke” to fill the cabin, according to an October 2024 report written by officials within the FAA’s Office of Accident Investigation & Prevention.
Then on 20 December 2023, the left engine of another Southwest 737 Max 8 ingested a 2.3kg bald eagle. That engine’s LRD activated, sending 14 litres (3.7USgal) of oil into its low-pressure compressor booster. “A toxic amount of smoke and fumes” was pumped into the cockpit, according to FAA and CFM documents.
The pilots of both jets landed safely.
The FAA’s October 2024 report said smoke from a left-side LRD activation can cause cockpit visibility to reduce to 5in in 30sec.
In November last year, CFM said of the issue, “Load Reduction Devices have been widely used across the industry for more than 20 years and operated as designed. We are collaborating with FAA, EASA and Boeing to determine if there are any learnings from recent events”.
RECOMMENDED ACTIONS
The FAA’s Office of Accident Investigation & Prevention thought the 737 Max’s LRD issue warranted immediate action.
Its October 2024 report made “emergency recommendations” to the manager of the FAA’s Safety Recommendations Branch. It urged the FAA to require that pilots follow modified take-off procedures, including taking off with at least the 737 Max’s left-engine bleed air system disabled.
The FAA followed up in November by convening a “Corrective Action Review board”, but that board declined to require revised take-off procedures. “The issue does not warrant immediate action”, the FAA said at the time, adding that it would address the concern through its typical rulemaking process.
The agency also issued a document called a “Continued Airworthiness Notification to the International Community”. That document noted that Boeing had provided operators with “enhanced instructions that direct flight crews more quickly to the appropriate actions when they experience abnormal engine indications”, the FAA now says.
Boeing, meanwhile, is developing a permanent solution, according to a March bulletin from American Airlines to pilots.
“Boeing is developing an Electronic Engine Control software update that will automatically close the bleed air valve if the Load Reduction Device is activated,” the memo says. “This software is undergoing testing and certification and is expected to be available in 2026.”
The LRD issue has raised concern among pilot groups including the Allied Pilots Association, which represents pilots at American Airlines.
LRD activations are likely to occur close to the ground, where bird strikes typically occur, and can leave pilots with near-zero visibility within seconds, APA says.
The union is “challenged to understand” why the FAA did not require revised take-off procedures or additional training prior to the permanent fix.
In February, American and Southwest Airlines issued pilot memos addressing the LRD-smoke issue. The memos told pilots to consider such an event an instance of “severe engine damage”, meaning they should respond by completing three checklists, including one that calls for shutting down the engine.
The Air Line Pilots Association, International, which represents United Airlines’ pilots, and the Southwest Airlines Pilots Association did not immediately respond to requests for comment.
On 4 April, American Airlines issued a pilot memo noting that LRD activation on A320neos with Leap-1As can also cause “a smoke/fume event in the cabin”.
That memo reminds pilots to address the issue by discharging the engine fire extinguishing bottle, which will close the bleed air and pack-flow control valves.
