A small team of accident investigators within the Federal Aviation Administration have internally recommended a design change to fix an engine vulnerability on Boeing’s 737 MAX.

The same team also wants pilots to be fully informed of the risk and is asking for takeoff procedures to be modified until the design change is implemented.

An internal memo dated Oct. 28 from the FAA’s Office of Accident Investigation and Prevention outlines six recommendations to avert “the potential catastrophic risk” of smoke and noxious fumes spewing into the cockpit if a bird slams into the engine and activates a specific engine component.

The investigators recommend that FAA Administrator Mike Whitaker “require a design change which detects the immediate impulse of a bird-strike” or broken engine fan blade and automatically closes the affected engine’s airflow to the interior of the airplane “as quickly as possible.”

The memo does not represent a final FAA decision. The gravity of the risk and what should be done about it is still being discussed internally.

The safety regulator said Thursday that it will convene a Corrective Action Review Board in the coming weeks to examine the data and the investigators’ recommendations, and decide what action to take.

Ahead of that determination, the leaked FAA investigator recommendations have been circulating in aviation safety circles this week. They make clear the reason for a proposed change to takeoff procedures first reported Thursday by The Seattle Times.

The memo recommends that, until the permanent fix is available, all MAX pilots should be instructed via an emergency airworthiness directive to amend their takeoff procedures.

Two new pretakeoff options are offered. One would require the pilots to close off the airflow from the left engine, which goes directly into the cockpit.

Smoke from that engine could “quickly expose the flight deck to high concentrations of potentially lethal aerosolized chemicals at a critical phase of flight,” the memo states.

That smoke might incapacitate the pilots and cause the loss of the airplane as they struggle to handle the aircraft with one engine destroyed while close to the ground.

The second, more conservative option offered is to close off the airflow from both engines. The airflow from the right engine goes into the passenger cabin.

Dennis Tajer, spokesperson for the American Airlines pilot union, said he’d strongly favor this option. “We have to protect the passengers,” he said. “They shouldn’t be doused with lethal chemicals.”

Jeff Guzzetti, an aviation safety consultant and former FAA accident investigator who once ran the Office of Accident Investigation and Prevention, said the office that issued the memo consists of about eight people.

He said such safety recommendations typically go through a very deliberative review by different teams before a decision is made and the memo should not have been leaked before that.

“These two events certainly sound serious to me,” Guzzetti said. “However, there could be people inside the FAA — engine certification experts, engineers, test pilots — that would say this is not needed.”

“I just think this is part of the sausage-making of hard aviation safety decisions,” he added.

In contrast, American’s Tajer welcomes the leaking of the memo.

“Thank goodness they did this. That’s hero action,” Tajer said. “At least somebody gets that safety must be the No. 1 goal.”

It was American and Southwest pilots who were concerned about the two incidents that first drew public attention to this engine issue in June.

“We are relieved to see some of the things that we were concerned about being documented,” Tajer said. “Now we are going to demand to be a part of this process” to work with regulators and find the best safety solution.

Two serious emergencies in nine months

The recommendations in the memo are a detailed response to two serious emergency incidents on 737 MAXs flown by Southwest Airlines last year when each jet lost an engine on takeoff after colliding with a large bird.

Both emergencies became very serious when heavy smoke and fumes from burning engine oil flooded inside the airplanes.  

On a March 2023 flight taking off from Havana, smoke poured into the passenger cabin after a bird struck the right engine on takeoff.

In December, on a flight out of New Orleans, a large bald eagle estimated to weigh more than 12 pounds struck the left engine on takeoff and smoke filled the cockpit.

Bird strikes on engines are not uncommon; engines have to be tested and certified to withstand the impact of birds weighing up to 8 pounds.

Engines of older design more easily sustain serious damage. But strikes that destroy the robust carbon-composite fan blades on the more modern engines are very rare.

Still, the FAA memo states that Boeing needs “to reassess their projected probabilities” of such a destructive event, given that the Southwest incidents occurred just nine months apart.

A new safety feature on the engine

The internal FAA memo, reviewed by The Seattle Times, is highly critical of Boeing for not informing pilots about the existence of the engine component that activates when the engine is severely damaged, called the load reduction device, or LRD.

This device is new on the MAX’s LEAP engine, which is designed and built by CFM International, a joint venture of GE Aerospace and Safran of France. It was not part of the engine on the prior 737 model.

Ironically, the LRD is a safety feature designed to mitigate harm if an engine fan is badly damaged in flight, say by a bird strike.

A broken fan blade will throw the engine’s rotating parts off balance and cause heavy vibration throughout the intricate mechanism that can lead to further damage.

When this happens, the new LRD activates, shearing some bolts and disconnecting the fan from the engine core. The fan blades then spin freely and the vibration is minimized.

In the Southwest incidents, the violence of the engine fan breakup caused an oil leak from the engine sump. Ignited by the hot engine, the burning oil then sent smoke and fumes inside the airplane.

The memo cites a Boeing presentation stating that “the release of oil from the sump is an expected result of LRD activation.”

CFM says some version of an LRD has been widely used across the industry for more than 20 years and that it operated as designed in the two Southwest flight incidents.

Various models of the 777, 747 and 787 also have such an engine component. So does the larger version of LEAP engine on the Airbus A320neo jet family.

No similar incidents have been reported on the A320neo jets. Although their engines are similar in design, the way the airflow from the engines is controlled can be different.

A person familiar with the details of the engine system, who asked not to be identified because of the sensitivity of ongoing discussions between safety regulators, Boeing and engine maker CFM International, said a design change to address the smoke risk would not require any physical modification to the engine.

Instead, a software change would adjust the signal to the aircraft’s computers about what to do with the airflow valves when a fan blade breaks off, whether due to a bird strike or some other reason.

If such a software design change is settled upon, it must go through a stringent certification process that will include assessment of potential unintended consequences.

This summer, Airbus certified the latest version of its A320neo jet family, the A321XLR. Coming after the two Southwest incidents, the European regulator would have required Airbus to show that the same heavy bird strike scenario was not a substantial risk.

Boeing will have to do the same when the FAA certifies the two forthcoming MAX models, the MAX 7 and MAX 10.

And Boeing must once again consider how much information to share with pilots and airlines. There was nothing in the pilot manuals about the LRD.

The leaked FAA memo compares this to the similar omission from pilot manuals of any mention of the flight control system at the center of the two deadly MAX crashes, the Maneuvering Characteristics Augmentation System, or MCAS.

“Much like MCAS, the discovery that LRD is not known to pilots is very concerning,” the memo states.

The investigators recommend that the FAA “review all novel and unique 737 MAX design features and ensure they are adequately communicated in pilot operating manuals.”