After two serious 737 Max engine outages caused by birds, Boeing alerts pilots

SEATTLE — Last year, two Southwest Airlines 737 Max jets lost engines on takeoff after striking large birds, emergencies made much more serious when smoke and fumes penetrated inside the airplanes.

Flight crews on both aircraft — one taking off from Havana, the other from New Orleans — followed procedures and made emergency landings back at the airports.

Recognizing an abnormally high risk in these two unusual incidents, Boeing sent an alert to airlines in February to make sure pilots know the correct procedure in such an emergency to quickly stop the penetration of smoke and fumes.

In response, United conducted “a thorough review of training and existing procedural guidance for our pilots.” Southwest and American — the other U.S. airlines operating the Max — sent notices to their pilots detailing what had happened and explicitly flagging the right procedure to use.

The goal was to minimize the risk of catastrophe in the future if pilots facing a similar incident didn’t handle it as well as the two Southwest crews did. Yet a detail in Boeing’s alert — mention of a system on the Max’s LEAP engine the pilots hadn’t known about — caused concern among some pilots.

That system, a fail-safe feature developed by engine maker CFM International, worked as designed to constrain even worse damage to and a potential breakup of the engine.

But pilots want to know more about the system, which is not in their manuals, and how exactly it performed in these two incidents.

Southwest’s notice said it intends to update its flight manual for the Max with information about the system. But that hasn’t been issued yet.

“We haven’t been told a lot,” said Tom Nekouei, vice president of the Southwest Airlines Pilots Union, or SWAPA. “We’re still kind of in limbo.”

Two emergencies

On March 5, 2023, as Southwest Flight 3923 took off from Havana, Cuba, headed for Fort Lauderdale, Florida, the right engine — which feeds air to the passenger cabin — collided with multiple birds and was severely damaged. The plane was a new 737 Max 8, just over three months old.

When smoke began to pour into the cabin, the crew dropped the oxygen masks above each passenger seat. Chaos erupted as the passenger cabin filled with thick smoke.

The pilots turned the plane around and landed. As soon as they taxied off the runway, all passengers evacuated via emergency slides as airport firefighters doused the engine with water.

There were no reports of serious injuries and the passengers later flew to Fort Lauderdale on a different plane.

On Dec. 20, as Southwest Flight 554 climbed out of New Orleans, headed for Tampa, Florida, the left engine — which feeds air to the flight deck — smashed into a large bird.

Again the aircraft was a Max 8, this time almost a year old, with 168 people on board.

Soon after takeoff, the pilot declared an emergency and told the tower he needed to return to the airport. In the audio of the radio transmissions, someone, perhaps a pilot in a plane behind, can be heard saying, “You guys have smoke coming out of one of your engines.”

Southwest confirms smoke entered the cockpit as the plane wheeled around. In the pilot’s conversation with the air traffic control tower, his voice was distorted and muffled as he spoke through an oxygen mask.

When the tower asked if emergency vehicles should be deployed around the runway, the pilot replied, “We need everything you have.”

Invited by the controller to land, the pilot replied that he was “running some checklists” and needed a few more minutes. Busily checking out everything, when asked a second time, again the pilot replied that, “We aren’t quite ready.”

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SWAPA vice president Nekouei described smoke in the cockpit as “one of the top five bad emergencies you can have in an airline.”

The two pilots are “wearing smoke goggles and talking to one another through those Darth Vader masks, trying to work through the checklist,” he said.

The Flight 554 crew did so and finally were ready. They made their approach and landed the plane safely.

New Orleans airport firefighters checked out the engine from the outside and saw no fire. The aircraft taxied to a gate for normal deplaning.

The right procedure to save the plane?

It’s not uncommon for a bird strike to take out an aircraft engine. It is unusual to get smoke inside the plane as a result.

The cause is described in Boeing’s service bulletin and in the Southwest and American notices to the pilots, which were reviewed by The Seattle Times.

In both cases, the bird strikes caused “damage to the engine oil sump.” Leaking oil then entered the hot core of the engine and burned.

On modern airliners, the air from inside the jet engines is cooled, then fed into the plane’s interior to regulate the temperature and air flow. Air from the left engine flows into the flight deck, from the right engine into the passenger cabin.

In both Southwest incidents, smoke was funneled straight into the airplane’s interior.

With an engine destroyed and smoke inside the airplane, three different checklists in the pilot manual might seem applicable.

There’s one checklist detailing what a pilot must follow when an engine fails, and another for finding the source of smoke inside the airplane and eliminating it.

The first stops the engine but keeps the air flowing. The second methodically checks a number of potential electrical system sources.

Neither would immediately stop the smoke pouring in and in these circumstances a swift response is required.

“Having a bird strike that causes an engine to fail close to the ground is challenging enough, but throwing in smoke and additional checklists is a human factors stress point,” said Dennis Tajer, a captain with American Airlines and spokesperson for the that airline’s pilot union, the Allied Pilots Association.

The only pilot choice in this situation that will stop the smoke intrusion is a checklist used when an engine is on fire or severely damaged.

In that procedure, the pilot shuts down the engine and pulls a fire handle. This second step cuts the flow of air from the engine, closing off the source of the smoke.

Boeing’s bulletin clarified exactly what the pilots must do: “The presence of smoke in the flight deck or cabin associated with an engine failure should be considered engine severe damage.”

“We did provide extra guidance in a bulletin to ensure crews know to prioritize,” Boeing spokesperson Bobbie Egan said.

“Pilots are trained to respond to specific events or conditions. In this case, the conditions are an engine failure, fire and smoke, all of which are clearly evident to a pilot,” said Egan. “Even though this should be clear from their training, we chose to emphasize it.”

An engine system that’s news to the pilots

The pilot manual and training lay out the conditions that tell a pilot when to use the procedure for engine fire or severe damage. One of those is heavy vibrations accompanied by abnormal engine warnings on the instrument panel.

This is where a new system on the Max’s engine is relevant. It’s called a load reduction device, or LRD.

The major change to the 737 design with the Max was a new engine called the LEAP, made by CFM International, a 50-50 joint venture between GE and French company Safran and the exclusive engine provider for the 737 since the 1980s.

The LEAP is also the most popular of two engine choices on the rival Airbus A320 jet family.

Replacing the earlier engine that powers the prior 737 NG model, the LEAP has a much bigger fan to add fuel efficiency. CFM added the LRD technology as another upgrade and it’s on both the Airbus and Boeing versions of the LEAP.

If an engine fan is badly damaged in flight, say by a bird strike, broken fan blades will throw the rotating parts off balance.

That will cause the whole intricate mechanism to shake and heavy vibrations can lead to further damage.

When this happens, the new LRD safety feature activates and disconnects the fan blades from the rotor turning the fan. The fan blades then spin freely.

CFM said this allows the fan to decelerate rapidly “to minimize disturbance to the rest of the engine and its connections to the aircraft.”

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Since airline mechanics must maintain the Max engines on a daily basis, the LRD is duly described in the airline maintenance manuals.

An entry in the maintenance manual describes the LRD’s purpose — “to protect the aircraft in case of heavy vibration” — and how it works.

But airline pilots were not similarly informed.

Boeing in a statement explained that the LRD does “not affect airplane handling, the crew cannot affect their operation, and no crew procedures change as a result of LRD activation.”

That’s the rationale for not putting the LRD in the Max pilot manual. It activates automatically when severe damage occurs. It doesn’t affect what the pilots do and they have no control over it.

Federal Aviation Administration spokesperson Jillian Angeline said “the pilot training for engine failures has not changed and does not specifically address the Load Reduction Device mechanism or functionality.”

Yet some pilots at Southwest and American were startled and unhappy to learn of this for the first time.

“If I have a system in the airplane that has a function, I need to know about it,” said SWAPA vice president Nekouei.

It’s also unclear why Boeing’s service bulletin and the airline notices to pilots mention the LRD. Since the crew cannot control it, what is its relevance to them? Did it have some role in these emergencies?

When the LRD works as it should to reduce vibration and further engine damage, could that mask the severity of the damage to the engine and lead pilots to use the wrong recovery checklist?

Boeing declined to comment. The FAA’s Angeline said there’s “no evidence” that the pilots in the Southwest incidents “were misled by engine symptoms in any way.”

A confidential hotline complaint — which The Seattle Times reviewed —submitted to the FAA under the whistleblower protection system by a Southwest pilot likens the withholding of information about the LRD to Boeing’s hiding of the Maneuvering Characteristics Augmentation System, or MCAS, that was a prime cause of the two fatal Max crashes five years ago.

Yet while MCAS was a badly flawed design, there’s no indication the LRD is defective.

The birds that struck the two Southwest engines “significantly exceed the size and weight” of those used in required certification tests, and yet “the engines performed as designed during these events,” said CFM spokesperson Nathan Hicks.

And although the LRD is new to the 737 on the Max model, CFM says the system is also on the 787 Dreamliner and 777 engines, both made by GE.

Still, American Airlines captain and APA spokesperson Tajer is unhappy.

“While this engine safety system appears to have a necessary function, we continue to seek information,” he said. “How does it impact the engine indications during an engine failure with severe damage? And why did the engine sump fail to contain its oil?”

“The FAA has not fully considered the weight of this compound emergency and its risk to safely recovering the airplane,” Tajer added.

Likewise, Southwest’s Nekouei is angry that after two serious incidents he doesn’t know more about the LRD system.

“They have never briefed us,” he said.

In a statement, Boeing said “we continue to work with CFM to learn more about this matter and we are keeping the FAA and our operators informed of any learnings.”

The FAA said it “will determine if action needs to be taken as its investigation proceeds.”