Internal Debate Over CFM Leap Safety System Prompts FAA Review

The FAA plans to review the risks of a common but rarely needed engine safety system that prompted a rare set of urgent internal recommendations calling for new procedures and design changes for the Boeing 737 MAX family

At issue is the CFM Leap load reduction device (LRD)—a purpose-built weak link that separates the fan rotor from its surrounding supports when a fan blade breaks or the fan suffers major damage, such as from a large-bird strike. On the Leap 1B-powered 737 MAX family, in certain scenarios LRD activation causes oil to be ingested into the environmental conditioning system (ECS), which delivers air directly from the left (No. 1) engine to the cockpit and from the right (No. 2) engine to the cabin.

The FAA’s office of accident investigation (AVP) is concerned that both scenarios create unacceptable risk and should be addressed with short- and long-term steps. AVP officials took the unusual step of issuing recommendations to its own agency.

In an Oct. 28 memo to FAA’s Safety Recommendations Branch, which normally manages correspondence from the NTSB and similar external sources, AVP made six “emergency” recommendations.

Key among them is to adopt new temporary pilot procedures that prohibit using the No. 1 engine ECS pack until the aircraft is above 3,000 ft. The FAA accident investigation experts also want Boeing and CFM to redesign the system, so the affected ESC pack is deactivated or bleed pressure regulating shut-off valve (PRSOV) is closed as soon as an LRD-triggering event is detected. The current LRD logic closes the affected PRSOV, but not immediately.

The No. 2 engine ECS pack can feed both the cockpit and cabin during departures, the AVP memo said.

Another alternative, considered “the most conservative approach” in the memo, is to keep both packs off and use the auxiliary power unit (APU) for bleed air.

AVP also pointed out its “very concerning” discovery that 737 MAX flight or training manuals do not reference the LRD or potential hazards of an activation.

AVP’s findings stem from examining two Southwest Airlines 737-8 bird-strike incidents with similar results: one fractured fan blade and a subsequent LRD activation.

One, in March 2023, happened when a turkey vulture struck the No. 2 engine as the aircraft was departing Havana. The second occurred in December 2023, when a bald eagle flew into the aircraft’s No. 1 engine as it was departing New Orleans.

Cuban authorities opened a formal investigation into the March incident. NTSB has not announced a formal probe of the December occurrence.

In both incidents, the pilots followed appropriate procedures, a Southwest memo issued in February said. “They performed as trained, methodically maintained aircraft control, donned oxygen masks when necessary, and executed” the appropriate non-normal checklists (NNCs), the Southwest memo added.

The Southwest bulletin emphasized that an engine failure accompanied by smoke in the cockpit or cabin should prompt pilots to follow the “Engine Fire or Severe Damage or Separation” NNC first, followed by two smoke, fire and fumes NNCs.

American Airlines, which also operates 737-8s, provided a similar bulletin to its pilots. “An engine failure on takeoff followed by the presence of smoke or fumes must be dealt with promptly, but in a methodical manner,” the American bulletin said. “Maintaining aircraft control while donning oxygen masks is essential while executing the Engine Fire or Engine Severe Damage or Separation NNC. Once [that NNC] is complete, the Smoke, Fire or Fumes NNC and the Smoke or Fumes Removal NNC should be completed as required.”

Both airline memos were based in part on an Operations Manual Bulletin issued by Boeing in February that highlighted the existing NNCs. AVP’s memo spotlighted the issue and seemingly helped spur wider agency action.

“The FAA is addressing the CFM Leap 1B engine issue through our standard continued operational safety process, which includes close collaboration with Boeing, CFM and the European Union Aviation Safety Agency (EASA),” the agency said late Nov. 21. “We will convene a Corrective Action Review Board (CARB) in the coming weeks to examine the data and develop a path forward. The FAA determined this is not an immediate flight-safety issue.”

While the FAA statement does not mention AVP’s memo, the recommendations, which apparently were not coordinated with others in the agency, will surely be discussed. Airline sources familiar with the debate said a key unknown about the AVP’s solution is the risk of adding a required task—toggling ECS packs on—below the critical flight phase threshold of 10,000 ft.

It is unclear what, if any, changes will result from the FAA CARB.

Boeing said it is “working with the authorities that are investigating these incidents.” CFM said it is “collaborating with FAA, EASA and Boeing to determine if there are any learnings from recent events.” Sources with knowledge of each manufacturer’s thinking said no design or procedural changes are in the works based on findings to date.

Neither Boeing nor CFM would comment on potential LRD system changes.

LRD devices are not new. In addition to engines made by CFM International, a 50-50 joint venture of GE Aerospace and Safran, GE-family engines with the devices include the GE90, GEnx, CF34-10 and GE9x, as well as the GP7200 made by GE and Pratt & Whitney. In nearly 275 million flight hours, GE-family engines have seen four reported LRD activations, data shared with Aviation Week shows. In each case, the aircraft landed safely.

While the AVP memo focuses on the 737 MAX incidents, it references Leap 1A-powered Airbus A320neo-family aircraft as posing a similar risk.

One provider of 737 pilot guidance has developed new procedures based in part on the AVP recommendations. Subscribers of the 737 Cockpit Companion (CC) book and app, which include pilots at airlines of all sizes, will soon see an LRD overview and new NNC for scenarios involving systems activations, CC co-founder and former 737 pilot Bill Bulfer told Aviation Week.

The CC approach is to use the APU for bleed air when departing in a suspected large-bird environment. “That really should be the first choice,” Bulfer said. “It’s easy to do and it’s approved.”

Its new checklist, “Engine Failure During Takeoff—Bird Environment,” calls for the non-flying pilot to immediately turn off the affected bleed switch. It also calls for immediate donning of oxygen masks at the first sign of cockpit air contamination.

Bulfer does not often add bespoke checklists to his CC content, but the LRD issue is unusual. “This one just struck me right away,” Bulfer said. “I told [co-founder Robert Dorsett], ‘This has to go out to the pilots, because this can happen anytime.’”