Regulators Confident Pilots Can Manage Engine Safety Device Risks

European and U.S. regulators have determined that risks introduced when a rarely needed Boeing 737 MAX safety device activates can be mitigated by pilots with existing procedures while the agencies deliberate whether longer-term changes are necessary.

The joint decision by the FAA and European Union Aviation Safety Agency (EASA) means pilots will follow new, Boeing-provided cues to the same checklist procedures as when an engine failure activates the load reduction device (LRD) that is integrated into the 737 MAX’s CFM International Leap 1B engines. The regulators’ conclusions, reached following a dedicated Corrective Action Review Board (CARB) held Nov. 26, overruled an internal FAA memo's  recommendations and disappointed some pilots.

Found on many engines, the LRD reduces dynamic loads transferred from a severely damaged fan to the attached structure, including the engine pylon. On the Leap family, fuse bolts fail, which disconnects the fan rotor from the engine core and allows the imbalanced fan to rotate separately.

The fan rotor’s unrestricted axial rotation brings fan blade tips into contact with surrounding components. While this helps slow fan rotation, it also opens an oil sump flange, releasing oil into the engine flow path. The flange opening is in front of bleed ports that feed pneumatic air cycle kits, or packs, responsible for regulating air temperature and pressure. On the 737 MAX, the No. 1 engine’s pack feeds the cockpit, while the No. 2 engine’s pack supplies cabin air.

An LRD activation will send smoke-filled air into a 737 MAX. When facing an “engine severe damage” scenario, pilots are instructed to follow a specific checklist that, among other things, closes the affected engine’s bleed pressure regulating shutoff valve (PRSOV) and stops the contaminated air from entering the cabin and cockpit. A damaged engine’s PRSOV also closes when the engine’s core slows to a certain rotational speed.

But recently released details on two incidents involving Southwest Airlines 737-8s suggest pilots have little margin for error to keep smoke from filling the cockpit or cabin following a substantial engine failure.

In the first incident, a turkey vulture struck the No. 2 engine as the aircraft was departing Havana en route to Fort Lauderdale, Florida, in March 2023. The second occurred in December 2023, when a bald eagle flew into the aircraft’s No. 1 engine as it was departing New Orleans for Tampa, Florida. In both cases, the pilots reacted promptly, managed the hazards and returned to their departure airports within about 10 min.

A Southwest memo issued in February lauded the pilots’ actions in each incident. “They performed as trained, methodically maintained aircraft control, donned oxygen masks when necessary and executed” the appropriate nonnormal checklists (NNC), the Southwest memo said. The 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. “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 on a Boeing Operations Manual Bulletin that highlighted the existing NNCs.

Experts in the FAA’s Office of Accident Investigation and Prevention (AVP) analyzed flight record data and other information from both incidents. Their conclusions, published in an Oct. 28 internal memo, differ sharply from those of Boeing and the airlines. The memo called for both immediate and long-term actions to minimize risks—principally smoke in the cockpit—that an LRD activation presents.

Key among the AVP’s six “emergency” recommendations is to adopt new temporary pilot procedures that prohibit using the No. 1 engine pack until the aircraft is above 3,000 ft. The AVP also wants Boeing and CFM to redesign the system so the affected pack is deactivated or its PRSOV closed as soon as an LRD-triggering event is detected. This, AVP reasoned, will lessen the burden on pilots during an already high-pressure event.

In the Havana incident, the crew flipped the affected No. 2 engine’s start lever to “cutoff,” closing the affected bleed valve 1 min. 16 sec. after the bird strike, the AVP memo stated. By then, the cabin was full of smoke.

In the New Orleans incident, the engine spooled down quickly following the bird strike, and the affected valve closed within 16 sec.

“Despite the PRSOV closure within 16 sec., this was not quick enough to preclude a toxic amount of smoke and fumes to enter the flight deck in high concentrations,” the AVP memo said. “During an LRD activation event, automatic bleed PRSOV shutdown cannot be relied upon with the current system shutdown logic. This is due to the amount of time required for N2 core speed to reduce, coupled with the possibility that the engine could attempt to continue relight procedures.

“The worst-case scenario is a left engine [(No. 1)] bird strike with LRD activation and without automatic PRSOV closure, which would reasonably lead to higher flight deck smoke concentrations,” the AVP memo added.

Among the concerns AVP cited was a Boeing analysis showing that an LRD activation can reduce flight deck visibility to 5 in. within 30 sec. if the PRSOV is not closed. This gives pilots a narrow window to keep the cockpit air clear. Given the hazards, current protocols are insufficient, AVP argued.

Some pilots agree. The applicable NCC—the Engine Fire or Severe Damage or Separation (EFSDS) list—is not a required memory item. The 737 has no warning light or prompt that differentiates a routine engine failure from one that triggers the LRD. Pilots must first identify the engine problem as “severe,” then reference a quick-access card or similar source to follow the steps.

“[LRD activation] presents itself buried under a bunch of different things,” says Dennis Tajer, spokesperson for the Allied Pilots Association and a 737 captain at American Airlines. “You have to analyze it, and you’re doing it when you’re close to the ground and your job is just to get the aircraft cleaned up. Then the [LRD] dumps a bunch of smoke into your office.”

The FAA and EASA acknowledged that LRDs need further review and potentially some changes—but not immediately.

“The FAA held a [CARB meeting] to discuss the CFM Leap 1B engine bird strikes leading to smoke entering Boeing 737 MAX aircraft,” the agency said in the statement. “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.”

EASA, which jointly certifies CFM products alongside the FAA, said the two agencies “concur on the line of action.”

While nothing will change on the LRD or in flight manuals, pilots will receive updated guidance. Boeing has issued “new information” with instructions “that direct flight crews more quickly to the appropriate actions when they experience abnormal engine indications,” the FAA said.

The FAA statement did not detail the new instructions, which are still working their way through airline flight operations departments and into pilots’ hands. Boeing did not immediately respond to an Aviation Week request for comment.

The decision does not ease pilot concerns.

“Boeing’s enhanced instructions better be some way to protect passengers other than running three separate checklists in seconds,” Tajer says.

The Cockpit Companion, an unofficial book and app for 737 system functionality, published its own LRD update. The update also suggests adding a new memory item to two NNCs: the EFSDS and Engine Failure or Shutdown lists. The action: Close the related bleed switch.

“This one just struck me right away,” Cockpit Companion co-founder Bill Bulfer says. “I told [co-founder Robert Dorsett], ‘This has to go out to the pilots, because this can happen anytime.’”

Another 737 MAX pilot who first brought the LRD issue to the FAA this year is proposing a similar change to the EFSDS.

While the FAA’s review found no immediate safety risks, the agency hinted that longer-term changes are likely.

One possibility is changing the system’s logic to ensure PRSOVs close more quickly following an LRD activation. The AVP report includes a similar recommendation.

Other aircraft types with LRDs also will be scrutinized to determine risk levels. “The FAA continues to assess how these events could affect other engines with similar structural designs,” the agency said.

The NTSB also will weigh in. The agency opened a formal probe into the New Orleans incident on Nov. 22 and has been participating in a Cuba-led probe of the Havana incident.

Meanwhile, EASA said it is conducting a longer-term “safety review” of LRDs on the entire Leap-powered fleet.

“The Leap 1A engine type includes a similar LRD device as installed on Leap 1B engines, and EASA is therefore investigating the scenario of a similar event occurring on Leap 1A engines installed on Airbus A320neo airplanes,” the agency confirmed, adding that no immediate safety issues have been identified. “EASA is evaluating, with the support of the engine and aircraft manufacturers, the risk levels to which the Leap 1A and A320neo fleet are currently exposed and whether corrective actions are required.”

The review will cover the 737 MAX and Comac C919 families as well as the A320neo, EASA said.

Engine failures that trigger LRDs are rare—the Southwest incidents are the only reported occurrences on the 737 MAX family. No reports have been filed from Airbus A320neos.

Various aircraft-engine combinations mean LRDs function differently. The Leap 1A LRD is generally similar to that of the Leap 1B. But on the Airbus A320/A320neo family, bleed air from both engines is mixed and fed equally throughout the flight deck and cabin.

The Leap 1A also has a larger fan diameter than the Leap 1B. Bird ingestion certification standards vary based on engine inlet size. Larger engines must meet more stringent standards, such as withstanding strikes by heavier birds.