The US Federal Aviation Administration (FAA) has raised concerns over potential overheating issues that could affect CFM International-manufactured engines powering Boeing 737 MAX aircraft. The agency has identified that this issue could impact 1,187 aircraft globally, including 402 aircraft registered in the United States.
According to Airworthiness Directive (AD) 2023-15-05, issued on August 10, 2023, the FAA received a report in June 2023. This report indicated that flight testing and analysis revealed a specific problem. If the engine anti-ice is used in dry air for more than five minutes during certain combinations of altitude, total air temperature, and N1 settings, it could result in engine inlet cowl temperatures going beyond design limits when not in visible moisture.
The AD states, “Excessive heat buildup can cause overheat of the engine inlet inner barrel beyond the material design limit, resulting in failure of the engine inlet inner barrel and severe engine inlet cowl damage.” It’s important to note that there have been no reports of in-service failures of the engine inlet inner barrel so far.
Potential Risks and Boeing’s Response
The FAA warns that if this issue is not addressed, it could lead to “the departure of the inlet” and potential fan cowl failure and detachment from the plane. The consequences could be severe, including fuselage and/or window damage, potential decompression, and hazard to passengers seated near the window aft of the wing. It could also cause impact damage to the wing, flight control surfaces, and/or empennage, possibly resulting in loss of control of the airplane. The AD further explains that inlet loss could cause increased aerodynamic drag and asymmetric lift, risking fuel exhaustion on certain flights, and leading to a forced off-airport landing and injury to passengers.
An FAA spokesman clarified, “The FAA issued an immediately effective Airworthiness Directive for Boeing 737 airplanes equipped with CFM Model LEAP-1B engines.” The directive aims to address the use of the engine anti-ice system, which can cause the engine inlet inner barrel to overheat under specific operational and environmental conditions.
Boeing acknowledged the issue, stating that in “a very specific combination of weather and operational conditions,” the engine anti-ice system could create a situation where the inlet structure exceeded its maximum design temperature range. While the affected parts are manufactured in-house, Boeing only recently identified the problem “as part of our design analysis.” The risk was described as a “theoretical possibility” and was unlikely to impact deliveries. Boeing has developed mitigations and is working with impacted airlines to implement them, awaiting operational guidance and a more permanent solution.
The FAA’s identification of potential overheating in CFM engines on 737 MAX aircraft is a proactive step in ensuring aviation safety. While no in-service failures have been reported, the directive aims to address the issue promptly.
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