Boeing has asked the Federal Aviation Administration to exempt its long-delayed 737 Max 7 from several certification rules due to an issue involving engine anti-ice system overheating.

The company, which has aimed to begin Max 7 deliveries next year, requested temporary exemptions in November as part of its effort to achieve the type’s certification, according to an FAA notice released on 4 December.

Boeing is working on a permanent fix. It remains unclear how the problem might affect the Max 7’s certification timeline but the exemption request makes clear the company needs more sign offs from the FAA.

“The… request is a part of the certification process. The FAA will determine when all certification requirements are met,” Boeing tells FlightGlobal.

Boeing and the FAA are familiar with the overheating problem, which can affect engine barrels and cowls. Earlier this year, the FAA issued an airworthiness directive addressing the risk in Boeing’s two in-service Max models – the Max 8 and Max 9. That order prohibits some operations and specifies when pilots are to use the anti-ice system.

Boeing 737 Max at Boeing field in Seattle on 14 June 2022

Source: Jon Hemmerdinger, FlightGlobal

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The FAA’s 4 December notice says Boeing requested “a partial exemption from [certain rules] as they relate to the engine nacelle inlet structure and engine anti-ice system” on 737 Max 7s.

Boeing seeks the exemption through May 2026.

“In November, we made a request to certify the 737-7 with the same inlet design and engine anti-ice system as the in-service 737 Max fleet,” Boeing says. “Under this request, operators would continue measures that were shared with them earlier this year and mandated by the FAA in August to mitigate potential overheating in a portion of the inlet structure under a very specific combination of weather and operational conditions.”

Specific rules from which Boeing wants the Max 7 exempted include those addressing extended overwater operations and the degree to which certain critical systems and components are unlikely to fail. Boeing also seeks temporary reprieve from a requirement that manufacturers account for environment conditions like temperature and humidity when ensuring material durability.

Boeing intends to permanently address the issue by developing and certificating “design changes necessary to address overheating during certain conditions that may result in failure of the engine inlet inner barrel”, the FAA notice says.

“We are developing a long-term solution, subject to FAA approval, that will go through testing and certification prior to being introduced to the entire 737 Max fleet,” Boeing adds.

The FAA did not respond to a request for comment.

Exemption requests are not uncommon during certification programmes. This year the FAA granted the Max 7 a separate exemption related to lightning and radiation protection rules.

Whether Boeing may seek similar exemptions for its 737 Max 10, which has also not yet been certificated, remains unclear. The company did not address questions about the Max 10.

In July, Boeing said it expected its Max 7, the smallest Max variant, would be certificated in 2023, but that its first delivery of the type would come in 2024. It also aimed to deliver the first Max 10, the largest variant, in 2024. Both types are years behind schedule due to factors including increased regulatory scrutiny following the Max 8 and 9 groundings several years ago.

Boeing executives in October said the company’s timelines remained unchanged. But in November, Reuters reported that the Max 7’s top buyer, Southwest Airlines, expects the FAA will not clear the type until April 2024, and that Southwest would not start operating it until October or November next year.

The overheating issue came to light in August when the FAA published the Max 8 and Max 9 directive. The problem can occur if the engine anti-ice system is activated in dry air for more than 5min when operating in conditions involving specific combinations of altitude, air temperature and thrust settings, the FAA said. As a result, the engine’s inner barrel can overheat and fail, which can damage the engine cowl.

The FAA’s order requires airlines update flight manuals to prohibit pilots from using the engine anti-ice system when not in actual icing conditions and when not anticipating icing.

GE Aerospace stressed in August that CFM International Leap-1B engines, which power 737 Max, are not part of the problem. GE Aerospace co-owns CFM with Safran Aircraft Engines.