(Bloomberg) -- Boeing Co. is racing to complete a key engineering fix needed to certify the smallest version of its cash-cow 737 Max jetliner after a US lawmaker convinced the planemaker not to pursue a safety exemption.

A redesign for the Max 7’s engine inlet de-icing feature could be ready within nine months, Chief Executive Officer Dave Calhoun said Wednesday. The embattled company will devote additional engineers and resources to potentially accelerate the work.

“We’ll step up resources, we’ll step up whatever testing is required, we will do everything we can” to help get the long-overdue model approved to fly, he said on a conference call to discuss fourth-quarter earnings. Calhoun declined to discuss certification timing, saying that was up to the US Federal Aviation Administration.

The comments offer insight into a critical issue for customers of two yet-to-debut variants of the narrowbody jet — the Max 7 and the larger Max 10. Concerns have grown that those models could face further delays under the intense scrutiny of Boeing’s manufacturing practices in the wake of the near-disaster on a 737 Max 9 operated by Alaska Airlines earlier this month.

Read More: Boeing’s 737 Max Models at Risk of Delays Amid Federal Scrutiny

Last year, Boeing said the Max 7 could be certified in early 2024 while the Max 10 could be approved by late 2024 or early 2025. Eventually delivering those planes are key pieces of Boeing’s plan to generate $10 billion of free cash flow by 2025 or 2026.

Customers have already started bracing for the timing to slip. Southwest Airlines Co., which has the largest Max 7 order book counting roughly 300 planes, said last week it no longer expects to receive the variant this year. United Airlines Holdings Inc. removed the Max 10 from its internal plans due to the uncertainty.

The engineering change is needed to address a flaw with the plane’s engine de-icing system. Boeing said this week that it withdrew a request for a safety exemption for the system, a move seen as likely to further delay the plane.

Calhoun said Wednesday that he decided to withdraw that request after meeting with Senator Tammy Duckworth, who has criticized Boeing’s pursuit of the exemption. The Illinois Democrat and former US Army helicopter pilot questioned why the company wanted an exemption when a permanent fix was only months away. Calhoun said he sounded out a key customer, spent the weekend thinking it over, and in the end was won over by Duckworth’s stance.

“Why is that the right call?” Calhoun said, recalling the senator’s comments. “In my view, it was a sound, principled position to take.”

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