Pratt & Whitney Gets Partial Exemption For PW4000 Redesign Approval

Pratt & Whitney’s changes to its 112-in. engines to address fan blade failure risks revealed in three in-service incidents will not require a key certification test to demonstrate compliance with an FAA rule, but the manufacturer must show the new design meets the rule’s requirements, the agency said.

The FAA on March 26 granted Pratt partial exemption from a fan-blade out test required to meet 14 CFR Part 33.94 as part of an engine’s type certification. The test requires demonstrating a blade failure “at the outermost retention groove”—at the blade’s root—will not trigger an engine fire or mounting attachment failure.

Pratt in August 2025 asked the FAA for an exemption to the test for its modified engine design, proposing instead to use a model assuming a failure farther from the root, along the airfoil.

The FAA’s exemption says Pratt does not have to conduct new physical tests that the original design passed in 1994 during its certification program. But the manufacturer must use modeling to show its new design both corrects the unsafe conditions, including engine flange separation and fire, and meets Part 33.94’s containment requirements assuming a failure along the airfoil.

“Furthermore, [Pratt] must show that the redesign has improved or maintained the containment (blade containment and mounting attachment) capability that was demonstrated in the original certification test,” the FAA’s decision said.

Pratt’s redesign addresses risks revealed in three in-service events in 2018-2020.

In each event, a fan blade—or first-stage low-pressure compressor blade on the PW4000 series—fractured due to fatigue cracking. The failure sent blade fragments into the nacelle’s forward inner surfaces and triggered a chain reaction that directed debris into the airframe and wings.

Each failure occurred along the blade’s airfoil, not at the root. A PW4000 has never experienced a fan blade failure at the root, Pratt told the FAA in its exemption request.

The events—two involving United Airlines Boeing 777-200s, in February 2018 and February 2021, and one on a Japan Air Lines 777-200 in December 2020—spotlighted unrecognized risks of airframe damage that were not exposed during the original certification testing. The 2021 event included an engine fire.

The FAA grounded the affected 777 fleet—about 130 aircraft—in 2021. Boeing, Pratt, and the FAA developed a return-to-service plan that included regular inspections and eventual design changes. United Airlines is the lone operator of affected 777s.

All three fan-blade failure events that led to the grounding and redesign effort involved PW4077 engines. Pratt’s analysis determined that the latent unsafe conditions apply to the PW4074, PW4074D, PW4077, PW4077D, PW4084D, PW4090, and PW4090-3 models.

The FAA reviewed its nacelle certification requirements in response to the 777 incidents and two involving CFM56-7B-powered 737-700s. The agency determined its regulations are sufficient, but manufacturers needed better guidance on how to comply with the requirements.