United Eyes Pratt-Powered 777 Return; Nacelle Fix Delays Persist

Damaged PW4000 engine
Credit: NTSB

United Airlines is hopeful that its grounded, Pratt & Whitney-powered Boeing 777-200s could be back in service later this year, but work on required changes, notably reinforced nacelle components, is likely to push necessary regulatory approvals to 2022.

“We’ve gone through an extensive set of analysis and testing of the engines in conjunction with our partners at Pratt & Whitney, Boeing and the FAA and are in the process of returning those aircraft to service,” United Chief Commercial Officer Andrew Nocella said during a Cowen-hosted investor conference Sept. 9. “We’d like to see those aircraft to go back up in the air sometime late this year, early next year and be ready for full flying by the spring of next year.” 

United has 52 PW4000-powered 777s on the ground—a sub-fleet that generated nearly 10% of its pre-downturn available seat miles, Nocella said. It was the only U.S. carrier operating Pratt-powered 777s when the fleet was parked, but Eastern Airlines recently purchased several from Japan Airlines (JAL) and plans to have them flying in 2022.

The global fleet of 128 777s with PW4000s has been grounded since late February following a failure onboard a United 777 near Denver—the third PW4000-powered 777 in-service event in three years linked to a cracked fan blade. In two of the events, both involving United aircraft, investigators confirmed damage from the blade failure caused parts of the nacelles to break away and strike the airframe. Little information has been released about the third event, onboard a JAL 777-200 in December 2020.

The FAA is working with Pratt on revised inspection protocols to address the fan blade issue, while Boeing has been tasked with developing nacelle modifications to strengthen the inlet and other components.

Agreement on updated inspection protocols is close and are expected to be mandated by the FAA this year, sources familiar with the matter told Aviation Week. The revised protocols will combine new ultrasonic inspections with Pratt’s proprietary thermal acoustic imaging (TAI) inspections that have been in place for the life of the program. The NTSB cited inadequate TAI inspection procedures and intervals as contributors to a 2018 in-flight engine failure of a United 777-200 en route to Honolulu that started with a fractured blade—the first of the three incidents that led to the grounding. 

The longer-term issue that must be addressed is nacelle modifications. Boeing has been working on nacelle changes since before the most recent in-flight failure. But the sources with knowledge of the situation confirm that the work is not likely to be done and approved before 2022. The FAA is not expected to approve any of the aircraft for revenue service until both issues are solved, the sources added.

Nacelle design and approval is a complex process that traditionally has taken several years. That was before new concerns about protecting the airframe from damage when engine failures are contained—meaning debris does not go through the engine structure and threaten the airframe—and occur during different phases of flight, not just when the engine is at full power, which is the current certification benchmark. 

The 777 failures and two 737 Next Generation events have changed how regulators view airframe-engine integration requirements and prompted Boeing to re-work nacelles for 777s and 737NGs. The 737NG work—design changes to inlets, fan cowls, and exhaust nozzles—began in 2019 and was once set to wrap up this year, but the timeframe has been pushed out to 2022 at least.

Boeing declined to comment on the timeframe for the fixes. “Boeing is working closely with the FAA, our customers and Pratt & Whitney to safely return PW4000-112-powered 777 airplanes to service,” the company said. “We have identified design changes and are working to finalize them, including a robust certification effort.”

Inquiries to the FAA and Pratt were not immediately returned.

Sean Broderick

Senior Air Transport & Safety Editor Sean Broderick covers aviation safety, MRO, and the airline business from Aviation Week Network's Washington, D.C. office.