The US Federal Aviation Administration (FAA) is unlikely to recertify Pratt & Whitney PW4000-powered B777s for revenue operations before early 2022, the Wall Street Journal has reported.

While the FAA would not comment on the ongoing work, it is expected to conclude its investigation into a February 2020 incident within a few weeks. Given an engine blade failure caused an uncontained engine failure and fire during a B777-200's climb out from Denver International, the regulator will likely mandate additional requirements for the powerplants which could entail both a revised inspection routine and physical changes to engine covers. Implementing the changes is expected to take longer than previously anticipated, however.

"We are working closely with the FAA, our customers and Pratt & Whitney to safely return PW4000-112-powered B777 airplanes to service. We have identified design changes and are working to finalize them, including a robust certification effort," Boeing told Reuters in a statement.

The ongoing grounding is a particular nuisance to United Airlines, the only operator of the PW4000-powered B777-200s and B777-200ERs in the United States. In contrast to JAL - Japan Airlines, which retired all affected aircraft shortly after the February grounding and ANA - All Nippon Airways which retired most, United Airlines is committed to returning them to service for trunk hub-to-hub domestic services in the US, as well as flights to Hawaii.

Other operators of PW4000-powered B777s include Asiana Airlines, Jin Air, and Korean Air, the ch-aviation fleets module shows. Ukraine International Airlines has a single such aircraft but is unlikely to return it to service due to its general fleet cuts.