GE Aerospace Addresses GE9X Turbine Mid-Seal Issue to Keep Boeing 777X Certification on Track
Why It MattersThe fix shifts 777X program risk from airframe certification to propulsion, and retrofit costs already led Emirates, Lufthansa and United to decline roughly 20 built airframes.
GE Aerospace is finalizing a redesign of the mid-turbine seal in its GE9X engine, the exclusive powerplant for the Boeing 777X, after a crack was discovered during a shop visit on a flight-test engine. The seal sits between turbine stages where temperatures exceed 1,000 degrees Celsius; the crack was found on a test unit rather than a production engine, and final modifications are still underway.
Starting in February, GE began on-wing inspections of legacy mid-seal components and carried out corrective actions for each affected unit under FAA oversight. Boeing has confirmed that 777X flight testing has continued uninterrupted throughout the process, and GE's Q1 and Q2 earnings calls confirmed that tooling changes are underway, suppliers are ramping production of the revised component, and the modification is in finalization.
The GE9X is the world's largest turbofan, with a 134-inch fan, and the redesigned seal is meant to improve thermal balance, turbine efficiency and long-term durability. GE Flight Plan data projects shop-visit intervals of 10,000–12,000 cycles, and a more robust seal could extend those intervals or reduce unscheduled engine removals. Engines delivered to Boeing for early 777-9 customer aircraft will incorporate the new part, while existing engines will require a retrofit — a factor that contributed to Boeing's earlier difficulty this year in placing about 20 already-built 777X airframes with committed carriers, after Emirates, Lufthansa and United declined those aircraft citing high retrofit costs and structural repairs needed on airframes that had sat idle for eight years.
GE and Boeing remain on schedule with the mid-seal updates, and the FAA certification timeline appears to remain intact. Boeing is maintaining a 2027 first-delivery target, with GE set to deliver the first batch of production GE9X engines in late 2026 to early 2027; if those engines incorporate the redesigned seal and pass FAA conformity inspections without issue, Boeing's delivery schedule holds. Analysts at Leeham News have noted that propulsion issues are now the primary development priority for the 777X program rather than airframe certification, and GE's next earnings call and FAA certification updates will indicate whether the redesign is tracking toward service entry.
