A Cracked Seal in a Test Engine Just Pushed Boeing's 777X Deeper Into 2027
A durability fix now has its own certification clock
Boeing's long-delayed 777X program has picked up a new, narrower complication this week, layered on top of a timeline that was already sliding toward 2027. GE Aerospace, which builds the GE9X engines that power the 777X, has confirmed it has begun shipping production engines fitted with a redesigned mid-seal component, the fix for a durability issue first discovered during a January 2026 shop visit when engineers found a crack in the part on a flight-test engine.
GE says the underlying issue does not, on its own, threaten Boeing's existing 2027 first-delivery target. But the redesigned seal now needs its own separate approval from the Federal Aviation Administration, a parallel certification track that adds one more moving piece to a 777X program that has already spent years working through flight testing, ETOPS trials and a series of schedule resets. GE Aerospace Chief Financial Officer Rahul Ghai said this week that the company is "working with the FAA on certification" of the modified part, according to reporting on the update.
What actually broke, and what GE has done about it
The GE9X is the largest and most powerful commercial jet engine ever built, sized specifically for the 777X's twin-engine widebody design. The mid-seal is an internal engine component tied to durability under sustained operating conditions rather than a flight-critical structural part, which is why GE and Boeing have both characterized the issue as a durability finding rather than a safety event grounding the test fleet.
GE first disclosed publicly in February that it was studying a potential durability issue with the seal, after the January shop-visit discovery. By April, the company said it had traced the root cause and was finalizing a redesign. That redesign has now moved from validation into production: GE began shipping engines equipped with the new seal to Boeing during the third quarter of 2026, according to the company's latest disclosures, and says it has completed its own internal testing of the modified component ahead of seeking FAA sign-off.
Crucially, GE has said the existing, unmodified mid-seal is expected to be sufficient to support the certification work still needed to reach ETOPS approval — the extended-range twin-engine operations testing that allows a twin-engine widebody to fly long overwater and remote routes on two engines. That distinction matters because it suggests the seal issue and the ETOPS timeline are, for now, running on separate tracks rather than one blocking the other outright.
Seven years behind, and counting
The 777X's troubles did not start with this seal. The aircraft was originally targeted to enter service in 2020, and the program is now roughly seven years behind that original schedule, having worked through an earlier structural finding on a wing-to-body join, pandemic-era demand shifts, and a series of FAA scheduling and process delays that have compounded each other. Boeing already took a $4.9 billion charge in October 2025 when it pushed the first delivery date to 2027.
FAA Administrator Bryan Bedford has indicated that 777X certification work is effectively queued behind the agency's ongoing certification of the 737 MAX 7 and MAX 10 variants, both of which the FAA and Boeing have been targeting for approval before the end of 2026. Boeing Chief Executive Kelly Ortberg has said the company expects to finish the bulk of its 777X flight test program by the end of the year, "with the exception of ETOPS," which is expected to extend into 2027 regardless of the seal issue. Boeing and GE have both maintained that the delays reflect certification process and testing sequencing rather than a newly discovered safety-critical flaw in the aircraft.
What it means for launch customers
More than 620 777X aircraft are on order across Boeing's widebody customer base, led by Emirates with 270 aircraft, Qatar Airways with 124, and Cathay Pacific with 35. Lufthansa, the launch customer, had been anticipating early deliveries once the aircraft cleared certification, but that timeline has already slipped and now carries additional uncertainty tied to the seal fix's separate approval path.
In the meantime, airlines holding large 777X orders have extended the operating lives of older widebody aircraft — including 777-300ERs and, in some cases, Airbus A380s — to cover the capacity those jets were originally meant to replace. That has meant additional maintenance costs and continued reliance on less fuel-efficient aircraft for carriers that had planned their long-haul fleet renewal around 777X delivery dates that have now moved multiple times.
The extended timeline has also given Airbus room to position its A350-1000 as a lower-risk alternative for carriers weighing long-haul widebody orders while Boeing works through 777X certification. Airbus has not needed to publicly campaign hard on this point; the schedule gap has done much of that work by itself, and several airlines with mixed widebody strategies have used the extra time to reassess how much of their long-haul growth to route through the A350 program instead.
Separately, roughly thirty 777X aircraft that Boeing has already built are sitting "at risk" — assembled ahead of final certification but potentially requiring rework to match the configuration that ultimately receives FAA sign-off. Some customers have indicated they would prefer to wait for new-production aircraft built to final certified specifications rather than accept early-build frames that need retrofitting, a preference that could affect how quickly Boeing can convert its order backlog into revenue once certification does clear.
Why the FAA's queue matters as much as the engine
Much of the 777X's remaining schedule risk has less to do with any single technical finding and more to do with how the FAA sequences its certification workload. The agency is simultaneously working through final certification of the 737 MAX 7 and MAX 10 — variants that have been in the certification pipeline for years in their own right — and has signaled that 777X work, including ETOPS approval, follows behind that MAX work in priority. That queuing effect means that even if GE's seal fix and Boeing's flight test program proceed without further surprises, the 777X's certification date is partly hostage to how quickly the FAA closes out the MAX 7 and MAX 10 files first.
This dynamic has become a recurring theme in Boeing's post-2024 recovery: a leaner, more heavily scrutinized FAA certification process, put in place after the door-plug blowout on a 737 MAX 9 and the broader quality-control reckoning that followed, has meant that every Boeing program now moves through certification more slowly and with more documentation than in years past. Industry analysts tracking the program have described the current 777X slippage as consistent with that broader pattern rather than a sign of a new, isolated crisis — but the cumulative effect is still a program now seven years removed from its original 2020 service-entry target, with a growing list of components and process steps that all have to close out in sequence before the first customer aircraft can be handed over.
The financial and competitive backdrop
Boeing's $4.9 billion charge tied to the October 2025 delivery push already reflected the cost of holding partially built aircraft, retraining production and delivery teams around a shifting schedule, and compensating some customers under contractual delivery-delay terms. Additional slippage tied to ETOPS and the seal certification would not automatically trigger a new charge of similar size, but it does extend the period during which Boeing is carrying inventory and overhead costs on a program that has not yet started generating delivery revenue at scale.
For GE Aerospace, the mid-seal issue is a relatively contained engineering problem inside a program — the GE9X — that the company has otherwise touted as a technical showcase, given its status as the largest and most powerful commercial jet engine ever certified. GE's public framing has consistently separated the mid-seal issue from any broader concern about the engine's core architecture or performance, and the company's decision to keep shipping engines with the older seal design for aircraft not yet requiring the fix — while simultaneously ramping up production of the redesigned part — reflects an attempt to avoid slowing Boeing's assembly line any further while the fix works through its own approval.
The competitive read-through for Airbus is real but limited. The A350-1000 competes with the 777X in the very-large-widebody segment, and every additional quarter of 777X uncertainty gives Airbus another opportunity to court airlines weighing long-haul fleet decisions. But most of the 777X's more than 620 orders come from carriers — Emirates, Qatar Airways, Cathay Pacific and Lufthansa chief among them — that have already committed heavily to the Boeing program and have limited near-term appetite to unwind those orders in favor of a competing aircraft, even amid continued delays. The more likely effect is incremental: some carriers stretching out older aircraft leases or extending maintenance programs a bit further, rather than wholesale order switching.
What to watch next
The near-term milestone to watch is FAA approval of the redesigned mid-seal, which GE expects within months of beginning deliveries of the modified engines, alongside the FAA's parallel work certifying the 737 MAX 7 and MAX 10 — the queue Administrator Bedford has said the 777X sits behind. Boeing has not revised its public 2027 first-delivery target in response to the seal finding, and GE has explicitly said it does not expect the issue to push deliveries out further. Whether that holds will depend on how cleanly the two certification tracks — ETOPS testing on the existing seal, and separate approval of the redesigned part — come together over the next several months, and on whether the FAA's broader MAX certification queue moves on the timeline Boeing and the agency have both signaled.