The Boeing 777X program suffered another setback last week when a static test airframe failed its final high-pressure load test, potentially resulting in a further delay to a project whose first flight date had already slipped due to earlier problems involving its General Electric GE9X engines.

The incident, first reported in the Seattle Times, happened on Thursday afternoon at Boeing’s widebody facility in Everett, Washington. The so-called ultimate load test forces the wings to bend to 150 percent of the maximum load they would likely encounter in flight while pressure gets applied to the skins of the wing and fuselage. In this case, a cargo door blew off its hinges under the extreme pressure, forcing Boeing to investigate the cause and possibly revisit design details. The overall testing program continues, however, according to a Boeing spokesman.

The latest incident comes less than two months after Boeing confirmed it had moved the target for first flight of the 777X to early next year from the second half of 2019 following consultations with engine maker GE, whose new GE9X encountered delays caused by a need to redesign a stator in the front part of the compressor that had shown more wear than anticipated during testing.

Still, at the time, Boeing CEO Dennis Muilenburg expressed satisfaction with the development headway Boeing has made with the rest of the 777X, calling it “one of the cleanest development programs that we’ve seen.” Although Muilenburg admitted to “some pressure” on the schedule, the program’s entry into service target officially remained the end of 2020.

About three weeks later, Boeing confirmed reports that it had slowed the development of the second version of the 777X—the 777-8—to “reduce risk.” While Boeing hadn’t yet disclosed a definitive certification schedule for the 350- to 375-seat 777-8, expectations that entry into service would happen before Qantas went ahead with plans to open routes from the east coast of Australia to London by late 2022 or early 2023 now have proved wrong.