Boeing Adds Crosswind Tests To 777-9 Milestones

Boeing’s effort to earn regulatory approval of the 777-9 in time for deliveries to start next year continues to check off key certification requirements, with crosswind testing serving as a recent notable step.

The company recently took advantage of extreme weather conditions in Northwest Texas to conduct crosswind testing with the first 777-9, WH001. The tests, which took place in mid-March, were confirmed by the company in an internal message and video shared to social media April 29.

Boeing was eager to satisfy certification requirements for take-off, landing and maneuvering in high winds up to 60 kts as the 777-9 at 252 ft. 9 in. in length is the longest airliner yet built resulting in an empennage with a significant moment arm. For FAA Part 23 requirements, Boeing has to demonstrate satisfactory controllability during landings with a 90-degree crosswind component of at least 20% of stall speed.

“The conditions are pretty rare,” 777 Deputy Chief Pilot Heather Ross said, adding that Boeing meteorologists must look ahead for weeks to find the right mix of weather and airport layout. “Everything has to come together perfectly. That means having the airplane ready to go, and pilots that have practiced the extreme scenarios in the simulator as a team.”

Away from the crosswind tests, which took place at Lubbock Airport, Texas, WH001 has also conducted certification brake tests, much of which has been based at Clinton-Sherman Airport, Oklahoma. Tests at the airport, which has a 13,500 ft.-long main runway, were focused on the stopping performance of the RTX Collins-supplied carbon disc brakes, which are lighter than the older, steel alternative.

Originally awarded to RTX predecessor UTC in 2015, the 777X brakes are made of Duracarb—a proprietary carbon material developed by Collins heritage company Goodrich—which can absorb high thermal energy loads equal to brake surface temperatures up to 5,000° F without failing during an emergency runway stop.

In another signal of the program’s rising test tempo, 777-9 WH004—the fourth development aircraft—is also being reactivated for flight. The aircraft, which is expected to be fitted with a full passenger interior, has not flown for almost 3.5 years.

The 777X flight test program has amassed more than 1,300 flights and 3,800 flight hours. FAA-required flight testing began in July 2024 but paused in August to address an engine thrust link issue. Flights resumed in January, and the FAA has expanded Type Inspection Authorization (TIA) to cover more extreme testing requirements.

Under TIA, each set of exercises takes place only after the FAA is convinced the system being tested meets the regulations and is safe to trial. For each project, the FAA determines whether TIA will be phased—as is the case with the 777-9—and if so, what each phase will include.