FAA Clears Boeing to Start TIA Phase 4B Testing on 777X

Boeing has received Federal Aviation Administration (FAA) approval to proceed with type inspection authorization (TIA) phase 4B certification testing for the 777X, a critical piece of securing type certification of the long-delayed widebody airliner derivative. The milestone was revealed to Leeham News and Analysis in a June 6 interview with Stephanie Pope, chief executive of Boeing Commercial Airplanes.

“This authorization unlocks the largest remaining portion of our flight test with the FAA that we can now go execute," she explained. "It enables further avionics and stability and control testing, as well as human factors flight testing."

According to Boeing, TIA-4B flight testing on the 777X is not yet complete, but the bulk of work in other phases of the TIA process is done.

"There're five TIAs that we have to work through," Pope said. "4B is the last with what I'd say is a significant amount of work, predominantly focused on systems like avionics. We just got the approvals to go complete that work, which is a big milestone."

Heightened Scrutiny

TIA is typically a one-step authorization, but the FAA decided to grant it in stages for the 777-9 aircraft. This was as a result of the agency stepping up scrutiny of Boeing's aircraft development programs following the 737 Max crashes of 2018 and 2019.

Type certification of the 777X is not imminent. Boeing maintains that it is on track to achieve that milestone next year, about seven years after the company originally expected to start delivering 777-9s to customers.

Precisely how much longer Boeing's 777X flight-test program will last is unclear. The FAA will likely require hundreds more test points before issuing a type certificate.

Four 777X test articles have flown thousands of hours to date, though the test fleet was grounded for several months starting in August 2024 due to thrust-link stress fractures found during inspections. Boeing maintains that redesigning and replacing affected components has resolved the thrust link fatigue issue.

Certification of the 777X is viewed as critical to Boeing's efforts to regain its competitive position in the large twin-aisle aircraft segment. It has been losing ground to the Airbus A350-1000, which entered service in February 2018 as the largest member of the A350 family.

Leeham News and Analysis is part of the AIN Media Group.