What happened
On March 21, 2022, a Boeing 787 operated by Uzbekistan Airways, registration UK78701, was performing flight NU512 from Seoul to Tashkent. During the initial taxi phase at Seoul Incheon International Airport, the crew observed an "ENG REVERSER L" message on the EICAS, along with several status messages related to the left engine systems. Following consultation with maintenance personnel, the aircraft returned to the stand, where it was determined that a failure in the Left Engine Data Concentrator (MEDC) Channel A had triggered the erroneous alerts. After technical staff performed necessary deactivation procedures and verified the aircraft's airworthiness under the MEL, the flight resumed.
During the subsequent flight, while climbing through FL360 and leveling off at the cruise altitude of FL401, the crew heard a loud pop. This was immediately followed by the visible cracking of the left forward cockpit window and subsequent sparking. The crew promptly executed the required checklists for window damage and requested a descent to reduce aerodynamic loads on the damaged component. The aircraft returned to Seoul and performed a safe landing on runway 33R.
The investigation
The investigation examined the maintenance history, crew statements, and technical components of the windshield assembly. Investigators reviewed the aircraft's logbooks, which confirmed the occurrence of the crack at FL401. A physical inspection of the removed windshield (part number 190800-15) revealed no evidence of external mechanical impact or foreign object damage.
Technical analysis included a review of Boeing's global reliability data for this specific windshield part number. It was noted that while the aircraft's total time in service was approximately 15,524 hours—consistent with the fleet average—the investigation also identified an outstanding deferred defect regarding the repair of a window seal, which had been managed under manufacturer-approved intervals.
Findings
- The primary cause of the event was the structural failure (cracking) of the left forward cockpit window.
- The investigation concluded that the crack was due to a design or manufacturing defect rather than external impact or improper maintenance.
- The crew's decision to return to the airport was in full compliance with the Boeing 787 Flight Crew Operating Manual (FCOM) procedures for window damage.
- The earlier engine reverser alert was unrelated to the windshield failure and was caused by a faulty data concentrator.