CERTIFICATION FLIGHT-testing of the Rolls Royce Trent-powered Boeing 777 has resumed after engineers tackled a rear-bearing vibration problem caused by "distress of the aft-strut fairing and primary nozzle".
The test programme has been held up for "about a week", says Boeing, which grounded the aircraft in the first week of September to investigate an unusual engine tone, later traced to the rear bearing. Ground tests to determine the cause of distress of the aft-strut fairing and primary nozzle "...created some vibration stress on the rear engine bearing", says Boeing.
The cause of the strut-fairing and nozzle distress, which then transferred damaging loads to the bearing, was found to be a previously undetected aerodynamic disturbance in the airflow between the fairing itself and the primary nozzle. Boeing, which is responsible for the strut and nacelle, and R-R hope that the problem will be resolved by reducing the space between the two and cutting the airflow and related disturbance.
Boeing was scheduled to resume full certification tests with a negative-G test flight on 15 September. It says: "We're still on schedule for certification in early 1996."
Source: Flight International
