N148UA 747SP United ( c/n: 21648 )
United 747SP N148UA departed EWR at noon with destination Tokyo on April 29 1991, carrying only 84 passengers.
The aircraft climbed normally and reached it’s cruising level at FL350. It then accelerated from Mach .81 to M .85 and during the acceleration a vibration was felt in the cockpit and cabin.
No abnormal engine readings were observed.
The vibration lasted for about 2 minutes and was followed by a loud bang heard in the cockpit.
The aircraft landed safely and normally.
The number 2 engine revealed a failed sixth rotating airseal.
Metallurgical examination of failed airseal showed features typical of overstress with no indication of preexisting cracks.
Source & Reports
Read the report here (pdf).
Read the brief here (pdf)