What happened
While descending through FL250, the crew encountered an unusual vibration. In response to the vibration, the pilots reduced the aircraft's speed, which resulted in a decrease in the intensity of the shaking. During the flight, a flight attendant observed that a portion of the right wing was missing.
The aircraft subsequently landed without further incident and there were no injuries reported.
The investigation
Post-flight examination of the aircraft determined that 1.5 feet of the right aileron had separated while in flight. Records showed that this specific aileron had undergone a major repair in 1990, which included the replacement of both the skin and the core. This component was installed on the aircraft in 1992 without any additional work being performed on it.
Further inspection of the aileron revealed that there was very little flow of adhesive between the skin and the core. This condition was possibly caused by the use of an adhesive that was beyond its shelf life.