Incident Description
During the climbout phase of flight, the flight crew detected an airframe vibration. All engine gauges, system readouts, synoptic pages, and airplane controls indicated normal parameters. The crew contacted their maintenance base and attempted to troubleshoot the issue but could not determine the source of the vibration. The vibration remained consistent and unchanged as the aircraft continued its climb and subsequent approach.
Resolution of Vibration
When the airplane leveled off at 7,000 feet during the approach, the crew felt a distinct bump, after which the vibration ceased entirely. The aircraft landed without further incident and taxied to the gate normally.
Post-Flight Findings
A post-flight inspection revealed that the number 1 exhaust fairing was missing. Additionally, a dent was found on the left aft fuselage. Further examination showed that all 30 bolts that would have attached the exhaust nozzle assembly to the exhaust frame were missing "without a trace."
Previous Maintenance History
Seven months prior to this incident, the tailpipe had been found loose. In response, ten bolts were replaced and the remaining bolts were re-torqued. The most recent inspection of the airplane had been completed approximately two weeks before the incident, about 105 flight hours earlier.
Related Observations and Actions
Company personnel had previously encountered cracked bolts on exhaust flanges from other engines. Laboratory examination of used bolts from another engine revealed no anomalies. Following this incident, the engine shop buildup and shop exit manuals were revised to make the installation and torquing of exhaust nozzle bolts a required inspection item.