What happened
The flight crew operating a Boeing 727 experienced severe vibrations originating from the number three engine. Due to the intensity of these vibrations, the crew made the decision to shut down the engine while in flight.
The investigation
Following the incident, a detailed examination of the affected engine was conducted. The inspection revealed massive damage to the blades of the low-pressure compressor (LPC).
Investigators also examined the aircraft's interior and exterior conditions prior to the flight. It was discovered that the forward lavatory had been serviced before departure. During this servicing, the interior donut seal was found to be missing. As a result of this omission, blue fluid leaked from the lavatory system and covered the right side of the airplane.
Findings
The severe vibrations that necessitated the engine shutdown were directly linked to the mechanical failure of the low-pressure compressor blades. The root cause of this damage was traced back to the maintenance error in the forward lavatory. The absence of the donut seal allowed corrosive or lubricating blue fluid to escape and likely enter the engine intake or adjacent systems, leading to the catastrophic blade damage.