What happened
On March 14, 2012, an Air France Boeing B777-20 and registration F-GUOB departed from Incheon International Airport. Approximately five minutes into the flight, the crew received an advisory message indicating that the right engine thrust was not meeting commanded levels. Following the malfunction, the captain decided to divert the aircraft back to Incheon.
During the descent, the crew performed necessary fuel dumping procedures to reduce the aircraft's landing weight. As the aircraft approached the runway, the situation escalated; at a radio altitude of 121 feet, an "ENGINE FAIL R" warning was displayed. The aircraft subsequently touched down safely at Incheon International Airport.
The investigation
The ARAIB investigation focused on the engine fuel and control system, specifically examining the main fuel pump, which had been replaced just two days prior to the incident due to a fuel leak. Investigators recovered a bolt from the interstage strainer and analyzed metal chips found within the fuel filter.
Laboratory analysis revealed that the metal chips contained elements—including aluminum, chromium, iron, and nickel—that matched both the recovered bolt and the engine's strainer gear. Further comparison showed that the bolt's dimensions and safety wire hole matched a bolt used on a maintenance bench support plate. The investigation established that the bolt had entered the fuel pump through the bypass return duct during a previous bench test and remained trapped in the strainer until it eventually damaged the strainer screen and the engine's gear set.