What happened
On August 30, 2002, a Fokker 100, registration PT-MQH, operated by TAM Transportes Aéreos Regionais, was performing a scheduled flight from Guarulhos to Campo Grande. While cruising at FL 350, the crew observed "FUEL FILTER" and "FUEL PRESSURE LOW" warnings for engine number 2.
Following established procedures, the crew activated the crossfeed valve to supply fuel from the left tank to the right engine. However, this led to a significant fuel imbalance and an accelerated rate of fuel consumption. As the aircraft descended toward Araçatuba, the fuel loss became critical. Approximately 16 NM from the airport, both engines flamed out, forcing the crew to execute an emergency landing in a pasture at Fazenda Birigui. The aircraft sustained heavy damage to the fuselage, wings, and landing gear, and was subsequently deemed a total loss. While the crew and 20 passengers evacuated safely, four passengers sustained minor injuries.
The investigation
CENIPA investigators examined the wreckage and focused on the fuel system of engine number 2. The investigation identified that the "LP FUEL TUBE," which connects the fuel flow meter to the high-pressure fuel pump, had disconnected from the pump. This disconnection was caused by the wear of the metal retaining ring (inner shoulder) of the retaining plate.
Technical analysis revealed that the tube, made of 18/8 stainless steel, and the retaining plate, made of aluminum alloy, were subject to abrasive wear due to engine vibrations. Metallographic examinations showed that the tube was not installed concentrically, leading to localized high stress. Furthermore, testing of existing stock revealed that several replacement tubes also exhibited dimensional variations from the master standard, indicating manufacturing inconsistencies.
Findings
- Design deficiency: The use of dissimilar metals (stainless steel and aluminum) in a high-vibration area facilitated the wear of the softer aluminum component.
- Manufacturing deficiency: Variations in the dimensions of the fuel tubes compared to the master standard contributed to improper fitment.
- Operational limitations: The aircraft's Quick Reference Handbook (QRH) did not include specific emergency procedures for an in-flight fuel leak, and such scenarios were not included in simulator training.
- Maintenance visibility: The wear on the retaining ring was not detectable during intermediate inspections and could only be identified during a major engine overhaul.