Fuel contamination has been confirmed as the cause of a double engine malfunction on a Cathay Pacific Airbus A330-300 on approach to Hong Kong International airport (HKIA) in 2010.
In a final report released on 4 September, Hong Kong's Civil Aviation Department (CAD) says that 24.4t of contaminated fuel was uplifed into the aircraft at Surabaya's Juanda International airport. This caused "stiction" - static friction - in the fuel metering unit of both engines, leading to the total seizure of these components and the loss of thrust controls of the aircraft during approach to HKIA.
It found that though the aircraft was uplifed with the proper grade of fuel, it was contaminated with super absorbent polymer (SAP) spheres. During the flight, some SAP spheres were trapped in the fuel metering unit on both engines, causing stiction in the unit that resulted in engine pressure ratio fluctuations.
SAP spheres contain carbon, oxygen, sodium, chlorine and sulphur.
Investigations led the CAD to the hydrant refuelling circuit serving 10 stands at Surabaya airport, which had undergone extension work as part of an apron extension project.
Fuel samples collected from the reworked hydrant after the accident contained salt, likely because salt water had entered the system during the extension work - Surabaya airport is located near the sea. The re-commissioning process of the reworked hydrant was also not properly coordinated, which led to the premature resumption of the hydrant refuelling operations, says the CAD.
The report also apportions some blame to the airport personnel uploading the fuel. SAP in the dispenser's filter monitors reacted with salt water in the fuel to create a gel, which caused an increase in differential pressure indication and vibration of the refuelling hose.
Although personnel observed an unusual vibration during the refuelling, they failed to stop the procedure and investigate the cause of the vibration. The affected aircraft, registration B-HLL, was operating flight CX780 when both its Rolls-Royce Trent 700 engines malfunctioned on 13 April 2010. The crew had to issued a Mayday call and eventually landed at a high ground speed of 231kt, causing the lower cowling of one engine to contact the runway surface and brake overheat that deflated five tyres after the aircraft stopped. Passengers were evacuated using escape slides.
PT Pertamina, which carried out the refuelling at the airport, has since taken several measures to prevent a similar incident, including training for their refuelling personnel and has also installed automatic differential pressure monitoring devices on its fuelling dispensers. ICAO, meanwhile, has issued a manual on civil aviation jet fuel supply to provide guidance on internationally accepted practices.
CAD has also made an additional safety recommendation for ICAO to specify the need to install a device in the equipment used in refuelling aircraft. This equipment should alert the operator and stop the refuelling process when the differential pressure across the equipment filtration system is out of the designated range.