Near Simultaneous Engine Rollbacks are very rare. One possible explanation under very similar environmental circumstance. This accident involving Rolls Royce Trent 800 Engines on a 777 on a Beijing to London flight in 2008. The AAIB issued a full report on 9 February 2010. It concluded:
“
The investigation identified that the reduction in thrust was due to restricted fuel flow to both engines.
The investigation identified the following probable causal factors that led to the fuel flow restrictions:
Accreted ice from within the fuel system released, causing a restriction to the engine fuel flow at the face of the FOHE, on both of the engines.
Ice had formed within the fuel system, from water that occurred naturally in the fuel, whilst the aircraft operated with low fuel flows over a long period and the localised fuel temperatures were in an area described as the 'sticky range'.
The FOHE, although compliant with the applicable certification requirements, was shown to be susceptible to restriction when presented with soft ice in a high concentration, with a fuel temperature that is below −10 °C and a fuel flow above flight idle.
Certification requirements, with which the aircraft and engine fuel systems had to comply, did not take account of this phenomenon as the risk was unrecognised at that time.
”
— AAIB, Report on the accident to Boeing 777-236ER, G-YMMM, at London Heathrow Airport on 17 January 2008