Flight Operational Assessment of Hybrid Laminar Flow Control (HLFC) Aircraft

Hybrid Laminar Flow. Control (HLFC) offers the potential for significant fuel burn reductions. However the system is likely to have a lower operational reliability than other aircraft systems. The “failure modes” which will result in a loss of laminar flow, are mechanical (i.e. system failure) and environmental (i.e. rain, ice or insect contamination). The typical contingency fuel taken onboard to accommodate unplanned contingencies is 3 to 5% of the trip fuel. This is inadequate to cover a complete loss of laminar flow for an extended period during the cruise. The probability of an in-flight diversion decreases as the planned contingency fuel is increased; however this leads to a reduced fleet efficiency due to increased take off weights. A computer performance model of a twin engine aircraft in the class of the Boeing 757, has been used to study the change in block fuel for alternative fuel planning assumptions based on a loss in laminar flow due to cloud encounters in the cruise.