Speed optimization is one of key areas affecting airline operational efficiency with potential to save operational costs in order of tenths of percent. It translates to very significant amount of money when accumulated over year of operations for example. Surveys are indicating that many airlines are still not getting the full potential out of speed optimization so we decided to write short article to provide overview of best practices and tools available in NAVsystem.
Basic idea of speed optimization is to balance fuel costs with flight time related costs (derived from maintenance, lease conditions, airline business model, crew costs, etc.) the way, that overall cost per mission/flight is minimized. Cost index (CI) was introduced for that purpose – simple formula combining fuel costs and time related costs -> CI allows to recalculate flight time to kgs of fuel and vice versa. Time related costs and fuel costs are typically airline proprietary information, and using CI formula allows to optimize flights w/o knowing the exact numbers – it is just the ratio.
Speed optimization techniques somehow differ depending on aircraft (A/C) capabilities. Most modern A/C have the capability to fly in so called ECON speed mode in cruise. This ensures that in every moment and environmental situation, the A/C is flying at optimum speed. Operations Control Centre (OCC) provides optimized CI for given route in OFP and CI value is entered into Flight Management System (FMS) by flight crew during initialization. In NAVsystem, it is possible to track fuel prices on different airports and time related costs for each A/C. This allows dynamic calculation of CI for each flight. NAVsystem support ECON speeds in OFP calculation so that fuel uplift is also optimized.
For A/C not supporting ECON speed mode, the overall optimization task is somehow more complicated. However, NAVsystem allows to easily calculate and compare overall cost per flight (considering both flight time and fuel burn costs) at different speeds. This allows to select optimum Mach speed (or other cruise mode) for given flight considering forecasted environmental data (wind & temperature), gross weight of the A/C and planned FL. In that case, flight crews should be aware of the fact, that speed is optimized for planned conditions – in case they are not able to fly in planned FL (conflicting traffic or generally ATC interventions) they should adjust speed accordingly. Determining optimum speed at +-2000ft around planned FL by OCC can be very helpful aid for flight crew to keep operational efficiency even in crowded airspace where probability that A/C will not be allowed to fly in planned FL cannot be neglected.
Situation also gets complicated when fuel tankering is extensively used. In those cases, fuel cost used when calculating CI for given flight should be the average cost of fuel – combining fuel cost at given airport with cost of tankered fuel including cost of carry.
Fuel tankering with accurate calculation of cost of carry is another efficiency feature of NAVsystem that significantly contributes to reduction of airline operational costs.