previous one are still propagating through the fuel system however a short holding time for discrete ratios attempted may be applied in order to help delineate between each condition to be sampled the required duration of holding time may be predetermined based at least in part on the known contrail lead time tolerance and or any recorded variation in contrail lead time over the course of a single flight between flights or between different aircraft of the same design in any event it is envisaged that the holding time will be significantly smaller in magnitude than the contrail lead time for a continuous sweep the rate of change of the fuel blend may be tailored to avoid the need for a holding time or else a shortened holding time may be applied at discrete intervals in any of the search examples described above a first step of the search may comprise a determination of a list of points i e fuel blend ratios to be explored within the search space this can be done by evenly distributing a given number of points across an n dimensional space another although typically less efficient for two or higher search dimensions approach would simply.