public ArrayList<Plane> SearchPlanesAvailable(Date d){

         ArrayList<Plane> foundPlanes = new ArrayList<Plane>();
        for(Plane p : planes.values()){
             boolean dontAdd = false;
             for (Flight f : flights.values()) {
                 if (d.getYear() == f.getDate().getYear() && d.getMonth() == f.getDate().getMonth() && d.getDay() == f.getDate().getDay() && f.getPlane() == p) {
                     dontAdd = true;
                 }
             }
             if (!dontAdd) {
                 foundPlanes.add(p);
             }
         }
        return foundPlanes;
    }