private void BtnFlight_Click(object sender, RoutedEventArgs e)
        {
            Aircompany selectedCompany = (Aircompany)DGAircompany.SelectedItem;

            for (int i = 0; i < Data.Instance.Flights.Count; i++)
            {
                if (selectedCompany.Id.Equals(i))
                {
                    FlightsWindow ef = new FlightsWindow();
                    ef.ShowDialog();
                }
            }
        }
        private void BtnFlights_Click(object sender, RoutedEventArgs e)
        {
            FlightsWindow fw = new FlightsWindow();

            fw.ShowDialog();;
        }