internal bool IsWaitingLineEmpty(IWaitingLine waitingLine)
 {
     return(waitingLine.WaitingLine.IsEmpty);
 }
 internal bool IsExistInWaitingLine(IWaitingLine waitingLine, string flightNumber)
 {
     return(waitingLine.WaitingLine.Any(plane => plane.FlightNumber == flightNumber));
 }