public async override Task Update <T>(T item)
 {
     if (typeof(T) == typeof(Aircraft))
     {
         InternalData.UpdateAircraft(item as Aircraft);
     }
     if (typeof(T) == typeof(Airfield))
     {
         InternalData.UpdateAirfield(item as Airfield);
     }
     if (typeof(T) == typeof(AcType))
     {
         InternalData.UpdateAcType(item as AcType);
     }
     if (typeof(T) == typeof(Flight))
     {
         InternalData.UpdateFlight(item as Flight);
     }
 }