public async override Task Delete <T>(T item)
 {
     if (item.id == 0)
     {
         throw new Exception();
     }
     if (typeof(T) == typeof(Aircraft))
     {
         InternalData.DeleteAircraft(InternalData.Lookups.Aircraft.FirstOrDefault(x => x.id == item.id));
     }
     if (typeof(T) == typeof(Airfield))
     {
         InternalData.DeleteAirfield(InternalData.Lookups.Airfields.FirstOrDefault(x => x.id == item.id));
     }
     if (typeof(T) == typeof(AcType))
     {
         InternalData.DeleteAcType(InternalData.Lookups.AcTypes.FirstOrDefault(x => x.id == item.id));
     }
     if (typeof(T) == typeof(Flight))
     {
         InternalData.DeleteFlight(InternalData.Flights.FirstOrDefault(x => x.id == item.id));
     }
 }