Speaking as someone with knowledge of UPS export systems in the UK, I can clarify for you that at least here, all air export packages are x-ray screened twice, once at package centre and once upon export from the airport of choice. The systems for checking packages for air export in the UK have been extremely hot since 9/11. However even with all the systems inplace, as our friend in Louisville pointed out, one or two may get through..... I would like to assume the systems are the same globlally for international shipments. (US domestic airfreight is quite another matter.)