I can't give an answer but in case this point hasn't been thought of I'll add an extra piece of caution.(posted 8388 days ago)Xray dosage as with any exposure is cumulative. That means that if you fly out and have your films Xrayed and fly back with the same film (whether exposed or not), and so have it Xrayed again' it gets a second dose. So, if as we're told films to 1000 ISO are safe, for a double passage only a film to 500 ISO would be safe.
If you go on a multi-stage trip with a number of flights you can easily build up a significant cumulative dose which could bring even modestly rated emulsions into the danger zone.
The same build up of possible fog applys of course if you take film out and bring it back un-used (2 Xray passages), then take it out through an airport again on a second or even further trips! I mark film boxes/tubs to show which have been through airports and would make sure that they were used at home rather than taking then on further flights.
One further point, never pack films to go in the aircraft's luggage hold, Xray dosages of such luggage can I understand be much higher than for hand luggage.
Trevor