The rule that catches people out
TSA officers are not permitted to open a container holding cremated remains, even at the passenger’s request. That means the container has to be screenable as it is. A dense stone, solid brass or lead-lined urn will not resolve on X-ray, and the officer’s only available answer is that it cannot pass.
This happens at the checkpoint, with a queue behind you, on the day of a funeral. It is worth ten minutes of preparation.
What to carry it in
Wood, plastic, cardboard or thin non-lead metal all screen cleanly. Many crematories supply a temporary transport container for exactly this purpose, often at no charge, and the decorative urn travels separately in checked baggage or ships ahead.
Carry-on is generally the safer choice for the remains themselves. Checked baggage is not prohibited, but a lost bag is a different kind of loss here.
Paperwork worth having
Carry a certified copy of the death certificate and the crematory’s certificate of cremation. Neither is universally demanded domestically, but both end a conversation quickly if one starts, and international travel and some airlines do require them.
For an international destination, check the receiving country’s consulate as well as the airline. Requirements vary widely and the airline’s rules are not the whole picture.
Tell the airline in advance
Airline policies on cremated remains differ, and a few require advance notification or restrict them to carry-on. Ring the airline rather than relying on a general summary — including this one, which is accurate today and may not be next year.