http://www.straightdope.com/columns/051230.html
The big problem not mentioned is if the cargo is kept in either an unpressurized or unheated hold of a cargo plane. You might arrive at your destination, but be dead.
That’s true. However, there’s a travel UL that says you can often get a dirt-cheap fare in a short row of seats aboard a FedEx or UPS jet in the middle of the night. On a passenger jet, the luggage hold is unpressurized, but on a cargo jet, the cargo rides in the main cabin. Would it be pressurized?