A shomer from my local Chevra Kadisha explained to me that a dead body needs to be constantly watched and never left alone until burial. He also explained that about every 20 minutes, they say Tehillim.
With this concept, I am curious as to what occurs when the body is shipped on a flight from U.S. to Israel (or any flight). In my case, I was an onen on the flight, and, of course, the body was handled as cargo and placed in the luggage / cargo area. I wasn't watching the body; if anything, I was asleep most of the flight.
During the loading and unloading process, (well, considering burial was in Israel, perhaps just loading ;-) Gentiles were handling the body (I assume that they can't be Shomrim), so there were no Shomrim at that time.
Does the body actually require constant guarding or are exceptions allowed such as for the circumstances that I described?