Djswampy,
Your undertaker customer is winding you up. Corpses are not flown on passenger planes, only on cargo flights. Just for info, the airlines charge 150% the normal cargo rate to fly 'human remains' as they are called.
If they come in from a hot country they come in lead lined coffins to prevent the spread of disease and boy does that UP (get it ?) the cost of shipping them ! They are usually collected/delivered from/to the airline's cargo shed at night (in a black van) just for discretion.
About 60% of people die in their sleep, and are therefore 'collected' at night (these factors could explain why you don't see many black vans about in daylight hours!).
And finally NO I am not an undertaker, used to rally with one, and worked for a cargo airline.
Enjoy