In flight/aircraft lingo, why is the word "souls" used for persons aboard?

Question

I hear "51 souls on board" etc.....what is the story behind why it is used?

Answer 1

Yeah, and if they're all wearing shoes, then that would mean that there are 102 SOLES aboard as well...

Answer 2

every person has a soul, never heard it myself.

Answer 3

The terminology was used for ships before airplanes.  

Soul speaks to the eternal worth and value of the life of each person on board, and the responsibility of those in command towards those

lives.

It implies a Christian world view.

Maggie