Deductions & credits

Like you, my daughter also is a flight attendant for Delta.  I cannot seem to find anywhere in the tax code where it addresses  Time Away From Base as taxable or non-taxable.  In addition to this, there are two other pay codes listed in Box 14 with the abbreviations off OTH FRINGE AND WA PFML.   

 

tgfirst, can you advise if any of these are taxable or non-taxable?  If so, where can I find a provision or section of the code that slam-dunks this?

 

Much thanks!