Caveat first: I'm not bothering to read the complaint. Or to go digging into Nevada case law.
Employment at will as a matter of state law, even in those states which hold it within the realm of the highest and most worthy of legal principles, is not a head-to-toes defense. As a prior poster impliedly noted, violation of any applicable employment-related law in effect "trumps" the at-will doctrine. More importantly for this matter, violation of a public policy (yes, that phrase is tricky to define) also is grounds to set the at-will doctrine aside. Thus, IF Nevada law indeed is the applicable law and IF it recognizes aviation safety rules as such a public policy, for example in the form of FAA regulations, the at-will doctrine will see lots of play in lots of ink spilled by defense lawyers, perhaps, but technically it is not a winning defense (that is, IF the pilot can show his actions consistent with the applicable safety rules).
Besides, the pilot retained a former highly-ranked FAA attorney. As a defense counsel, this would give me pause in assuring my client that much money will have to be spent (whether directly or through an insurer) on motion practice and discovery, prior to having to fish or cut bait ("settle", for the non-lawyers reading).
As for the wisdom of the pilot's actions, I'm deferring to the people who know what they're talking about . . .