I was a manager before I got to Honeywell, but not here. Let's face it, some people need informal PIPs. But formal PIPs are only necessary to avoid unemployment payments or discrimination law suits in employment at will states like AZ if the employee doesn't shape up. But the use of impossible PIPs at Aero in AZ, at least in ISC and GSI, as an excuse to fire someone dates back over 10 years. I saw those PIPs before those age protected people were walked out later.
My point is this, almost everyone is a "protected species" based on age, s-x, race, handicap, medical issues, etc. If you get put on an impossible PIP and fall into one of those categories (sorry, you white guys under 40), immediately file a complaint with the EEOC while you are still employed. You will be protected for as long as it takes for the EEOC system takes to decide what to do, and you get the psychic benefit of knowing that management gets closely questioned about what is going on.
But don't wait until you are unemployed since the clock is ticking on your time at that point, not theirs.