Steve McQueen's father, William McQueen (1907–1958), might have been a stunt pilot for a barnstorming flying circus, its possible, but it's certain he was in the merchant marines

The Life Steve McQueen By Dwight Jon Zimmerman

I bring up that it's possible, because once someone wrote that, EVERYTHING on line about him repeats it. Well, what if they made it up because it was sensational? Then that lie is spread, and the truth is never known

https://medium.com/@jeremylr/how-a-military-brat-got-hooked-on-the-razor-sharp-mystique-of-quintessential-hollywood-outsider-2cc632f95bc1

I was able to determine what his occupation was — Merchant Marine, not a barnstorming pilot — his last known address — Long Beach, California — the cause of death — cirrhosis of the liver — and his social security number.

The social security number allowed me access to his military file, which contained his photos, his various tours of duty, and where he traveled in the years after he left Jullian and Steve. And then it made sense how William was able to stay under the radar and evade Steve all those years — he was constantly out to sea.

both of Steve's parents were dead by the time he turned 35

https://en.wikipedia.org/wiki/Steve_McQueen

Here's a photo of Steve's grandfather, Lewis

https://www.ancestry.com/family-tree/person/tree/57614136/person/42024180696/gallery