Interesting - I’m trying to dig that out of my memory, and I can only think that Jack may have mentioned it during a radio interview. It’s on my follow-up list of stuff that’s going to drive me crazy.
I would think that if the smaller plane (a Cherokee 6 at gross weight [3400 lbs.] weighs about 600 pounds less than a Ford Explorer, as a comparison. It has just a 33’ wingspan and is just over 27 feet long. Not that big. With the transponder off, its physical radar signature would probably blend into the 747’s radar signature, which would be the prominent radar return.
I wish my friend were still here - he was also a radar expert witness and could answer that question in a hot second. Plus, he was one of the sharpest, funniest, and most big-hearted people I ever knew.
Just a couple of thoughts as possibilities.
I find it hard to believe that a Piper Cherokee could do a 13,000+ altitude intercept on a 747 climbing out at 300+ knots/1000 feet per minute.
Well outside it’s performance envelope.