His plane crashed. He was flying in dense fog and he crashed. We don't know if the plane actually plunged, it might have skimmed or slid,but most likely crashed. Nobody really knows exactly what happened to him and his passengers, flying in a private plane while contemplating running for the Senate seat that Hillary Clinton had her eye on and was subsequently elected to.
The two most common causes of private plane crashes is running out of fuel or flying into conditions you are not trained for. Kennedy was flying a plane he was not totally trained on. He was not instrument certified. He was flying overwater on a warm and hazy day. He lost his reference and fell into a spin and that was it.
The problem he had was being VFR only qualified and flying in IFR conditions. He likely lost situational awareness and crashed. Knowing your limits is an integral part of any dangerous endeavor. JFK jr. obviously didn’t know his, or decided to ignore them.
CC
Yes, crashed into the ocean—
Spatial disorientation—
“ the inability to correctly interpret aircraft attitude, altitude or airspeed, in relation to the ground or point of reference”.
Plunging may indeed not be the
right word, but crashing into
the ocean due to spatial disorientation and his inexperience.
I do not think he was instrument rated. In poor visibility conditions, most likely succumbed to vertigo / disorientation and wound up in the ocean. But yes, you're right, we'll never know for certain.