It’s not a case of an unsafe plane. It’s a case of a flight crew flying into some of the most intense thunderstorms in the world and not knowing how to deal with the violent winds inside these thunderstorms.
One does NOT knowingly fly into a thunderstorm period. If you do you will at the very least regret it, and bend something and at the worst you have this thread or one like it.
Back when I was flying with the USMC, a job notice circulated around the squadron. A Midwestern university was seeking "qualified T-28 pilots to fly a T-28 for thunderstorm penetration research". This generated a lot of cynical laughs.
Any "qualified T-28 pilot" knew that the envelope of the T-28 had been reduced from 6g to 4.5g due to the age of the airframes. 4.5g is not a lot, yet in this case, there was the danger of ripping the wings off.
Any qualified pilot also called large thunderstorms "Gators" because they can 'chew you up and spit you out'.
Finally, most of us had read the account of Lt Colonel William Rankin, USMC.
The Man Who Rode the Thunder (Hardcover) June, 1960 by William H. Rankin .