Maybe in the 70s, but that pretty much stopped with advent of metal detectors. And the hijackers had guns, not knives. Before 9/11 I carried a pocket knife on every flight I took.
Regardless, they’re doing it now, so I fail to see your point.
Before 9/11, my dad and I used to carry our fishing tackle boxes onto the plane because we didn't trust them to go through baggage handling. One time my dad brought a 10-inch fish gutting knife on a flight and didn't realize it until we got to our destination. Sailed right through the metal detectors and x-ray machines.
Maybe in the 70s, but that pretty much stopped with advent of metal detectors. And the hijackers had guns, not knives. Before 9/11 I carried a pocket knife on every flight I took.
Regardless, they’re doing it now, so I fail to see your point.