They had some footage of some cat launches gone wrong. In one an A-6
took
off the waist catapult of a carrier and started losing altitude almost
immediately. Then something really big fell off the plane, it started to
roll, and the pilots ejected at very low altitude.
Probably engine failure on the stroke. Possibly wrong weight setting on
the cat. The older catapults would use a given steam pressure to achieve
a particular end-speed for a particular gross weight. These would
malfunction on rare occasions. The newer cats use a rotary valve that
allows full pressure (600psi IIRC) for a particular duration and are just
about fool proof (unless its set for the wrong weight).
A fully-loaded A-6 didn't have very good single-engine fly away
capability. The "something" was probably all the underwing stores. Pilot
pushed the emergency jettison and the pylons were cleaned off.

If it's the event I'm thinking of, I heard an interview from the pilot. I
don't remember the cause of the problem, but it was either insufficient cat
stroke, or more likely, an engine problem (because I don't remember him
blaming the cat/crew). After the shot, the pilot noticed that they weren't
going anywhere (not a good thing), and tried to hack it. Folks on deck were
screaming to eject. The drop tanks were punched off late, then the B/N
ejected, then the pilot ejected. The pilot hit the water at almost a 90
degree angle but made it. The B/N didn't. The pilot went on to transition
to the F-14 after that cruise (one of the A-6s last).