[Boundless]

> I remember during testing an F22 having a strange
> instability on takeoff where it went up and down
> in sort of a sine wave before crashing.

That was the YF-22 prototype, April 25, 1992.

PIO (Pilot-Induced Oscillation) due to an unfortunate
coincidence of the computer flight control laws and
the reactions of the pilot. Not at all uncommon in
early flights of fly-by-wire a/c.

PIO was my first thought when I saw today's news, but
chances are it's some other problem. This is why test
flights are test flights.

[TalonDJ]

From what I know that YF-22 crash was because the pilot failed to disable the thrust-vectoring when taking off. The vectoring was not meant for takeoff use and that caused the PIO. If such s system is still used (the pilot has to be sure it is off) then the same thing could have happened. That is pure speculation though. They probably changed the system. That is an incredibly complex aircraft so a great many things could have gone wrong. My money would be on a software problem.