Grenada etc.
Tcabot,
Not sure I recall the accidents in their proper chronological order, but two Army accidents from that exact period stuck in my mind, and one that occurred at Sikorsky.
One occurred at Hooper stage field within the Ft Rucker complex, with all fatally injured, and was caused by a main rotor servo failure. This failure resulted from "hydrogen embrittlement " of the main rotor servo material, a phenomena which markedly reduced the fatigue strength of the servo. Main rotor servos had severe ballistic survivability requirements and Hydraulic Research Co had used a mfg process which led to the embrittlement proble.
Another occurred at Ft Bragg, where two A models were flying low level, next to one another, with the infantry troops waving at one another, when one simply nosed over and went in upside down, with all fatally injured. They were going pretty fast, so the rotor, control system etc, wound up all over the place and some of it buried fairly deep. Of course the media and rumor mill immediately pronounced the cause as the stabilator failing full down. That investigation took six months before we found the cause. Maintenance records were available, and we knew the control mixing unit had been worked on, but subsequent flying had produced no flight gripes. It took some months before we found all the parts, and found a bolt in the longitudinal mixer control missing a nut, then found the non-safetied nut with damage marks which fit some curious indentation marks in the longitudinal control limiter within the mixer.
Think I've mentioned this previously, but the only stabilator caused accident was the test aircraft at SA, which was caused by two separate human errors. But scuttlebutt can be a powerful influence, and it turned out that we at SA learned, after the Grenada assault, that with the Ft Bragg units, they were putting the stabilator in manual, zero degrees incidence, when they started in on the approach, ensuring that the pitch attitude would be far higher than normal when the main rotor down wash impinged upon the tail. BTW, did I ever mention that when I first got a close look at an AH-64, and looked at their stabilator installation, the actuator part number began with: 70-xxx-xxx, I.e., it was a UH-60 part! This was awhile ago, of course.
Thanks,
John Dixson