IIRC, the helo crashed after the SEALs it was carrying fast-roped on to the roof of one of the smaller buildings inside the complex. There are a lot of variables there and, no matter how many times the operation was rehearsed with scale models and the like, just a couple of inches could have caused the phenomenon that led to the 'copter's crash.
I've read several articles about the possible stealth technology apparent in the photos of the wrecked tail-boom and none of the sources have suggested it was silent or invisible. I didn't mean to inadvertently imply that this was so. Apparently, if one increases the number of rotors and reduces their size, the helicopter makes less noise. Also, the matte grey paint job is supposed to help confuse IR seekers on shoulder-launched SAMs. The angles of the tail-boom surface and the unusual rotor cap are supposed to reduce the copter's radar signature.
It's possible that the crew had trained in a "standard" spec-ops HH-60 and some little difference in the "stealth" version's performance could have contributed to the crash. Also keep in mind that the choppers had to fly over some very high mountains in order to get to Abbatabad. It's possible that engine strain or something to that effect contributed to the crash.
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