The eyewitness in question is none other than Susan Mcelwain
She claims she saw a UAV type aircraft performing some incredible acrobatic feats. The technology described appears to be far superior to that of a Predator or Global Hawk. Some people have backed up her claims with evidence of some new police and military UAV's that share features and are able to match the performance of the craft she saw that day.
What are the views on her testimony? What about the countless video interviews of her accounts of that day?
There's not much to tell. Ms. McElwaine has extremely little knowledge of aircraft, as evinced by her use of nonstandard terminology, such as "spoilers" and "fins." She also describes what is nearly impossible, i.e. a jet aircraft passing within 100 feet of the ground, yet being almost silent. Her value as a witness is quite limited. (ETA: "Spoilers" are present on modern aircraft, but they aren't what she thinks they are. They are control surfaces on the upper wing that "spoil" aircraft lift, allowing descent without a great increase in speed.)
The most plausible explanation, from my perspective, is that the aircraft she described was the well-known white Falcon 20 business jet that
was in the area, and
was asked by Air Traffic Control to survey the area looking for the crash site. I believe they were flying at an altitude of only a few thousand feet, which would plausibly match the apparent size and speed of the object Ms. McElwaine described.
If the aircraft was not the Falcon 20, whatever it was went unnoticed by them and by Air Traffic Control. A stealth aircraft? Or flying at extremely low altitude? Ms. McElwaine seems to imply the latter.
However, this is not possible. If the aircraft was truly as low as she says, then it had to be very small as well, so small that it cannot have carried a pilot. Regarding UAVs, there are no UAVs that can operate so close to the ground. I've
commented before on why UAV technology is inadequate to create "drone planes" that hit the World Trade Center, and the mission called for in this case -- flying nap-of-the-earth in rural Pennsylvania -- would be far more challenging.
The reason why this can't be done remotely is quite simple. At an altitude of, say, 100 feet, and speed of 250 knots, the time required to close the control loop without hitting ground obstacles is on the order of 200 milliseconds to execute the full cycle. This is at about the limit of human performance. If you add radio control and comm latency, this is totally impossible.
Similarly, there are no on-board autonomy systems with that level of performance. All current UAVs that are not remotely piloted
will not let you fly that low. Global Hawk, for instance, only passes through those altitudes during takeoff and landing, and only after it has taken a radar image of the ground so that it knows there are no obstacles along its intended flightpath. Otherwise, it would not even sense the obstacles.
The only UAVs that can possibly operate at such low altitude are those which are both small and
slow. There are some autonomous helicopter efforts at NASA Ames, for instance, but they are far from mature, and Ms. McElwaine wasn't describing a whirlybird. There are also several lightweight, hand-thrown and similar surveillance platforms, but these rarely exceed 100 knots, and many are slower still. I fail to see what possible threat such a small and impotent UAV could have presented to a jetliner. Such a UAV would not have a hope of intercepting or even tracking a 500+ knot capable large transport. It couldn't even get out of the way.
The fantasy UAV story strikes me as yet another unfounded UFO story, and nothing more.
