Engine parts of Flight 93 were found far from the main debris field, a sign that it had been shot down.
According to Popular Mechanics, the engine was around 300 yards from the main crash site, and had travelled in the direction the plane was moving.
Jeff Reinbold, the National Park Service representative responsible for the Flight 93 National Memorial, confirms the direction and distance from the crash site to the basin: just over 300 yards south, which means the fan landed in the direction the jet was traveling. "It's not unusual for an engine to move or tumble across the ground," says Michael K. Hynes, an airline accident expert who investigated the crash of TWA Flight 800 out of New York City in 1996. "When you have very high velocities, 500 mph or more," Hynes says, "you are talking about 700 to 800 ft. per second. For something to hit the ground with that kind of energy, it would only take a few seconds to bounce up and travel 300 yards."
The Pittsburgh Pulp also got a quote from a weapons expert, regarding the debris you might expect to see if the Flight 93 engine had been hit by a missile.
Robert Sherman, a conventional weapons expert with the Federation of American Scientists who worked for the state department as former executive director of the Arms Control and Non-Proliferation Advisory Board, and also wrote extensively about F-16s and Sidewinder missiles, looked at the missile theories on flight93crash.com and deemed it "the usual paranoid crap."
"There was nothing there that gets me very worked up," he says. "Maybe [the plane] did break up. A crash is not a sanitary event. By definition, the uncontrolled impact of an airplane does strange things."
Sherman said that if a missile had hit Flight 93, there would have been more evidence. "If a Sidewinder had hit it, there would have been pieces of the fan or the fuselage in a larger area," he says. "If the engine breaks up, then the fan blades are going to come off like bullets. Pieces of the wing and fuselage would be all over the place."
So why was the engine found away from the main impact point? We can’t say for sure, but it’s happened before..
American Airlines flight 587, for instance, crashed in New York in November 2001 when its vertical stabilizer separated in flight. The NTSB report said...
"The engines, which also separated from the aircraft seconds before ground impact, were found several blocks from the wreckage site".
Of course we don’t know whether Flight 93’s engines “separated from the aircraft seconds before impact”, but this does show that distant engines don’t have to mean a plane was shot down. (Unless of course you want to contend that Flight 587 was shot down, although as both engines went astray this doesn’t look like a good explanation).