[cynwoody]

There is only one problem with the concept of airliners being used as a missiles. Their engines compress air. Due to air density close to the ground, when they fly at very low altitude they can not fly faster than 250 knots. The only way to gain high speed at low altitude is to nosedive them from cruising speed at high altitude, but they would probably disintegrate mid-air. So airliners as missiles is is mostly Tom Clancy/F-X territory.

Not true. United 175 was doing 469 knots when it hit WTC 2, about 87 knots faster than AA 11 hit WTC 1. That's according to NIST (see here (18mb PDF), page 38). Flight 175 made a rapid descent after it was hijacked (about 5000 feet/min — faster than Germanwings), but there was no "nosedive". It was in more or less level flight when it hit.

https://www.youtube.com/watch?v=K4vvVyKyy0k

[DTA]

United 175 was Boeing 767-200.

According to published data top speed of B767-200 is Mach 0.86 (493 knots, 567 mph, 913 km/h at 35,000 ft cruise altitude.Typical Cruise Speed at 35,000 feet is Mach 0.80 (530 mph, 851 kph)

No doubt Boeing 76-200 can fly 469 knots at 35,000 ft, but can it fly at 469 knots at 1,000ft (approx. height of WTC2 impact)? That is question for Pratt & Whitney. Many pilots say it can not.