How fast was Flight 77?

With some interest we could read the papers of Mr. Sozen about the Pentagon-Crash. As you might know, here in Europe there are some irritations because Mr. Sozen assumes a velocity of 800 ft/sec, which are about 850 km/h. The irritations resulted, because

1) some people say it is (for physically reasons) impossible that a Boeing 757-200 can have this velocity near the ground

2) other estimate a velocity of arround 500 - 600 km/h.

So I would be very pleased if somebody could give me a short comment to this problem. I could not find anything in the Forum or in the www about that.

Thanks a lot, Fanny

The WTC planes were traveling at full throttle (around 500 mph), but the Pentagon 757 was doing a descending spiral that limited its speed.

... but does anyone know why Mr. Sozen assumes 800 ft/sec, which are more than 500 mph?

Thanks again, Fanny

I've seen all sorts of estimates, between 250 and 600 mph (400-950 kph)

What I have never yet seen is a properly worked out justification of an estimate.

A Boeing under proper control would not usually fly so low so fast but because of what then should we pretend to know that the object was under any sort of control?

Often enough I have seen Concorde fly at similar speeds below 100O feet. Is hard to see therefore why it should not at all be possible for any other plane to do so.

The indicated airspeed (IAS) is no a direct measure of and aircraft's speed, it is an indicator of the pressures on the airframe normalized to sea level, IOW an indication of 200 knots means that the airframe is under the same pressure that would be felt at a speed of 200 knots at sea level. Because the air is thinner at cruising altitudes, most aircraft are designed to operate most efficiently at 250 knots IAS, which at 35,000 feet translates into a true airspeed (TAS) of ~450 knots (850 km/h). They become very ornery if you take them past 300 knots, and can only achieve such speeds in a dive. Most failsafe systems kick in the airbrakes and/or raise the nose if the speed approaches the aircraft's limitations, so to hit the Pentagon would have required either (1) flying in as though it were a normal approach to land or (2) making a sudden dive from a low altitude. In either case it's doubtful that it would have been going faster than about 200 knots (380 km/h).