Why did the FAA have the ATC towers in Cleveland, Johnstown, and Pittsburgh evacuated when Flight 93 was in the area, but did NOT have the ATC towers at Dulles and Reagan International evacaute when FL 77 was approaching?

Anybody know if there is an official explanation for this?

My first thought is that the FAA did NOT want the controllers in Cleveland, Pittsburgh, and Johnstown to see something, but DID want the controllers in Washington to see something.

What's even more puzzling about the control tower evacuations is that nobody can pin down who specifically ordered the evacuations. According to the Johnstown controllers, they said "somebody" from the Cleveland airport called them to tell them to evacuate their control tower because Flight 93 was heading their way. Only problem with this is that the people in Cleveland told the controllers in Johnstown that Flight 93 was heading towards Johnstown from the south, when in fact, according to the official story, Flight 93 would have been approaching Johnstown from the north.

Even more bizarre is that the control towers were ordered evacuated AFTER the FAA issued an order that all planes in the air were to land immediately at the nearest airport. So how would the FAA expect the planes near Pittsburgh to land at the Pittsburgh airport if the airport's control tower was evacuated? This entire sequence makes no sense.

In fact, what's worse about this that after the control towers were evacuated, NORAD asked the FAA to give them a location for Flight 93. The FAA told NORAD that Flight 93 was lost from radar. Well no kidding! The controllers tracking Flight 93 were told to evacuate their stations.

So one can only wonder why the FAA told air traffic controllers at three airports along the flight path of Flight 93 to evacuate the control towers on 9/11. If Flight 93 would have needed to make an emergency landing in Pittsburgh, the control towers would have been empty per the orders of the FAA. And because of this order to evacuate the control towers on 9/11, nobody will ever know what the controllers would have seen had they remained at their stations.