One thing that has always bothered me about the Pentagon attack on 9/11 is this: while it would be relatively easy for a person with minimal training to fly an airliner on an essentially level flight path into a tall building, as well as quite simple to fly it into the ground: it would be extremely difficult for such a novice pilot to fly an airliner into the side of the Pentagon. The reason for this is called ground effect. As an airplane approaches the ground, specifically at about a distance of half a wingspan above the ground (which in a 757 would be approximately 65 to 75 feet AGL), ground effect provides a sudden increase in the lift of the plane. The Pentagon is only 5 stories, or approximately 50 to 60 feet tall, well within the ground effect of an airliner.
As the training received by the 9/11 hijackers (according to all reports after the incident) specifically concentrated on flying planes rather than the take-off & landing of planes, I question how they would have dealt with the unfamiliar ground effect phenomena, which would have significantly increased the lift of the plane just before it struck its target. The majority of flight training is focused on take-off and landing procedures due to the variable effects on the airplane as it leaves or approaches the ground.
Even if take off & landing training had been practiced on a light plane, such as a Cessna 172, there would be a huge practical difference in the ground effect compared to the much larger 757. Ground effect would occur within only 12 to 16 feet of the ground on the trainer aircraft, and there is another huge difference in the effect of cutting back on the throttles between a small prop plane & a turbofan powered jet airliner; considering both the massive differences in the inertia of the two different planes and the much higher airspeed of the 757.
This particular task of hitting the side of the Pentagon would be close to an aircraft landing on a carrier deck: a process requiring the most intensive training of any type of flying.
One possible way would be to fly into a beacon at the Pentagon providing Glideslope (GS) and Localizer (LOC) information. In this case all that would be required is flying a path provided by the instruments on the airplane. This type of training is available on home computer programs and can be easily and repeatedly practiced. This would also eliminate the flinch factor; by flying the instruments & not looking outside the airplane's windows the tendency to involuntary movement (closing the eyes & jerking the controls) just before the crash would be eliminated.
Norman Mineta, then Sec. of Transportation, who was with Vice-President Cheney on 9/11 in the Presidential Emergency Operating Center, reported to the 9/11 Commission:
"There was a young man who had come in and said to the vice president, 'The plane is 50 miles out. The plane is 30 miles out.' And when it got down to, 'The plane is 10 miles out,' the young man also said to the vice president, 'Do the orders still stand?' And the vice president turned and whipped his neck around and said, 'Of course the orders still stand. Have you heard anything to the contrary?' Well, at the time I didn't know what all that meant."
GS & LOC are part of the ILS (Instrument Landing System); another part of which is called DME (Distance Measuring Equipment) which provides the distance from the location of the DME transmitter to the airplane's transponder (it also provides the speed over the ground of the airplane). This would provide a simple and realtime method to determine how far away A.A. Flight 77 was from the Pentagon. That information was obviously & immediately available. It seems unlikely that any other sources (such as Civil or Military Air Traffic Controllers or ATCs) could provide this data in this timely a fashion. Since the Pentagon is not an airport it would require at least some calculation (trigonometry) to extrapolate the distance of A.A. Flight 77 from the Pentagon as compared to location of the ATCs instruments. Since the plane was traveling at least 5 or 6 miles per minute, it seems difficult to provide such realtime data from an external site.
While it would not be impossible for novice pilots to fly an airliner into the side of the Pentagon, it would be very difficult to have so precisely hit their target without some external guidance. Such guidance could also explain Sec. Mineta's observations and (ominously) V.P. Cheney's remarks. Beacons on the WTC could also explain the accuracy with which A.A. Flight 11 and U.A. Flight 175 hit their targets: an easier but still difficult task for novice pilots.