Look at the history.
Star Simpson, a sophomore at the Massachusetts Institute of Technology was taken into custody after with a circuit board measuring roughly 2 inches by 6 inches, with protruding wires, lights and a nine-volt battery on the back of a black, hooded sweatshirt. When arrested she said it was an art project.
Five Muslims on a plane take positions much like the 9/11 hijackers.
Five Muslims asked for seat belt extenders, a potential weapon, which none of them needed.
There have been hundreds of attempts to get items on a plane that could help in a hijacking by people who one would not be considered a terrorist.
What is happening here? This is a multi-front movement to enable terrorists to once again take the skies to harm America. I am sure that at the minimum terrorists leaders are watching these events, looking for weaknesses in the security and they may even be orchestrating them.
Allow me to give you an example. In the spring of 1942 the American intelligence services had broken the Japanese Naval Code and were reading the messages to and from the Japanese fleets. But there were some words, particularly names of people and places that were unknown. The messages showed an attack was coming but the name of the place was unknown. Intelligence officers were sure it was either Wake or Midway but there was no way from the messages or fleet movements to tell for sure.
Midway island had an undersea cable to it, a secure communication line. A message was sent to the Midway Commander to send out a message, in the clear, i.e. not encrypted, saying the island's desalination plant was broken. The commander did as directed. Within a day a message from Japanese Naval Headquarters to the fleet advised them that an American base with that name would likely be short on fresh water! The Japanese just told us where the attack would come! That information enabled better disposition of forces and search efforts - two things that contributed greatly to the victory at Midway. Seemingly innocent acts can break security.
For a terrorist attack to be successful several things have to come in focus at the same time. They have to get the people where they need to be, with the tools (weapons) they need and they need to not have anyone notice or get concerned until it is too late. If someone had gotten really curious about the men on these flights on 9/11 before they boarded, all of the attacks may have failed. Let's face it, on 9/11 two of the attacks were successful resulting in over 2500 deaths and the destruction of two buildings worth billions of dollars. And the impact on our society was terrible.
You will say, "They hit the pentagon and all four planes crashed." True. But two of the attacks failed, one miserably. And we need to learn why they failed. The planes that hit the towers took over 1200 lives each and resulted in billions of dollars of damage. Flight 77 hit the pentagon and the loss of life was 184, far below the number at New York. Pan Am 103 at Lockerbie resulted in 270 deaths and that took far less planning and resources to accomplish.
The Flight 77 crash, although terrible, was certainly not the significant event it was hoped to be. They damaged the Pentagon, but they did not destroy even a significant portion of it. Part of that failure was due to approach, part to the inexperience of the pilot. Hitting a tall building, compared to a low one is relatively easy yet one plane in New York nearly missed the one tower. These guys were marginally able to keep a plane in the air.
To hit a tall building you can stay well above ground objects and line up on the target. To hit a relatively low building the pilot has to fly a profile that enables him to stay above ground objects and then still be or dive low enough to hit the building. The pilot of Flight 77 actually hit the ground and lost some momentum before hitting the Pentagon. This certainly reduced the damage and loss of life.
A solid hit or better yet a "dive bomber" approach into the building from above would have almost certainly spread the fuel more and been far more "productive" to the Muslim cause in damage and loss of life. But requesting training in that maneuver would almost certainly raised an alarm. Why would a commercial pilot trainee want to learn how to crash a plane into an object on the ground? That would almost certainly have raised a red flag.
But some of the other things about the hijackers raised at least yellow flags and they were ignored, even ones noted as unusual by the flight instructors. If a flight instructor had said to me in 2000, "I have a student who seems uninterested in landings and takeoffs," I would have had serious questions. Even if I could rationalize out not wanting to learn takeoffs, not wanting to learn landing makes no sense. Once you are in the air, someone has to land the plane.