The story...

How could such precision attacks have been carried out by a bunch of flight school dropouts? It's just not possible.

Our take...

Spend some time reading about 9/11 and you'll come up against this argument a lot. In fact, as we write, if you Google for "flight school dropouts" then 9 out of the top 10 hits relate to 9/11. Nila Sagadevan uses the following quotes by way of illustration:

Not one of the hijackers was deemed fit to perform this most elementary exercise by himself, in fact, here is what their flight instructors had to say about the aptitude of these budding aviators:

Mohammed Atta: "His attention span was zero."

Khalid Al-Mihdhar: "We didn't kick him out, but he didn't live up to our standards."

Marwan Al-Shehhi: "He was dropped because of his limited English and incompetence at the controls."

Salem Al-Hazmi: "We advised him to quit after two lessons."

Hani Hanjour: "His English was horrible, and his mechanical skills were even worse. It was like he had hardly even ever driven a car. I'm still to this day amazed that he could have flown into the Pentagon. He could not fly at all."
http://www.venusproject.com/ethics_in_action/911_Impossible_Flying_757.html

Looks like a compelling case, right? But as usual, it pays to find out more about where these quotes have come from.

The comment about Atta, for instance, dates back to October of 2000. He undertook months more training after this, and qualified for a commercial licence, so it’s perhaps unreasonable to use this old quote as a summary of his flying on 9/11.

Jones Aviation flying instructor Ivan Chirivella told investigators that Atta, 33 and al-Shehhi, 23 came across from Huffman Aviation hoping to improve their sloppy skills. Chirivella flew with Atta and al-Shehhi four hours almost every morning from Sept. to October 2000. It didn’t work out. According to the New York Times, Atta never looked at his instructor. His attention span was zero. Al-Shehhi fared no better. “After some harsh words,” both fledgling militants moved on.
http://www.willthomas.net/911/911_Commission_Hearing.htm

Googling for the Al-Shehhi quote returns only references to the Sagadevan article, which doesn’t explain where it came from originally. 

Khalid Al-Midhar was not one of the pilots according to the official account, neither was Salem Al-Hazmi, so any assessment of their abilities seems irrelevant.

Some of the quote about Hanjour is correct (“I'm still to this day amazed that he could have flown into the Pentagon. He could not fly at all”). This comes from a “former employee” at JetTech, a flying school Hanjour attended in January and February of 2001 The rest of the quote didn’t originally refer to Hanjour, though: it’s somehow been assembled from a comment about Al-Mihdhar and Al-Hazmi:

Alleged suicide pilots Nawaq al-Hazmi and Khaid al-Mihdhar briefly attended a San Diego fight school the previous spring, where they also washed out because of their limited English and incompetence at the controls. After just two flying lessons, their shaken instructors said “no more,” and advised al-Hazmi and al-Mihdhar to quit. “Their English was horrible, and their mechanical skills were even worse,” one instructor told the Washington Post. “It was like they had hardly even ever driven a car.
http://www.willthomas.net/911/911_Commission_Hearing.htm

To see whether old quotes are really relevant, it might be worth considering the training the pilots received. Take Atta and Shehhi, for instance, as reported in the 9/11 Commission Report.

Atta started flight instruction at Huffman Aviation in Venice, Florida, and both Atta and Shehhi subsequently enrolled in the Accelerated Pilot Program at that school. By the end of July, both of them took solo flights, and by mid-August they passed the private pilot airman test
http://www.faqs.org/docs/911/911Report-241.html

A reasonable start, although there were problems later.

In mid-September,Atta and Shehhi applied to change their immigration status from tourist to student, stating their intention to study at Huffman until September 1, 2001. In late September, they decided to enroll at Jones Aviation in Sarasota, Florida, about 20 miles north of Venice. According to the instructor at Jones, the two were aggressive, rude, and sometimes even fought with him to take over the controls during their training flights. In early October, they took the Stage I exam for instruments rating at Jones Aviation and failed. Very upset, they said they were in a hurry because jobs awaited them at home. Atta and Shehhi then returned to Huffman.
http://www.faqs.org/docs/911/911Report-241.html

Jarrah was making progress in the meantime.

Jarrah obtained a single-engine private pilot certificate in early August.
http://www.faqs.org/docs/911/911Report-241.html

And Atta and Shehhi had more success later in 2000, while Jarrah moved to simulator training.

Atta and Shehhi finished up at Huffman and earned their instrument certificates from the FAA in November. In mid-December 2000, they passed their commercial pilot tests and received their licenses.They then began training to fly large jets on a flight simulator. At about the same time, Jarrah began simulator training, also in Florida but at a different center. By the end of 2000, less than six months after their arrival, the three pilots on the East Coast were simulating flights on large jets.
http://www.faqs.org/docs/911/911Report-244.html

Not perfect or the best pilots, then, but maybe the term "flight school dropout" is a little misleading here.

Of course the more realistic target for these claims is Hani Hanjour. Here's one comment.

Alleged flight 77 (Pentagon) pilot Hani Hanjour had a history of great difficulties in his efforts to learn to fly. As late as Aug. 2001, he was unable to demonstrate enough piloting skills to rent a Cessna 172...

Certainly there is no evidence that Hanjour ever had any sort of practice flying commercial jetliners or any jet-propelled aircraft.
http://www.911-strike.com/remote_skills.htm

The site quotes this NewsDay article:

...when Baxter and fellow instructor Ben Conner took the slender, soft-spoken Hanjour on three test runs during the second week of August, they found he had trouble controlling and landing the single-engine Cessna 172. Even though Hanjour showed a federal pilot's license and a log book cataloging 600 hours of flying experience, chief flight instructor Marcel Bernard declined to rent him a plane without more lessons.
Source

Even the 9/11 Commission Report joins in:

For his flight training in Arizona with his two friends, see ibid. (Feb. 24, 2000, entry citing 265A-NY-280530-IN, serial 4468). Hanjour initially was nervous if not fearful in flight training. FBI letterhead memorandum, investigation of Lotfi Raissi, Jan. 4, 2004, p. 11. His instructor described him as a terrible pilot. FBI letterhead memorandum, interview of James McRae, Sept. 17, 2001.
http://www.faqs.org/docs/911/911Report-537.html

Read these quotes alone, though, and you might be mislead. The first seems to suggest that he hadn't learned to fly by August 2001, however he'd actually obtained both a private pilot and commercial license some time earlier.

In 1996, Hanjour returned to the United States to pursue flight training,after being rejected by a Saudi flight school. He checked out flight schools in Florida, California, and Arizona; and he briefly started at a couple of them before returning to Saudi Arabia. In 1997, he returned to Florida and then, along with two friends, went back to Arizona and began his flight training there in earnest. After about three months, Hanjour was able to obtain his private pilot's license. Several more months of training yielded him a commercial pilot certificate, issued by the Federal Aviation Administration (FAA) in April 1999.
http://www.faqs.org/docs/911/911Report-242.html
http://www.faqs.org/docs/911/911Report-243.html

Settling in Mesa, Hanjour began refresher training at his old school,Arizona Aviation. He wanted to train on multi-engine planes, but had difficulties because his English was not good enough.The instructor advised him to discontinue but Hanjour said he could not go home without completing the training. In early 2001, he started training on a Boeing 737 simulator at Pan Am International Flight Academy in Mesa.An instructor there found his work well below standard and discouraged him from continuing.Again, Hanjour persevered; he completed the initial training by the end of March 2001.
http://www.faqs.org/docs/911/911Report-243.html
http://www.faqs.org/docs/911/911Report-244.html

Hanjour continued his training with Jarrah throughout at least some of the summer. Again, there were problems in both cases, but they persisted.

Jarrah and Hanjour also received additional training and practice flights in the early summer.A few days before departing on his cross-country test flight, Jarrah flew from Fort Lauderdale to Philadelphia, where he trained at Hortman Aviation and asked to fly the Hudson Corridor, a low-altitude "hallway" along the Hudson River that passes New York landmarks like the World Trade Center. Heavy traffic in the area can make the corridor a dangerous route for an inexperienced pilot. Because Hortman deemed Jarrah unfit to fly solo, he could fly this route only with an instructor.

Hanjour, too, requested to fly the Hudson Corridor about this same time,at Air Fleet Training Systems in Teterboro, New Jersey, where he started receiving ground instruction soon after settling in the area with Hazmi. Hanjour flew the Hudson Corridor, but his instructor declined a second request because of what he considered Hanjour's poor piloting skills. Shortly thereafter, Hanjour switched to Caldwell Flight Academy in Fairfield, New Jersey, where he rented small aircraft on several occasions during June and July. In one such instance on July 20, Hanjour--likely accompanied by Hazmi--rented a plane from Caldwell and took a practice flight from Fairfield to Gaithersburg, Maryland, a route that would have allowed them to fly near Washington, D.C. Other evidence suggests that Hanjour may even have returned to Arizona for flight simulator training earlier in June.
http://www.faqs.org/docs/911/911Report-259.html

Even Hanjour wasn't exactly a "flight school dropout", then. He had a private and commercial pilots licence, and a not insignificant amount of flying experience, including some simulator work (although on 737's). There are definitely plenty of scathing quotes regarding his skills:

Chevrette said she contacted Anthony again when Hanjour began ground training for Boeing 737 jetliners and it became clear he didn't have the skills for the commercial pilot's license.

"I don't truly believe he should have had it and I questioned that," she said.
http://www.cbsnews.com/stories/2002/05/10/attack/main508656.shtml

However, an early instructor isn't quite so damning:

FBI agents have questioned and administered a lie detector test to one of Hanjour's instructors in Arizona who was an Arab American and had signed off on Hanjour's flight instruction credentials before he got his pilot's license.

That instructor said he told agents that Hanjour was "a very average pilot, maybe struggling a little bit." The instructor added, "Maybe his English wasn't very good."
http://www.cbsnews.com/stories/2002/05/10/attack/main508656.shtml

One 9/11 Commission footnote (to Chapter 7) is relatively positive.

170. FBI report, "Summary of Penttbom Investigation," Feb. 29, 2004, pp. 52­57. Hanjour successfully conducted a challenging certification flight supervised by an instructor at Congressional Air Charters of Gaithersburg, Maryland, landing at a small airport with a difficult approach.The instructor thought Hanjour may have had training from a military pilot because he used a terrain recognition system for navigation. Eddie Shalev interview (Apr.9, 2004).

And as Marcel Bernard pointed out, the hijackers wouldn't have required all the skills of a regular pilot:

"Despite Hanjour's poor reviews, he did have some ability as a pilot, said Bernard of Freeway Airport. "There's no doubt in my mind that once that [hijacked jet] got going, he could have pointed that plane at a building and hit it," he said"
http://www.pentagonresearch.com/Newsday_com.htm

People will still say that the Pentagon attack was too difficult for Hanjour to have pulled off (see here), however other debunking articles quote pilots saying that isn’t the case (see here). Salon produced a recent example of the second type, written by an airline pilot (below):

As I've explained in at least one prior column, Hani Hanjour's flying was hardly the show-quality demonstration often described. It was exceptional only in its recklessness. If anything, his loops and turns and spirals above the nation's capital revealed him to be exactly the shitty pilot he by all accounts was. To hit the Pentagon squarely he needed only a bit of luck, and he got it, possibly with help from the 757's autopilot. Striking a stationary object -- even a large one like the Pentagon -- at high speed and from a steep angle is very difficult. To make the job easier, he came in obliquely, tearing down light poles as he roared across the Pentagon's lawn.

It's true there's only a vestigial similarity between the cockpit of a light trainer and the flight deck of a Boeing. To put it mildly, the attackers, as private pilots, were completely out of their league. However, they were not setting out to perform single-engine missed approaches or Category 3 instrument landings with a failed hydraulic system. For good measure, at least two of the terrorist pilots had rented simulator time in jet aircraft, but striking the Pentagon, or navigating along the Hudson River to Manhattan on a cloudless morning, with the sole intention of steering head-on into a building, did not require a mastery of airmanship. The perpetrators had purchased manuals and videos describing the flight management systems of the 757/767, and as any desktop simulator enthusiast will tell you, elementary operation of the planes' navigational units and autopilots is chiefly an exercise in data programming. You can learn it at home. You won't be good, but you'll be good enough.

"They'd done their homework and they had what they needed," says a United Airlines pilot (name withheld on request), who has flown every model of Boeing from the 737 up. "Rudimentary knowledge and fearlessness."

"As everyone saw, their flying was sloppy and aggressive," says Michael (last name withheld), a pilot with several thousand hours in 757s and 767s. "Their skills and experience, or lack thereof, just weren't relevant."

"The hijackers required only the shallow understanding of the aircraft," agrees Ken Hertz, an airline pilot rated on the 757/767. "In much the same way that a person needn't be an experienced physician in order to perform CPR or set a broken bone."

That sentiment is echoed by Joe d'Eon, airline pilot and host of the "Fly With Me" podcast series. "It's the difference between a doctor and a butcher," says d'Eon.
http://www.salon.com/tech/col/smith/2006/05/19/askthepilot186/

Experienced pilot Giulio Bernacchia agrees:

In my opinion the official version of the fact is absolutely plausible, does not require exceptional circumstances, bending of any law of physics or superhuman capabilities. Like other (real pilots) have said, the manoeuvres required of the hijackers were within their (very limited) capabilities, they were performed without any degree of finesse and resulted in damage to the targets only after desperate overmanoeuvring of the planes. The hijackers took advantage of anything that might make their job easier, and decided not to rely on their low piloting skills. It is misleading to make people believe that the hijackers HAD to possess superior pilot skills to do what they did.

That’s the conclusion of his piece “Oh no! Not another expert!”, which you can read on the Other Contributions page under “Bernacchia”.