The story...

There were no hijackers on the 9/11 planes. Instead they were flown by remote control.

Our take...

Remote control of large planes isn’t in itself a new idea. Successful tests have been carried out long ago, for example this experiment in 1984. However, some go further and say the Boeing 757 and 767 come with this ability already.

"The Boeing 757 and 767 are equipped with fully autonomous flight capability, they are the only two Boeing commuter aircraft capable of fully autonomous flight. They can be programmed to take off, fly to a destination and land, completely without a pilot at the controls.

They are intelligent planes, and have software limits pre set so that pilot error cannot cause passenger injury... No matter what the pilot wants, he cannot override this feature.

The plane that hit the Pentagon approached or reached its actual physical limits, military personnel have calculated that the Pentagon plane pulled between five and seven g's in its final turn.

The same is true for the second aircraft to impact the WTC.

There is only one way this can happen.

As well as fully autonomous flight capability, the 767 and 757 are the ONLY COMMUTER PLANES MADE BY BOEING THAT CAN BE FLOWN VIA REMOTE CONTROL. It is a feature that is standard to all of them, all 757's and 767's can do it.”
http://www.sianews.com/modules.php?name=News&file=print&sid=48

Unfortunately, it's mostly nonsense. The Boeing 757 and 767 do have autopilot, but turn it off and you can do what you like. What's more, the 757 and 767 do not have "fly by wire" capabilities (their control systems are mechanical, not electronic, with cables and hydraulics to move the control surfaces). The only plane that did at the time was the 777, and even this could be overridden by the pilot.

"On Boeing jets, the pilot can override onboard computers and their built-in soft limits.
"It's not a lack of trust in technology," said John Cashman, director of flight-crew operations for Boeing. "We certainly don't have the feeling that we do not want to rely on technology. But the pilot in control of the aircraft should have the ultimate authority.""
http://seattlepi.nwsource.com/business/boe202.shtml

But okay, let’s take this further. Maybe the planes were modified to be remote controlled. After all, America has remote controlled planes like the Predator and Global Hawk, so why couldn’t the technology be applied here?

Some people point to the planes final movements as indications of remote control. They talk about last minute corrections as planes flew into the WTC, or the difficulty of flying low-level into the Pentagon, as being far beyond the capabilities of the inexperienced hijackers. So is this really plausible?

We say no. Problem #1 is the major modifications that would be necessary to the plane, and the control system. You’d need some form of feedback to show the “remote controller” what was going on, perhaps several cameras, then a transmission system to send that fedback, and receive commands. All to be achieved without anyone noticing.

But that’s only the first issue. Consider this press conference reply from American General Ronald Keys:

Q: Referencing the E-10, if we can control a Predator from Nevada, why do we need to put a battle staff airborne in the E-10?

General Keys: Well, you can control them, but for example, we missed shooting down a MiG-25 during the war because of the latency in the system. We had the Hellfire-armed Predator up and the MiG-25 was coming in to intercept and we had him locked up, but by the time we had fired the missile, he had started his turn and so he broke lock. The reason was there's about a several second delay in the latency.
http://www.afa.org/Media/scripts/Keys_AWS05.asp

The “latency” the General refers to here is the delay any remote controlled plane faces. To take an example of flying into the Pentagon, what would happen if you appear to be coming in too low? First, there would be a delay while the cameras on board the plane processed the image. There’s then a delay while the image is transmitted, and another while it’s displayed to the remote pilot. There’s a natural delay while he reacts to the situation, then another in transmitting his commands back to the plane, and another while it adjusts the control surfaces accordingly.

How long is this delay, in total? The general says “several” seconds, and that was in February 2005, so may represent an improvement since 9/11. If we took “several” as being 3 seconds (and it could easily be more), then that would mean a plane flying 500 mph would cover around 2,100 feet, 0.4 of a mile, before it could possibly even begin reacting to anything the remote pilot has seen.

This lack of feedback makes remote control a risky business, as the Wall Street Journal reported (our emphasis):

Unmanned planes have proved invaluable in military operations, but their accident rate has added to domestic air-safety concerns. Predators, 27-foot-long propeller-driven planes which are among the biggest and best known drones in the Air Force, are used daily in Iraq and Afghanistan to track enemy targets with high-powered cameras and infrared sensors. Predators feed images to pilots on the ground or troops and are also equipped with missiles for their own attack missions. A recent report by the Congressional Research Service said their accident rate is 100 times that of manned aircraft, and noted that of 135 Predator unmanned surveillance-and-attack planes delivered and used in military operations, 50 have been lost and 34 more have had serious accidents.

To be sure, combat is different from commercial flight, but Air Force officials say that all of the crashes so far were the result of malfunctions or errors by pilots who are often as far away as Nevada and lack the sensation of being in the cockpit.
http://online.wsj.com/article/SB115491642950528436.html?mod=todays_us_marketplace

This doesn’t seem the most reliable technology, a major issue if you’re looking to pull off a complex plot involving multiple airliners. Of course we might theorise that the conspirators used some other kind system to remote control the aircraft, but that’s much more difficult than some people want to admit. Read Remote takeover on 9/11: A Critical Analysis by Jay H, an experienced avionics technician, to find out more.