Pentagon Research

Following the Sept. 11 attacks on the Pentagon and World Trade Center, President George W. Bush called for the creation of a system that would enable air traffic controllers on the ground to assume remote control of the aircraft and direct it to a safe landing at a nearby airport.

The military has employed this capability since the 1950s. Modifying and implementing the technology for use on passenger carrying aircraft in the United States would involve significant capital outlay, research and testing. But from an engineering standpoint, landing an aircraft automatically is a relatively simple matter.

“Autoland” systems have been in wide commercial use in different parts of the world since the 1980s. Auto landings are routinely performed thousands of times a day throughout the world.

Landing categories are broken down by minimum cloud heights, also known as the “ceiling," and the amount of horizontal visibility. There are three different categories of landing systems:

In all three categories of approach, the Flight Management System is entirely capable of landing the aircraft and, in some CAT IIIc-equipped aircraft such as the Boeing 747-400, capable of applying the brakes after touchdown and stopping the aircraft as well.

As for equipping an airliner for such use, the primary drawbacks are the mechanical systems, the flaps and landing gear, whose actuators are usually mechanical levers and/or switches in the cockpit. Retrofitting aircraft to allow for remote activation of these flight critical devices is possible but would be very expensive.

It is technically possible to create a system to perform remotely commanded return flights of a hijacked airliner. Onboard digital command, control and display equipment can easily share data with, and accept commands from, ground control stations. Little input beyond the initial command to enter safe return flight and the ultimate destination are needed.

Costs of retrofitting the existing airline fleet? Estimates range from $10 billion to more than $300 billion spent over a period of 10 years.

The most pragmatic approach? Design and install such systems into aircraft under development, and on current production aircraft design and install electronic interfaces and overrides.

Controlling the aircraft from the ground is nothing new. The military has been flying obsolete high performance fighter aircraft as target drones since the 1950s. In fact the North American Air Defense Command (NORAD) had at its disposal a number of U.S. Air Force General Dynamics F-106 Delta Dart fighter aircraft configured to be remotely flown into combat as early as 1959 under the auspices of a program know as SAGE. These aircraft could be started, taxied, taken off, flown into combat, fight, and return to a landing entirely by remote control, withhuman intervention needed only to fuel and re-arm them.

To this day, drone aircraft are remotely flown from Air Force and Navy bases all over the country to provide targets for both airborne and ground based weapons platforms.

The data links, which could be used for remotely controlling digital airborne flight control systems in commercial aircraft, are already in wide use. Known as ACARS (Aircraft Communications Addressing and Reporting System), this system is widely used to report everything from position and fuel burn, weather and flight plan information to ground stations. ACARS also has the capability of sending data to the aircraft.

Using this bi-directional data link would allow both uploading digital control inputs to control the aircraft as well as the potential to download and remotely monitor the digital aircraft displays.

In the past 20 years, progress in the field of avionics (AVIation electrONICS) has given end users the ability to safely navigate and communicate to and from virtually any point on, or for that matter above, the earth.

The most significant development is the fielding and proliferation of a satellite based navigation infrastructure, or Global Positioning System (GPS) originally intended for use by the U.S. military. GPS utilizes a “constellation” of satellites — 24 of which are in active use with three launched as spares, to provide incredibly accurate position information to end users.

Paralleling the widening acceptance of both the burgeoning GPS industry as well as the exponential increases in computer processing capabilities were two major developments in airborne navigation and display.

Cathode ray tube (CRT) displays, collectively known as Electronic Flight Information Systems (EFIS), were first fielded for civilian use in 1985. EFIS displays are essentially airborne computer monitors with the ability to “composite” information from a number of sources into a single display, something that cannot be done with traditional electro-mechanical instruments.

In essence, EFIS allows the crew to distill available information down to what a pilot needs to know at a particular time.

The downside of these displays is their expense: An 8-by-10 inch CRT tube used in a Boeing 747 class aircraft costs approximately $234,076, according to the 2002 Rockwell Collins price list. A 747 has six of these displays installed.

As “glass cockpits," as EFIS instrument panels called, gained acceptance, engineers designed flight management system (FMS) hardware and software that utilized faster and faster onboard computers to manage more and more onboard tasks.

FMS hardware is essentially a highly evolved autopilot. But where the autopilot was, in earlier times, a self-contained system, in today’s modern cockpits the autopilot is a sub-system that interpolates and executes commands generated by the FMS automatically, or by the pilot manually.

In everyday airline use, a flight plan is loaded into an FMS via either keystrokes on an alphanumeric pad, or via disc. This flight plan, pre-approved by, and filed with, the FAA will contain course, altitude and speed data that the aircraft will maintain at all points of its flight.

The format of the flight plan can be thought of as “point in space” data. In other words, the pilot flies the aircraft off of a runway and initially aims at a point in space that is a certain distance from, and at a certain altitude above the end of the runway he departed from. Upon reaching that point in space, which in most cases is an “intersection,” a point at which two major aircraft routes known as “airways” meet, the FMS will execute a turn, a climb, or combination of the two to the next point in space, and so on as the flight plan progresses.

Originally designed and built in large numbers during World War II, the autopilot has come a long was since the first commercially available unit, the Sperry H-2, a comparatively crude pneumatic mechanical and vacuum tube device that would hold a course and keep the wings level, more or less.

These days, a digital autopilot, in conjunction with systems that control the throttles, can effectively fly the aircraft from point to point with little or no input (beyond systems monitoring) from the crew.

Because all the components of controlling the aircraft communicate with each other digitally through a central unit, the FMS, activating such a “safe return” system would be a matter of uploading commands to the FMS to fly the aircraft to the nearest airport. Controlling the aircraft’s speed, altitude and course, the FMS would guide it back to land.