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Thwarting skyjackings from the ground

By Alan Staats
Posted to FACSNET Oct. 2, 2001
Published in Quill magazine {February 1998}

Automated airplane landing systems are advanced enough to bring a hijacked airplane 'home'

I. Introduction
II. How the system works
III. The bottom line
IV. History on remote control
V. Progress in technology
VI. A highly evolved autopilot
VII. Sources

Glossary of aviation terms

Technology now exists that could allow a ground crew to override and direct the flight path of a hijacked plane.

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 allow Air Traffic Controllers on the ground the ability 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.

žAutolandÓ 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.

How the system works

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

1. The "CAT IIIa" approach is flown by an aircraft equipped with three separate autopilot systems (one for actually commanding the aircraft, and two for backup) to a decision altitude of 50 feet, with at least 700 feet of horizontal visibility (referred to as RVR, or Runway Visual Range).› With this system, the crew must have visual confirmation that the runway is in sight, and that the aircraft is on course to land upon it, whereupon the autopilot system is disconnected and the pilot flies the aircraft to a safe touchdown.

2. CAT IIIb is a true autoland category, that is, the approach and landing touchdown are controlled entirely by what is known as a Flight Management System, or FMS. The crew must see the runway at an alert altitude of 50 feet with an RVR of 600 feet and verify that all three autopilots are on line and functioning correctly, and that the aircraft is configured to land, at which point the decision is made to allow the system to land the aircraft.

3. A CAT IIIc autoland approach has a higher alert height, 100 feet, then a IIIb landing, but a shorter RVR of 300 feet. Again, a final decision is made at the alert height to either continue the landing or abort.

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.

The bottom line

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 ten years.

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

History on remote control

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, NORAD (the North American Air Defense Command) 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, with the only human intervention needed being to fuel and re-arm them.

To this day, drone aircraft are remotely flown from Air Force and Naval 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, as well.

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.

Progress in Technology

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 žconstellationÓ 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 žcompositeÓ 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 eight by ten 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.

A 'highly evolved autopilot'

As žglass cockpits," as EFIS instrument panels are referred to, gained acceptance, engineers concurrently 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, for all intents and purposes.› However, where the autopilot was, in earlier times, a self-contained system, in todayŪs modern cockpits the autopilot is a sub-system that interpolates and executes commands generated by the FMS automatically or by the pilot, manually.

In every day 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 which the aircraft will maintain at all points of its flight.›

The format of the flight plan can be thought of as žpoint in spaceÓ 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 žintersection,Ó a point at which two major aircraft routes known as žairwaysÓ 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.

Autopilots, once a system into and of themselves in airline aircraft, have evolved as well.›

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 žsafe returnÓ system would be a matter of uploading commands to the FMS to fly the aircraft to the nearest airport.› Controlling the aircraftŪs speed, altitude and course, the FMS would guide it back to land.


  • Richard Vandam
    US Airways A320 Captain; Former Captain, U.S. Air Force, RF4-C pilot, Reno National Championship Air Races Air Boss and Chase Plane pilot, check and instructor pilot for vintage Cold War era Eastern Bloc fighter aircraft (MiG-15, -17, -21)
    Reno, Nevada. 775-742-5640 (cell), 775-851-1930 (home), e-mail

  • Aircraft Electronics Association
    Contact: Paula Derks, 4217 S. Hocker, Independence, MO 64055
    Phone: 816-373-6565
    Fax: 816-478-3100› email:

  • National Business Aircraft Association
    Main contacts:› Joseph Ponte, Jack Olcott
    1200 Eighteenth Street NW, Suite 400, Washington, DC 20036-2506
    Tel: (202) 783-9000› Fax: (202) 331-8364

  • FlightSafety International-Corporate Headquarters
    Contact:› James Waugh
    Marine Air Terminal, LaGuardia Airport, Flushing, NY 11371-1061
    (718) 565-4100,› (800) 877-5343 Fax: (718) 565-4174

  • Airline Pilots Association
    Contact: Gary Dinunno


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