Soft Walls: Frequently Asked Questions

Edward A. Lee

Technical Memorandum UCB/ERL M03/31, University of California, Berkeley, CA 94720, July 21, 2003.




In brief, modern aircraft all have electronics on board that is involved with the control and navigation of the aircraft. Many of the newer planes have computers on board that mediate the commands issued by the pilot and translate those commands into action, for example to bank and turn to the right. It is possible to modify the software in the computers in such a way that an airplane will refuse to enter pre-specified regions. We call these regions “no fly zones” and we call the boundaries of these regions “Soft Walls.” If an aircraft is equipped with the Soft Walls system, then if the pilot attempts to enter a no-fly zone, the airplane will be diverted. This happens gently at first, but if the pilot does not cooperate, then the system becomes more assertive. The key principle is to give the pilot as much control over the aircraft as is consistent with the constraint that the airplane does not enter the no-fly zone.

Since its introduction shortly after September 11, 2001, the Soft Walls concept has generated considerable controversy and discussion. This paper collects frequently raised objections to the concept and presents a discussion of the objections. A glossary is provided at the end.