For once, almost unanimity!
I disagree with Avman: the topic has not been done to death. Indeed, from a scientific or engineering standpoint it has barely begun, even after a couple of decades. There are good reasons for this, some of which I mention below.
Nance's quoted remarks appear to be trivial and uninformed. If he really said that an airplane's electronic systems
Originally Posted by John Nance
all heavily shielded. That means that stray signals cannot get into those systems.
then he is *obviously wrong*.
Whether avionics can be affected by internal EM fields depends, most obviously, on the strength of the field: if I started up a tomography machine in the cockpit I can guarantee you that some things will go haywire.
The pertinent question for airline ops is whether avionics can be affected by field strengths of the order of those generated by portable electronic devices. What is known is
basically this: (1) that measured field strengths turn out sometimes to be greater than previously assumed, and (2) all the modelling codes have exhibited "spikes" at particular positions whose strength is orders of magnitude above the average field strength.
The newspaper may have been selectively quoting, but I hope Nance knows about the engineering work and will correct his statement.
I think there are two major pieces of work that anyone interested in this topic should know about.
One is the set of tests performed by the U.K. CAA some years ago, in which they measured the field strength of cell phone transmissions in various parts of an airplane, and found that in the cockpit area at least the field strength in some locations was stronger than previously supposed. The report is on the CAA WWW site.
The other is the extensive modelling work performed by NASA during the course of the TWA 800 investigation. A Harvard English professor, Elaine Scarry, proposed in a literary-political publication, the New York Review of Books, that EMI could have brought down TWA 800. The NTSB Chairman at the time entered into public correspondence about it. Result was a research contract to NASA to look at it. There are a few pages of the report devoted to the Scarry scenario, in which EMI came from outside the aircraft, and the bulk of it is devoted to the attempt to model fields generated *inside* the cabin. It is quite long, and you need to be an experienced numerical analyst to be able to glean useful information from it. It is in the TWA 800 docket, if this is still available on the WWW.
I worked with an electrical engineer, Willie Schepper, who assessed the possible effects upon experiments in the Department of Physics of extending tram service to the university here (the trams now run some 200m away from the building, rather than under it as first envisaged). He said that all the codes used for estimating field strengths in enclosed spaces are hand-me-down from the U.S. military, and obviously places like NASA get their hands on them first (partly because they are already used there when they are declassified). We advised the TSB on the SW111 investigation.
It is not trivial to perform assessments of the effects of fields in enclosed spaces, and claims to know with quasi-certainty (as the newspaper presents Nance) about certain effects should be treated with a dose of healthy scepticism.
Electric/electronic control systems, as ChristiaanJ says, are far more effectively shielded than nav gear or advisory systems such as TCAS which depend upon external signals. To my knowledge (although I can no longer claim to be up to date) there has not been one report of control systems apparently being adversely influenced by passenger electronics, whereas there have been thousands of such believable reports about nav gear coming from professionals who did their best to diagnose the problems in the air. The problem with verifying such reports is twofold: what happens in the air is different from what happens on the ground when the airline maintenance people try to test (different air pressure means different phenomena!); and the passenger whose untested electronic device may have been generating interference is usually unwilling to let his kit hang around the airport for a few days so that the airline can play with it. Neither of those two issues is ever going to go away. So one can continue to expect far more reports than can be definitively verified; it does not mean the phenomena were not present.
I heartily thank TwoOneFour for the TCAS interference report. I haven't been keeping up, but that is the first report about interference with a non-navcoms system I have read. (Or do we count TCAS as navcoms?)
PBL