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EMI and TWA800: Critique of a Proposal

Peter B. Ladkin

Article RVS-J-98-03
Elaine Scarry proposed that high intensity radio frequency fields (HIRF), possibly generated by the U.S. Military, be investigated as a possible causal factor in the TWA800 accident. Her argument appears to be very poor. I state it, and critique it.

This is a WWW version of an ASCII article in Risks-19.66 (Lad98-Risks-EMI/TWA) ,

Elaine Scarry has wondered whether electromagnetic interference (EMI -- she prefers the acronym HIRF, which she says stands either for High-Intensity Radio Frequency or High-Intensity Radiated Fields) could have been `the cause' of TWA800's crash in July 1996 (Sca98). She posits military activity in the area as potentially responsible for this HIRF. She identifies as possible sources a Black Hawk and an HC-130 within 5 miles horizontally and two miles vertically below TWA800; a P3 6,000+ft above; a C-141 and C-10 `in the vicinity', a Coast Guard cutter 15+ miles distant (and of course 13,700 ft = 2.5 miles below); an Aegis cruiser 180+ miles distant; and three submarines 70-200 miles south.

Piers Thompson contributed a pithy comment in RISKS-19.65 (Tho98) to the effect that 

[....]
I note from the paper itself that Elaine Scarry is professor of
"Aesthetics and General Theory of Value".  I don't know whether her
noted authorship includes any titles of relevance to air investigation
or EMI.

The paper itself makes a number of elementary errors of fact and relies
heavily on innuendo for effect.  It is far from a rational, scientific
review of the evidence.  The author claims that parts have been
subjected to scientific review.  It seems unlikely.

>
>    http://jya.com/twa800-emi.htm  (128K with 3 images)
>
>The article closely examines the possibility of electromagnetic interference
>in TWA 800's controls, comm, and black boxes by activities of the ten US
>military planes and ships in the vicinity which were heavily equipped for
>electronic warfare and were conducting tests of the gear.

The paper presents no evidence (and doesn't even claim) that the military
units were either "heavily equipped for electronic warfare" or "conducting
tests".
I find myself in sympathy with Thompson's comment and would like to contribute a few comments on Scarry's actual argument.

Omitting the surrounding packaging, she actually gives two concrete scenarios (1 and 3) and one supposition (2):

  1. Arcing from high-voltage to low-voltage wires, caused by a `pulse of energy' from outside the aircraft, caused the central fuel tank explosion;
  2. "Whatever evidence in the plane made lightning a possible candidate [for consideration as energy source for ignition] should make HIRF a candidate as well";
  3. "A sudden pulse of energy from a military jammer or countermeasures system could have acted to knock the plane out of control"

She wants the possibility of HIRF to become part of the TWA800 inquiry. Let's save the trouble and do it right here. One can show that investigating (1) won't lead anywhere; and (2) and (3) are completely implausible. Before the arguments, some background.

The breakup sequence of Flight 800 was initiated by the breakup of the Wing Center Section (NTSB97-TWA800-18A, Section 7.3) whose breakup sequence itself showed signs of an early `overpressure event' (NTSB97-TWA800-18A, Section 5.2.3). This means a central fuel tank explosion. Accordingly, one searches for the origin of the explosion, and this has not definitively been identified, so the investigation is still open. Hugh Chicoine has described to me (Chi98) that three factors must converge to form an `Ignition Sequence': available oxygen, a combustible, and a competent ignition source. I understand that the first two have been identified in the case of TWA800, and have led to the extensive research into flammable fuel vapors in central wing tanks of commercial aircraft. The search for a competent ignition source is open.

When inquiring about the possible effect of EMI on aircraft systems, it is important to distinguish, as Scarry does not appear to, between the various kinds of electrical systems on board aircraft: fly-by-wire (FBW) controls are different from navigation electronics, which are different from fuel pump electrics, which are different from the ovens used for heating passenger meals. She refers to a certain number of accidents to support her case: these occurred to Black Hawk helicopters (see e.g., (Coo87, Lad87, New87, Nor87, Woo87), and according to Scarry to F111s during the U.S. raid on Libya. I understand these accidents are believed to have emanated from EMI-FBW interference.

There is as yet no definitive incident with reproducible symptoms in which EMI is known to have interfered with commercial aviation navigation systems in navigable airspace, as far as I am aware, although there are plenty of plausible `anecdotes' ( Hel96, Lad97-Risks-EMI , Lad97-J-03 ). (There is the possible exception of cases in which aircraft violate airspace restrictions -- stay away from those microwave antennas :-). Also as far as I am aware there has been as yet no suspected incident of EMI interfering with electronic control (FBW) on commercial aircraft, but in the case of TWA800 this question is moot since the Boeing B747-100 is a `classic' aircraft with hydraulic and mechanical controls.

Electrics are generally more robust than electronics. The main potential ignition sources that have been considered are mechanical electrical sources; a pre-existing fire below the central wing tank; a bomb; a missile (NTSB97-TWA800-20A, Section 3, p5) . There was no evidence of a pre-existing fire, a bomb or a missile found. Potential sources explored include the electrical fuel gauging system; electrical power to the fuel pumps; a static electric charge/discharge; and `other systems' (NTSB97-TWA800-20A, Section 3, p6). "No evidence of electrical arcing or other mechanical failure signature has been noted on the hardware" (NTSB97-TWA800-20A, Section 3, final sentence, p9).

Finally, one should note that an aluminium aircraft hull acts as a significant barrier in each direction to electromagnetic radiation on radio frequencies. The original response to questions of EMI from passenger electronics pointed out that the nav receiver antennae were outside the hull, but the potentially damaging signals were supposed to come from inside the aircraft, and no one could see a way that those signals could have interference strength outside - they simply couldn't be powerful enough. Later inquiry has suspected imperfect or degraded interior avionics wiring connections (see Lad97-J-03, from RTCS-SC-177). As far as I know, no one has published estimates of what the field strength would have to be outside the aircraft in order to create that requisite field strength within the aircraft hull sufficient to cause arcing in any component of the fuel gauging system, fuel pumps or other such systems. Note that since no evidence of arcing was found, any arcing that did occur must have occurred in an item that was not recovered, despite an unprecedentedly thorough search -- and will not be recovered because the search has stopped.

This leads to the following commentary on Scarry's three suggestions.

  1. The inquiry has looked; no evidence of arcing was found; no evidence therefore will be found; the only thing that can be done is to calculate roughly the kind of field strength outside the aircraft that would be required to cause sufficient arcing inside the aircraft in the suspect but missing components. Any answer is going to be very rough and could not be correlated with any physical evidence; I suspect it could be calculated to a sufficient level of accuracy by some engineering graduate student with a little data from the component manufacturers who have already carried out such arcing tests. I would not expect the answer to lend any plausibility to the supposition that HIRF could have caused arcing. Whether or not, supposition it would remain since physical evidence there is not.
  2. A lightning strike contains enough energy to kill people it hits. It does not contain enough energy to kill people 100 yards away from a strike, unless one is happening to stand on a conduit without rubber soles. I've been this close to mountain lightning strikes twice without apparent arcing :-) A mile away from a lightning strike is even less of a problem. I don't know that even the military would consider discharging a Van de Graaf generator on a P3, even if they could fit one large enough in the fuselage. And I don't see how that remote and relatively mild event a mile away could be compared with a direct lightning strike on an aircraft. I find such a comparison .... um, implausible.
  3. The control on this aircraft is via cables and hydraulics. HIRF affects these not one jot. This is a truly stupid supposition.

So apart from finding the graduate student to do the calculation for the first supposition, what are the action items on Scarry's list? To get the `men and women in nearby planes and ships [to] describe the instruments in use that night'; and to have the USAF and DoD release classified studies they have done on how EMI affects military planes and ships. I'd judge she has a vastly underwhelming case - but then, she's the expert on the general theory of value, not I.

Peter Ladkin

References

(Chi98): Hugh Chicoine, Discussion on Private Mailing List, March 1998. (Back)

(Coo87): Brint Cooper, Jamming the Chopper, Risks-5.58, 15 November 1987, available at http://catless.ncl.ac.uk/Risks/5.58.html#subj3. (Back)

(Hel96): Albert Helfrick, Avionics and Portable Electronics: Trouble in the Air?, ( Acrobat PDF, 452K). Paper presented at the Aircraft Electronics Association Annual Convention, Nashville, TN, 1996. Avionics News Magazine, September 1996. Available from http://bluecoat.eurocontrol.fr, Public Reports, at http://bluecoat.eurocontrol.fr/reports/Helfrick_96_PED.pdf. Back

(Lad87): Peter Ladkin, UH-60 problems, Risks-5.59, 16 November 1987, available at http://catless.ncl.ac.uk/Risks/5.59.html#subj5. (Back)

(Lad97-Risks-EMI): Peter Ladkin, Aircraft and Passenger Electronics; FMS Nav Data, Risks-19.24, 16 July 1997, available at http://catless.ncl.ac.uk/Risks/19.24.html#subj7. (Back)

(Lad97-J-03): Peter Ladkin with colleagues, Electromagnetic Interference with Aircraft Systems: why worry?, Report RVS-J-97-03, 13 July 1997, available at http://www.rvs.uni-bielefeld.de. Also available in PDF format from http://bluecoat.eurocontrol.fr, Public Reports, at http://bluecoat.eurocontrol.fr/reports/Ladkin_97_EMI.pdf. (Back)

(Lad98-Risks-EMI/TWA): Peter B. Ladkin, Re: EMI and TWA 800, Risks-19.66, 9 April 1998, available at http://catless.ncl.ac.uk/Risks/19.66.html#subj6. (Back)

(New87): Dave Newkirk, Follow-up to Black Hawk Failures article, Risks-5.58, 15 November 1987, available at http://catless.ncl.ac.uk/Risks/5.58.html#subj2. (Back)

(Nor87): Lt. Scott A. Norton, Navy SH-60 Seahawk helicopters, Risks-5.59, 16 November 1987, available at http://catless.ncl.ac.uk/Risks/5.59.html#subj4. (Back)

(NTSB97-TWA800-18A): NTSB, TWA800 Docket: Exhibit 18A, Metallurgy/Structures Sequencing Group Chairman's Factual Report, Author, 1997, available through http://www.ntsb.gov/events/twa800/exhibit.htm. (Back)

(NTSB97-TWA800-20A): NTSB, TWA800 Docket: Exhibit 18A, Fire and Explosion Group Chairman's Factual Report, Author, 1997, available through http://www.ntsb.gov/events/twa800/exhibit.htm. (Back)

(Sca98): Elaine Scarry, The Fall of TWA 800: The Possibility of Electromagnetic Interference, New York Review of Books, Special Supplement, April 9, 1998, pp59-76. Also available at http://jya.com/twa800-emi.htm. (Back)

(Tho98): Piers Thompson, Re: EMI and TWA 800, Risks-19.65, 2 April 1998, available at http://catless.ncl.ac.uk/Risks/19.65.html#subj13. (Back)

(Woo87): John Woods, News article on EMI affecting Black hawk helicopter, Risks-5.56, 9 November 1987, available at http://catless.ncl.ac.uk/Risks/5.56.html#subj1. (Back)