summary: anti-misting additive for jet fuel to avoid crash explosions

From: (Jonathan Thornburg)
Date:         27 Apr 95 02:53:16 
Organization: The University of British Columbia
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A few weeks ago I posted a query to this newsgroup

| Fire is probably the #1 hazard in (jet) aircraft crashes.  Puddles
| of spilled fuel aren't very flammable, but the mechanical and wind
| shearing of a high-speed crash tends to atomize spilled fuel, and a
| fine mist of fuel is highly explosive due to its huge surface/volume
| ratio.
| Some years ago, I read in some aviation magazine (nice ambiguous
| reference there :-) ) about an FAA project to develop an anti-atomizing
| fuel additive to reduce this fire hazard.  As I recall, the additive
| was a long-chain polymer (sort of like spagetti) which greatly increased
| the fuel's effective viscosity when rapidly sheared.  The system
| incorporated a "degrader" (I don't recall how it worked) to remove
| the polymer within the engines just before the fuel was burned.
| The additive and the equipment involved were fairly cheap (I recall
| ~$50K per aircraft, and less than 1% increase in the fuel cost),
| light (I think ~50 kg per aircraft), and worked well in tests.  Alas,
| when the FAA staged a test crash of a remote-controlled B720, the
| crash turned out to be a lot more violent than they planned, and the
| aircraft exploded in a fireball despite the additive.  (I remember
| a photo of the test crash in the article I read.)

and asking for more information.

Thank you to everyone who responded.  This posting is a summary of
the replies.

The degrader was a gear-pump device which chopped the polymer up into
small pieces.

For the test crash, the FAA had placed metal "can-openers" on the
ground to shear the wings open.  Unfortunately, the plane was slightly
off course and banking when it hit, and one of the engines struck a
can-opener, resulting in a big fireball.  Several people had seen
footage of this on a PBS program called "Why Planes Burn".  (Apparently
the fireball was actually somewhat less intense than it looked; the
paint on one side of the aircraft was only soot-covered, not burned.)

As to why the project was dropped, there seem to have been several
- The airline industry opposed the scheme on the grounds of cost.
  (As I should have pointed out in my original posting, even a small
  fraction of 1% fuel cost increase is considered very significant
  by the industry.)
- There were concerns about the possibility of incompletely-chopped-up
  polymer molecules from "normal" operation interfering with the
  fuel system in some unspecified manner.
- There were concerns about the possibility of the degrader failing
  in flight.  (This would cause the engines to clog and flameout.)
- The test crash was a spectacular failure.  One person suggested
  that this demonstrated that the underlying concept was invalid, but
  to me that seems an over-generalization from a single failure.  In
  any case, the failure certainly made it easier for the FAA to drop
  the project.
My own assessment is that (as with most cost-vs-safety tradeoffs in
the aviation industry) the cost concerns were the key factor.

Noone mentioned of any further work on this scheme after the FAA dropped
its project.

Fortunately, even with mistable fuel, per-boarding death rates in
scheduled air transport are still down around (world average) 1e-6
(~1e3 fatalities/year out of ~1e9 boardings/year worldwide), which
is pretty tiny.  I'm (a lot) more nervous driving for 1/2 a day on
a highway than flying across a continent.

(((I only get to read news once a month or so, so if you post a
followup to this article, please E-mail me a copy.  Thanks.)))

- Jonathan Thornburg
  U of British Columbia / Physics Dept / <>
  "Washing one's hands of the conflict between the powerful and the powerless
   means to side with the powerful, not to be neutral." - Freire / OXFAM