Date: Fri, 20 Jul 2007 18:49:03 +0000
From: arc1@att.net (Richard Haines, NARCAP)
Subject: Lightning strikes and airplane crashes
To: nicap@insightbb.com, shg@mail.project1947.com


Dear Fran,
      You have asked some interesting and complex questions.  Here is some
information for your possible use:
 
     Documented crashes of airplanes due to lightning strikes:  (list not complete) 
       26 June 1959    Milan, Italy                   Lockheed Constellation
       8 Dec. 1963      Elkton, Maryland         B-707 (Pan Am)
       1981                 Germany                      commercial airliner 
       2000                 China                            commercial airliner
       22 Aug. 2006    Sukha Balka, Ukraine  Tu-154 commercial airliner  

     How Frequent is This event?  Statistical estimates vary as to the number of  times
       a given airplane is struck by lightning during a "typical" year.  Early estimates
       put the number at "slightly more than once per year" (ref. 1)  but more recent
       estimates by Boeing state "...every commercial airplane is hit by lightning on
       average about twice a year."  (ref. 2) 
           Because of the use of many techniques and materials the charge (estimated to
       be at least 200,000 amperes), is conducted effectively away from critical
       components and fuel tanks.  
           Considering the enormous number of commercial. military, and private airplane
       flights every day around the world, the probability of a crash caused directly by
       a lightning strike is extremely small.  I doubt very much that it has even been
       calculated. 

     Different Levels of Damage.  A Lockheed Field Service Digest (ref. 3) indicated
       that lightning can produce a variety of effects (although damage will be slight).
       Fortunately, there have been no recorded incidences of airplane passengers being
       killed  by lightning during a flight. External (aluminum skin) pitting and occasional
       (hole) puncture occurs.  The geometric vector of the lightning bolt relative to the
       aircraft's surface, relative aircraft velocity, conducting quality of the metal, and other
       factors determine the exact nature and appearance of these skin "burns" and arcing
       effects.  Another effect is transient.

              Radio and navigation equipment failure often occurs during a lightning strike.
       Modern commercial airplanes are so well shielded (grounded)  these days that
       such effects are typically transient and non-destructive.  Nevertheless, so-called 
       all glass cockpits employing computers and plasma instrument displays are more
       susceptible to transient, high current arcs. 

              Dielectric radomes are struck by lightning in flight.  The exact reason(s) is not
       yet known.  In addition to pitting and small holes literaly burned through the non-
       conductive material, the intense heat can expand and cause explosions into the
       shell.

              Protruding antennas are also commonly struck by lightning in flight. The charge
       can gain entry to the interior of the airplane along this pathway and expose personnel
       to hazardous voltage levels.  Much work has been done to develop spark-over
       arresters, dc blocking condensers, and static leak resistors to help control such effects.

              Hinged parts such as are used in control surfaces of airplanes are also susceptible
       to damage; bonding jumpers are attached between these surfaces and fixed portions
       of the fuselage.

      I'm sorry, but I'm out of time.  I hope this will help you in some way.
Richard F. Haines, Ph.D.
Chief Scientist
NARCAP


1.  www.lightningtech.com/d~ta/faq1.html
 
2.  Gates, D.,  Building the 787/When Lightning Strikes, Seattle Times, 5 March 2006.
3.  Turner, A.W., Lightning and Aircraft, Lockheed Field Service Digest, Issue 48, March 1964.