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The following reply to the protest letter available on
has been recently been received by a citizen.
This letter posted with permission on July 10 2000.
The letter is also available from the source at :

Dear Mr. ######,

Thank you for writing to me to express your concern about airborne condensation trails
(contrails) and reports of possible chemical spraying that create lines in the sky. I appreciate
knowing your concern on this issue.

I have contacted the relevant government agencies, including the Department of Defense
(DOD), the National Air and Space Administration (NASA), the Enviromental Protection
Agency (EPA), the Federal Aviation Administration (FAA) and the National Oceanographic
and Atmospheric Administration (NOAA) with your concerns. Each of the agencies verified
that contrails occur quite naturally in the wake of aircraft, as they have done since World War
II when aircraft began to fly at higher altitudes.

I also asked my Legislative Assistant for Military and Veterans Affairs to research this issue
further. He is a former naval avaitor with over 2000 hours of flight time and has significant
training in meteorology and physics.

The trails seen behind aircraft are formed by condensation. This is caused by the same
physical principles that cause us to see our breath or car exhaust on a cold day. As a aircraft
climbs, it will encounter temperatures approximately five degrees colder every one thousand
feet (this is called the lapse rate). Most aircraft operate at altitudes above 30,000
(approximately six miles), where temperatures are well below the freezing level even on the
most seasonal of days.

For engine exhaust contrails to form, it is necesary for the aircraft to fly through very cold
air, usually about minus forty degrees farenheit. The exhausted moisture and heat saturate the
air and condensation takes place almost immediately. The length of time for which a contrail will
be visible depends upon the relative humidity of the surrounding air. If low, the contrail may not
form or will disappear very quicky. In humid air, contrails can persist for many hours and have
been known to trigger the formation of a thin overcast of cirrus clouds.

As many have pointed out, another cause of why contrails might appear peculiar in
appearance is the patter in which they appear in the sky. Air traffic flows on “highways in the
sky,” referred to as airways. Just like roads on a map, airways intersect at airfields or
navigational checkpoints that are represented on navigational charts and defined by a lattitude
and longitude or by a range and bearing to an airport beacon. Therefore, contrails will often
appear in parallel or criss-crossed.

Finally, reoprts on the Internet and elsewhere claim links to a myriad of illnesses and
injuries; however, no data exists to back up these claims. The FAA, NOAA and the EPA, as
well as professors in universities around the country have examined these claims only to find out
that they were made by disreputable sources, who upon challenge have provided no evidence
or back up data.

I hope this information is of interest to you. Thank you again, for bringing your concerns to
my attention.


Richard G. Lugar
United States Senator