Tuesday, May 1, 2012

Evaluation of New Obstruction Lighting Techniques to Reduce Avian Fatalities

DOT/FAA/TC-TN12/9 Author: James W. Patterson, Jr.

Evaluation of New Obstruction Lighting Techniques to Reduce Avian Fatalities

Wildlife biologists have conducted extensive research to better understand how migratory birds are negatively affected by
obstruction lights, which are used at night to warn pilots that they are approaching an obstruction hazard. The research concluded
that migratory birds appear to be attracted to the steady-burning (i.e., nonflashing) obstruction lights on communication towers
and, as a result, thousands of birds are killed annually through collisions with these obstructions. Wildlife organizations, the
telecommunication industry, and the Federal Communication Commission collectively approached the Federal Aviation
Administration (FAA) and requested that the FAA consider redefining their standards for obstruction lighting to either omit or
flash the normally steady-burning red lights to reduce their impact on the mortality rates of migratory birds.

In the research reported here, the FAA Airport Technology Research and Development Team evaluated the proposal to omit or
flash the normally steady-burning red lights. In addition, researchers evaluated the potential benefit of using light-emitting diode
obstruction lights instead of conventional incandescent obstruction lights as a way to mitigate their impact on birds, due to their
unique color and flash pattern. A series of flight evaluations was conducted to compare the obstruction lighting on several
communication towers in the northern Michigan area. A tower that was equipped with a nonstandard lighting configuration in
which the steady-burning red lights were programmed to flash in unison with the red flashing lights was also included in the
flight evaluation.

The results showed that flashing the steady-burning lights was acceptable for small towers (151 to 350 feet in height) and that
they could be omitted on taller towers (over 351 feet) so long as the remaining brighter, flashing lights were operational. The
optimal flash rate for the brighter lights to flash simultaneously was determined to be between 27 and 33 flashes per minute
(fpm). Flashing at slower speeds (under 27 fpm) did not provide the necessary conspicuity for pilots to clearly acquire the
obstruction at night without the steady-burning lights, and flashing at faster speeds (over 33 fpm), the lights were not off long
enough to be less of an attractant to migratory birds.

Based on the results of this research, the FAA proposes to make specific changes to the obstruction lighting standards, including
a proposal to omit or flash steady-burning red lights from several obstruction lighting configurations.

Author: James W. Patterson, Jr.

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