The 1987 Overflights Act directed the National Park
Service to impose flight restrictions over Grand Canyon. They were also to study impacts
generated by overflying air-craft, and to prepare a report for Congress to determine
whether or not the new rules had substantially restored natural quiet to the Park.
Although that report is long overdue, preliminary findings from the research were made
available at the SFAR Oversight Group Meeting in Las Vegas on September 16th. The study
includes acoustic profiles and visitor surveys in Grand Canyon, Haleakala and Hawaii
Volcanoes National Parks.
Although 15 river sites and 8 rim sites were studied, the only results
distributed at the meeting were 2 studies of approximately 3 hours in duration. One was at
Deer Creek Falls and the other near the Little Colorado confluence.
The confluence lies beneath a flight corridor with commercial routes for both
helicopter & fixed wing tours. 23 aircraft were audible during the 3-hour study
period, which was divided into intervals of approximately 20 minutes. Aircraft were
audible during every interval, varying from 13% during the quieter periods to one in which
aircraft could be heard 94% of the time.
The site across from Deer Creek Falls, which lies within Shinumo
"flight-free zone", (no aircraft below 14,500 feet MSL), was much quieter,
although far from noise-free. On 9/3/92 during a 3-1/2 hour period, 13 aircraft were
audible. During one 20-minute interval, aircraft could be heard 36% of the time; only
during 3 intervals was there no aircraft heard.
Plotting noise levels is the easy part; determining how much they annoy
visitors is much more subjective. Let's say you ask a river passenger:
"Is that airplane disturbing you?"
"Well, I hadn't noticed it... but now that you mention it, yeah."
How much of the emotional response is generated by the question, and how much
is actually a result of the stimulus we are attempting to measure? Several air tour
operators have expressed concern that negative responses to aircraft noise have been
inadvertently solicited in this way.
The research depicts widely differing sensitivities to aircraft, depending on
duration of visit, location, percentage of time aircraft is audible, background noise,
group size, and the number of screaming babies nearby. Annoyance levels rise with decibel
levels of overflying aircraft; the trick is to determine the decibel range needed to stop
annoying people. There was only limited data available from the acoustic and dose-response
studies; researches promised that a forthcoming "Executive Summary" report will
be much more extensive.
GROUND VISITOR SURVEY
Most Park visitors reported hearing or seeing aircraft, with exposure
varying with the type of visitor use. Many visitors reported that the sound of aircraft
impacted their visit, again varying among user groups.
More than 90% of all visitors rated natural quiet as one of the most
important reasons for visiting the park. Yet many visitors reported that aircraft noise
reduced their opportunity to experience it.
AIR TOUR PASSENGER SURVEY
According to the survey, the main reason visitors took sight-seeing
flights was to see the Park from a "truly unique perspective".
One very interesting statistic was that 88% of air tour passengers also visit
the park on the ground. A common assertion by the air tour industry, that their passengers
impact park resources less than on-ground visitors, becomes moot. In addition, the
complaint that air tour passengers aren't paying their entrance fee to the Park is also
Half of the visitors who toured by land and air indicated that the visits
were equally important to their overall enjoyment. One-fourth felt that either the air or
ground visit was most important.
Most visitors recognized the value of some types of aircraft activity over
the National Park System. Almost all agreed that Park Management flights were appropriate.
Opinions concerning sight-seeing flights varied with the type of visitor.
In general, both land and air visitors favor management of aircraft activity.
If restrictions were determined to be necessary, they favored use of quieter aircraft, and
restricting the number of flights, airspace, and time of day. Less favorable options were
flying higher altitudes, and limiting days of the week or seasons of the year.
The National Park Service is hoping to have a final report within a couple
of months. Then there will be more meetings to decide just what to do about it, and that
won't be easy. The air tour industry has become increasingly defensive, environmental
organizations increasingly aggressive, and the governing agencies are caught in the
middle, often with their hands tied by conflicting laws and regulations.
What we need now is open communication, good suggestions, and a cooperative
effort to find a balance somewhere in the middle. There have been positive signs. After
angering the environmental community with some fairly outrageous remarks less than a year
ago in favor of air tours, FAA's Robert Trout has shown a pronounced attitude shift. At a
recent program for continuing education for pilots he stressed the need for
"throttling back" over noise sensitive areas. He asked pilots why they protected
their ears with "
those fancy $500 headsets? Because you're LOUD, that's
In a meeting last summer with Dan O'Connell of Kenai Air, we spread a map of
Grand Canyon across the hood of his car and discussed what routes might be less invasive.
"I don't want to fly over here", he said, "I know I'm making
people mad. But they say I have to."
Grand Canyon is a big place, we agreed. Let's work it out.