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.


   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.


   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 largely incorrect.

   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 why."

   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.

Jeri Ledbetter