Soundscapes: Overhead Flights

Aircraft overflights are one of the most common human-caused sources of noise in GCNP and can be heard almost everywhere within its boundaries.

Noise from aircraft can have a significant adverse impact on natural quiet, wildlife interactions, and visitor experiences. In 1975, the Grand Canyon National Park Enlargement Act recognized natural quiet as being an important part of visitors' experiences and sought to understand the impact of overflights on the park's soundscape. Subsequently, the 1987 Overflights Act required the "substantial restoration of natural quiet." The data collected by the Soundscape Program helps GCNP determine how well it is meeting the objectives of preserving natural sounds.

 

One of the criteria for substantial restoration of natural quiet (SRNQ) is that no more than 50% of the park may exceed 25% time audible.

These four rose diagram images below, from 2017, 2018, 2019 and 2020, demonstrate the percentage of park area exceeding this 25% time audible threshold, plotted on a polar axis. The length of the line indicates the maximum daily value of park area for that week, and the 52 weeks of the year are arranged clockwise on the plot. The daily maximum park area was chosen in place of a weekly average to prevent the situation where a peak value gets averaged down by the other days in the week. The limit of the plot is 50%, to show that no single day ever exceeds the SRNQ threshold.

 

2017 mid-March to mid-October show consistent values hovering around 30%. The off season values of park area are in the 10-15% range, with the notable spike around Christmas break. The Christmas spike peaks around 30%, which is similar to the summer month levels. Darker colored wedges represent a smaller area of the park being impacted; lighter colored wedges represent a greater area of the park being impacted.

 

2018 mid-March to mid-October show consistent values hovering around 30%. The off season values of park area are in the 10-15% range, with the notable spike around Christmas break. The Christmas spike peaks around 22%, which is below the summer month levels. Darker colored wedges represent a smaller area of the park being impacted; lighter colored wedges represent a greater area of the park being impacted.

 

2019 mid-March to mid-October show consistent values hovering around 28%. The off season values of park area are in the 10-15% range, with the notable spike around Christmas break. The Christmas spike peaks around 22%, which is generally below the summer month levels. Darker colored wedges represent a smaller area of the park being impacted; lighter colored wedges represent a greater area of the park being impacted.

 

2020 Overflights were dramatically reduced due to the COVID-19 pandemic and reduced visitation and air tours, which are reflected in the modeled noise levels in the park. Darker colored wedges represent a smaller area of the park being impacted; lighter colored wedges represent a greater area of the park being impacted.

 

The above graphics summarize the area of the park with audible overflight sounds greater than 25% of the time throughout the year for 2017, 2018, 2019, and 2020.

• “Substantial restoration of natural quiet” threshold (50% or more of the park achieving natural quiet, i.e., no aircraft audible, for 75% to 100% of the day, each and every day) was never exceeded on any day during these 4 years.

• During 2020, the park had the fewest overflights in the Dragon-Zuni flight corridors since we’ve been tracking this data (6,990 total operations), attributed to reduced visitation due to the COVID-19 pandemic. Quiet Technology aircraft (which is based on a per passenger noise average and not actual noise reductions) usage by percent of flights was 68.6% for 2020 (highest percentage recorded to date), compared to 55.5% in 2019 and 60.3% in 2018.

• Finally, the sound level (LEQ12, or the average sound pressure level during daylight hours) was the lowest during 2020 in our reporting history, 50.3 dB (compared to 57.3 dB in 2019 and 58.0 dB in 2018), which is consistent with the lower numbers of air tours.

Related Resources

• Grand Canyon National Park Overflight Documents

• Learn more about Air Tour management at the National Park Service Natural Sounds Subject Site.