Question: How close are scenic flights allowed to fly to the rim of the Grand Canyon?
About the article "Grand Canyon", section "Activities".

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A variety of activities at the South Rim cater to park visitors.
The South Rim Drive () is a driving tour split into two segments.
The western drive to Hermit's Point is with several overlooks along the way, including Mohave Point, Hopi Point, and the Powell Memorial.
From March to December, access to Hermit's Rest is restricted to the free shuttle provided by the Park Service.
The eastern portion to Desert View is , and is open to private vehicles year round.
Walking tours include the Rim Trail, which runs west from the Pipe Creek viewpoint for about of paved road, followed by unpaved to Hermit's Rest.
Hikes can begin almost anywhere along this trail, and a shuttle can return hikers to their point of origin.
Mather Point, the first view most people reach when entering from the South Entrance, is a popular place to begin.
Private canyon flyovers are provided by helicopters and small airplanes out of Las Vegas, Phoenix, and the Grand Canyon National Park Airport.
Due to a crash in the 1990s, scenic flights are no longer allowed to fly within of the rim within the Grand Canyon National Park.
Several companies offer flights that land in the Grand Canyon in Hualapai Indian territory. 
Aside from casual sightseeing from the South Rim (averaging 7,000 feet [2,100 m] above sea level), rafting, hiking, running and helicopter tours are especially popular.
The Grand Canyon Ultra Marathon is a race over 24 hours.
The floor of the valley is accessible by foot, muleback, or by boat or raft from upriver.
Hiking down to the river and back up to the rim in one day is discouraged by park officials because of the distance, steep and rocky trails, change in elevation, and danger of heat exhaustion from the much higher temperatures at the bottom.
Rescues are required annually of unsuccessful rim-to-river-to-rim travelers.
Nevertheless, hundreds of fit and experienced hikers complete the trip every year.
Camping on the North and South Rims is generally restricted to established campgrounds and reservations are highly recommended, especially at the busier South Rim.
There is at large camping available along many parts of the North Rim managed by Kaibab National Forest.
North Rim campsites are only open seasonally due to road closures from weather and winter snowpack.
All overnight camping below the rim requires a backcountry permit from the Backcountry Office (BCO).
Each year Grand Canyon National Park receives approximately 30,000 requests for backcountry permits.
The park issues 13,000 permits, and close to 40,000 people camp overnight.
The earliest a permit application is accepted is the first of the month, four months before the proposed start month.
Tourists wishing for a more vertical perspective can board helicopters and small airplanes in Las Vegas, Phoenix and Grand Canyon National Park Airport (seven miles from the South Rim) for canyon flyovers.
Scenic flights are no longer allowed to fly within 1500 feet of the rim within the national park because of a late 1990s crash.
The last aerial video footage from below the rim was filmed in 1984.
However, some helicopter flights land on the Havasupai and Hualapai Indian Reservations within Grand Canyon (outside of the park boundaries).
Recently, the Hualapai Tribe opened the glass-bottomed Grand Canyon Skywalk on their property, Grand Canyon West.
The Skywalk has seen mixed reviews since the site is only accessible by driving down a dirt road, costs a minimum of $85 in total for reservation fees, a tour package and admission to the Skywalk itself and the fact that cameras or other personal equipment are not permitted on the Skywalk at any time due to the hazard of damaging the glass if dropped.
The Skywalk is about by road from Grand Canyon Village at the South Rim.
Grand Canyon National Park Airport is a state-owned public-use airport located in Tusayan, a CDP in unincorporated Coconino County, Arizona, United States.
It is near Grand Canyon National Park, seven miles (11 km) from the South Rim of the Grand Canyon.
The airport is primarily used for scenic tours and charter flights, but there is scheduled commercial service.
As per Federal Aviation Administration records, the airport had 294,436 passenger boardings (enplanements) in calendar year 2008 and 354,624 enplanements in 2007.
According to the FAA's National Plan of Integrated Airport Systems for 2009–2013, it is categorized as "commercial service - primary". 
The Grand Canyon North Rim Headquarters is a historic district on the North Rim of the Grand Canyon in Grand Canyon National Park.
Established from 1926 through the 1930s, the district includes examples of National Park Service Rustic architecture as applied to employee residences, administrative facilities and service structures. 
The National Transportation Safety Board found that the crews of the two aircraft failed to 'see and avoid' each other, but could not determine why this occurred due to the lack of recorded flight data (there being no requirement for such recording for the scenic flights that were being operated).
The accident investigation also found that the limited number of scenic points of interest in the Grand Canyon concentrated flights over these points, increasing the risk of collision; and recommended that the Federal Aviation Administration (FAA) regulate the separation of flight routes of fixed-wing aircraft and helicopters.
Following the accident the FAA imposed changes to the operation of scenic flights over the Grand Canyon.