Accident Overview
On June 18, 1986, at 0855 mountain standard time, Grand Canyon Airlines flight Canyon 6, a DHC-6 Twin Otter registered N76GC, departed from runway 21 at Grand Canyon Airport for a scheduled air tour over Grand Canyon National Park. The flight was planned to last approximately 50 minutes. At 0913, Helitech flight Tech 2, a Bell 2068 Jet Ranger registered NGTC, began its on-demand air tour from a heliport adjacent to State Route 64 near Tusayan, Arizona, about 5 miles south of the park's south rim entrance. Visual meteorological conditions prevailed.
The two aircraft collided at an altitude of 6,500 feet mean sea level over the Tonto Plateau. The DHC-6 carried 18 passengers and 2 crew members; the Bell 206 carried 4 passengers and 1 crew member. All 25 individuals on both aircraft were killed. Among the Twin Otter's 20 occupants were 11 citizens from the Netherlands and two from Switzerland.
Investigation
Due to the absence of cockpit voice recorders and flight data recorders in both aircraft, and a lack of radar data, investigators could not reconstruct the flight paths. Consequently, the reason why the pilots failed to see and avoid each other could not be determined.
The National Transportation Safety Board's report highlighted several systemic issues. Because of an exemption to 14 Code of Federal Regulations Part 135, local scenic air tours were conducted under Part 91. This investigation revealed that the Federal Aviation Administration provided no oversight on the routes and altitudes of Grand Canyon-based scenic air tour operators, contrary to the intent of Safety Recommendation A-84-52.
Additionally, the National Park Service, under a 1975 law, was studying the effects of aircraft noise on the Grand Canyon and simultaneously influencing the selection of air tour routes. Rotary-wing operators' routes were moved as a noise conservation measure to where they converged with those of Grand Canyon Airlines at the accident location.
Safety Issues
The investigation identified other safety concerns: the absence of regulations limiting flight and duty times for pilots conducting scenic air tours, and the lack of requirement for a cockpit intercom or public address system when pilots narrate during flights.
Probable Cause
The NTSB determined that the probable cause of the accident was the failure of the flightcrews of both aircraft to see and avoid each other for undetermined reasons. Contributing to the accident was the failure of the Federal Aviation Administration to exercise its oversight responsibility over flight operations in the Grand Canyon airspace and the actions of the National Park Service to influence the selection of routes by Grand Canyon scenic air tour operators. Also contributing was the modification and configuration of the routes of the rotary-wing operators resulting in their intersecting with the routes of Grand Canyon Airlines near Crystal Rapids.