The dramatic sweep of jagged mountains rising steeply from the pristine waters of America’s biggest national park is drawing a growing number of sightseers, but the increasing air traffic that comes with the aerial tours is concerning to veteran aviators and experts.

Two float planes had been returning to Ketchikan from a “flightseeing” tour to the popular Misty Fjords National Monument in Tongass National Forest Monday when they collided mid-air and crashed into the water below. Six people are dead, including an unidentified Canadian tourist and a pilot. Most were cruise ship travellers on an excursion.

"The fjords are very scenic, but at the same time, they can totally stop any radio transmission, so you may be only a mile or so from the other aircraft and not be able to get them directly until you get around the corner," points out veteran aviator and consultant John Goulet.

He points out that a few miles outside city limits, pilots rely on designated radio channels to communicate between each other in uncontrolled airspace, like much of Alaska. At a press briefing Tuesday afternoon, the U.S. Coast Guard said the survivors were rescued from the crash site 10 miles, or 16 kilometres, from the cruise ship base at Ketchikan, in a narrow fjord less than two kilometres wide.

Such mid-air collisions are extremely rare, prompting former Transportation Safety Board inspector and one-time Transport Canada regulator Bryce Fisher to suspect that the lack of instruments and reliance on visual flying came into play.

"It tells me both flight crews of both aircraft failed to see each other in order to avoid each other because they were flying in a fjord,” he said. “The whole idea here is about flying visually – (that) means in visual reference to the ground and water and looking out for other traffic in order to avoid them."

Both Goulet and Fisher referenced the increased air traffic in the area as increasing the likelihood of close calls or clashes between aircraft, but the operators themselves will also come under scrutiny.

The de Havilland Beaver was operated by Mountain Air, which has not responded to CTV News Vancouver’s request for comment. The Otter as operated by Taquan Air, whose surviving pilot will be questioned by investigators.

Taquan Air had operated a flight that crashed just last year, with the NTSB report on the incident noting visibility was an issue. Ten passengers and the pilot needed rescuing from the side of Jumbo Mountain in a dramatic operation 2,500 feet above sea level. In 2007, four passengers and a Taquan Air pilot died after one of their float planes slammed into the side of a mountain during a sight-seeing tour to the Misty Fjords. The NTSB report in that crash also noted visibility was an issue.

The rugged conditions, rapidly changing weather and surge in air traffic have Goulet advocating for better, newer instruments on float planes, something he acknowledges is difficult.

“The hardest part is putting the new technologies in [older planes] that enable them to fly safer in congested,” he said. “They can't really install the same quality of instrumentation and safety equipment that you can on a new aircraft, which is built to take the equipment."

The National Transportation Safety Board’s Jennifer Homendy told reporters investigators would be looking at everything from pilot logbooks and training to any potential medical issues the aviators might have, as well as maintenance records, company operating procedures and whether there were any other aircraft in the immediate area at the time of the crash. Neither cockpit nor data recorders were on board either aircraft, but they also weren’t required by law.

"Investigators will be on scene five to seven days,” said Homendy. “We will not be determining the probable cause of the accident in that timeframe, nor will we speculate on the cause."