The pilots of two Alaskan sightseeing planes that collided in midair couldn’t see each other because airplane structures or a passenger blocked their views, and they didn’t get electronic alerts about their proximity to each other, because safety systems weren’t working properly.
That’s what the staff of the National Transportation Safety board found in its investigation of the May 2019 crash, which killed six people.
The board is meeting Tuesday in Washington to determine a probable cause of the crash and make recommendations to prevent it from happening again.
Mountain Air Service pilot Randy Sullivan and his four passengers, and a passenger in a plane owned by Taquan Air were killed. Ten people suffered injuries when the aircraft converged at 3,350 feet (1,021 metres).
The Ketchikan-based floatplanes carrying passengers from the same cruise ship, the Royal Princess, were returning from tours of Misty Fjords National Monument.
Mountain Air’s single-engine de Havilland DHC-2 MK 1 Beaver and Taquan’s larger turboprop de Havilland DHC-3 Otter collided just after noon over the west side of George Inlet.
Aircraft rely on “see and avoid” by pilots to prevent midair crashes, the staff said. And the crash occurred on a clear day in the afternoon.
But vice chairman Bruce Landsberg said the “see and avoid” system doesn’t work well in high traffic areas where the sight-seeing planes were travelling.
Chairman Robert Sumwalt read a statement of probable cause, which has not yet been approved by the board. He said the pilots didn’t see each other in time to avoid a collision.
Contributing factors included “preoccupation with matters unrelated to duties such as attempting to provide passengers with a scenic view and physiological limits on the human vision, reducing the time opportunity to see and avoid other aircraft,” he said.
Staff members told the board the Otter pilot recalled seeing a white and red flash, then a tremendous collision.
The Beaver pilot’s view would have been obstructed by the airplane’s structure and a passenger seated to his right during the critical moments before the crash. The Otter pilot’s view was obscured by a window post, the staff said.
Alerts not working in planes at time of collision
William Bramble, the NTSB’s human performance specialist, told the board that both planes were equipped with systems that track other planes, but visual and audible alerts weren’t working in either plane due to malfunctions.
“The Otter pilot seemed to miss seeing the target [the other plane] on the display because he last recalled looking at the
display about four minutes before the collision,” Bramble said.
Documents released earlier by the NTSB show the propeller of the Taquan Otter hit the other aircraft, leaving deep cuts later documented by investigators. The tail of the Mountain Air plane hit the left side of the Taquan aircraft, popping open a door.
The leg of a passenger sitting near the door was sucked outside the plane as other passengers held him in place, witnesses said.
Otter Pilot Lou Beck estimated his plane took five seconds to hit the water 10 miles (16 kilometres) northeast of Ketchikan.
At least three people could be heard saying, “brace brace brace,” on a camera recording audio before the Taquan plane hit the water.
The Mountain Air Beaver plane broke up in flight, scattering debris across 3,000 feet (914 metres).
Mountain Air Service closed after the accident.