Pilot error, an air company's culture and its lack of a formal safety program were behind a fatal crash that killed nine people two years ago on sightseeing flight in Alaska, the National Transportation Safety Board determined Tuesday.

A pilot and eight passengers died June 25, 2015, when a de Havilland DHC-3 Otter operated by Promech Air Inc. crashed into mountainous terrain about 24 miles from Ketchikan, a city near the south end of Alaska's Panhandle.

The seaplane was returning from Misty Fjords National Monument, named for the low clouds that often cling to sheer cliffs rising from the fjords. The monument is a wilderness area of lakes, snowcapped peaks and glacier valleys. The eight passengers were on a side excursion from the Holland America Line cruise ship Westerdam.

Promech officials after the crash said pilot Bryan Krill, 64, of Hope, Idaho, had 4,300 hours of flight experience, including about 1,700 hours piloting single-engine seaplanes. However, the NTSB said the pilot had less than two months experience flying air tours in southeast Alaska and had difficulty "calibrating his own risk tolerance" for flight tours in marginal weather.

The day of the crash, the NTSB said, he continued to fly under visual flight rules when weather called for instrument flight rules.

Evidence collected in the investigation, the NTSB said, supported a finding that the pilot's decisions regarding his tour flights were influenced by schedule pressure, his attempt to emulate the behavior of other more experienced pilots, and Promech's organizational culture that tacitly endorsed flying in hazardous weather conditions.

"Lives depended on the pilot's decision making," NTSB Acting Chairman Robert Sumwalt said in a news release. "Pilot decisions are informed, for better or worse, by their company's culture. This company allowed competitive pressure to overwhelm the common-sense needs of passenger safety in its operations."

Promech's culture tacitly condoned flying under visual flight rules in hazardous weather and the company failed to manage risk associated with competitive pressures, the NTSB said.

Promech and at least one other operator that was willing to take more weather-related risks were able to fly more passengers than two more conservative operators who cancelled flights that day, the NTSB said.

Promech assets were purchased last year by another Ketchikan air service company, Taquan Air. Taquan was one of the two operators who cancelled flights the day of the crash. In an email response to questions, the company said visibility and ceiling requirements did not meet internal protocol for flying.

The passengers killed included Rowland Cheney, 71, and Mary Doucette, 59, of Lodi, California; Glenda Cambiaso, 31, of Montgomery County, Maryland, and her father, Hugo Cambiaso, 65; June Kranenburg, 73, and Leonard Kranenburg, 63, of Medford, Oregon; and Margie Apodaca, 63, and Raymond Apodaca, 70, of Sparks, Nevada.