On July 10, 2018, about 0835 Alaska daylight time, a single-engine, turbine-powered, float equipped de Havilland DHC3T Otter airplane, N3952B, sustained substantial damage during an impact with rocky, mountainous, rising terrain about 9 miles west of Hydaburg, Alaska. The airplane was registered to Blue Aircraft, LLC and operated by Taquan Air as a visual flight rules (VFR) on-demand commercial flight under the provisions of 14 Code of Federal Regulations Part 135 when the accident occurred. Of the 11 occupants on board, the airline transport pilot was uninjured, four passengers sustained minor injuries, and six passengers sustained serious injuries. Marginal visual meteorological conditions prevailed, and company flight following procedures were in effect. The flight departed Steamboat Bay about 0747 destined for Ketchikan, Alaska. The area between Steamboat Bay and Ketchikan consists of remote inland fjords, coastal waterways, and steep mountainous terrain. During an initial telephone interview with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on July 11, the accident pilot reported that while in level cruise flight at about 1,100 ft mean sea level (MSL), and as the flight progressed into an area known as Sulzer Portage, visibility decreased rapidly from about 3-5 miles to nil. In an attempt to turnaround and return to VFR conditions, he initiated a climbing right turn. Prior to completing the 180° right turn, he saw what he believed to be a body of water and he became momentarily disoriented, so he leveled the wings. Shortly thereafter, he realized that he airplane was approaching an area of snow-covered mountainous terrain, so he applied full power and initiated a steep, emergency climb to avoid rising terrain ahead. As the steep emergency climb continued, the airspeed decayed, and the airplane subsequently collided with an area of rocky, rising terrain. During the initial impact, the airplane's floats were sheared off. The airplane wreckage came to rest in an area known as Jumbo Mountain, sustaining substantial damage to wings and fuselage. The pilot stated that the Terrain Awareness and Warning System (TAWS) was in the inhibit mode at the time of the accident. According to the passenger seated in the right front seat, after departure, they proceeded to Klawock and then made what he perceived to be as a 180° turn. He said there were numerous course deviations as they maneuvered around weather, and at times all forward visibility was lost as they briefly flew in and out of the clouds. He said he became uncomfortable and was thinking it would be prudent to just land on the water. Shortly thereafter, he observed a large mountain loom directly in front of the airplane, knowing they could not out climb the mountain he presumed there must be a pass through the area. As they continued to approach the mountain they entered a cloud and he observed the pilot add power and pitch up, but the airplane impacted the side of the mountain. According to a second passenger seated towards the back of the airplane, the weather at Steamboat Bay when they departed was rain and low clouds. During the flight he could occasionally see the land and water below, but sometimes he could not. He said that there was consistent serious fog all around. After they passed Waterfall Resort he became very concerned that they were headed in the wrong direction. He texted the right front seat passenger (a friend) and asked him to ask the pilot to land and wait for the weather to improve. He said that he did not see the mountain until they were right on it, and observed the pilot add power right before impact. At 0843, the United States Coast Guard (USCG) Sector Juneau received a report from the Alaska State Troopers (AST) that a float plane had crashed near Sulzer Portage on Prince of Wales Island. Two MH-60J Sea Hawk helicopters were launched from USCG Air Station Sitka, and AST activated the Ketchikan Volunteer Rescue Squad (KVRS) and other rescue personnel utilizing Temsco Helicopters, Inc. of Ketchikan. Five helicopters were dispatched from Temsco to the search area and a staging area was established near the believed to be accident site. One of the helicopter pilots stated that he was unable to search the upper levels of the mountainous area due to a low cloud ceiling and poor visibility. After receiving word that the USCG was approaching the search area, he returned to the staging area. A "First Alert" was received from the accident airplane's onboard emergency locator transmitter (ELT) at 0911. About the same time, 911 dispatch in Ketchikan talked to a survivor who provided GPS position and elevation based on data from her iPhone. At 1047 both USCG helicopters arrived in the search area and one helicopter obtained a weak direction finding (DF) bearing from the ELT at the crash scene. The DF bearing, and the survivor's description of the accident area were used to direct search assets in close proximity to the accident site, so the survivors could hear the USCG helicopters. Two-way radio communications were established between the survivors and USCG by utilizing the accident airplane's radio. The USCG located the accident site at 1156. At 1308 all 11 survivors had been hoisted into the USCG's rescue helicopter and transferred to the staging area for transport back to Ketchikan by Temsco Helicopters. The accident site was located on a rock face on the east side of Jumbo Mountain at an elevation of about 2,557 ft msl. All the airplane major components were located at the accident site. The closest weather reporting facility was Hydaburg Seaplane Base (PAHY), Hydaburg, Alaska, about 9 miles west of the accident site. At 0847, an METAR from PAHY was reporting, in part: wind from 110° at 13 knots; visibility, 5 statute miles in light rain and mist; clouds and sky condition, few clouds at 900 ft, overcast clouds at 1,700 ft; temperature, 57° F; dew point 55° F; altimeter, 30.16 inches of mercury. A detailed wreckage examination is pending.