N3952B

HISTORY OF FLIGHT

On July 10, 2018, about 0835 Alaska daylight time, a float-equipped de Havilland DHC3T Otter airplane, N3952B, sustained substantial damage during impact with rocky, mountainous, rising terrain about 9 miles east of Hydaburg, Alaska. Of the 11 occupants on board, the airline transport pilot was uninjured, four passengers sustained minor injuries, and six passengers sustained serious injuries. The airplane was registered to Blue Aircraft, LLC, and was operated by Taquan Air as a Title 14 Code of Federal Regulations Part 135 on-demand commercial flight. Marginal visual meteorological conditions prevailed for the visual flight rules (VFR) flight, and company flight following procedures were in effect. The flight departed Steamboat Bay about 0747 destined for Ketchikan, Alaska.

The purpose of the flight was to transport guests that were staying at the Steamboat Bay Fishing Club on Noyes Island back to Ketchikan. The area between Noyes Island and Ketchikan consists of remote inland fjords, coastal waterways, and steep mountainous terrain. A review of GPS data extracted from the Chelton Integrated Display Unit (IDU) revealed that after departing Steamboat Bay the flight proceeded easterly towards the village of Klawock and to the northwest edge of Klawock Lake, prior to making about a 270° turn, it then continued on a southerly heading along the west coast of Prince of Wales Island towards Waterfall Seaplane Base (KWF) prior to turning easterly towards Hydaburg and an area known as Sulzer Portage.

Figure 1. Google Earth overlay of the entire accident flight on July 10, 2018. Indicated airspeed (IAS) values are shown.

For further information, see the Cockpit Displays – Recorded Flight Data Factual Report located in the public docket for this investigation.

According to the pilot, while in level cruise flight about 1,100 ft mean sea level (msl) as the flight progressed into an area known as Sulzer Portage, visibility decreased rapidly in heavy rain and clouds. In an attempt to turn around and return to VFR conditions, he initiated a climbing right turn. Before 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 the airplane was approaching an area of snow-covered mountainous terrain, so he applied full power and initiated a steep climb to avoid the rising terrain ahead. As the climb continued, the airspeed decayed, and the airplane subsequently collided with the mountain. During the initial impact, the airplane's floats partially separated from the fuselage. The airplane wreckage came to rest in an area known as Jumbo Mountain. When asked if he remembered any issues with the airplane, he replied "…the airplane was running great."

According to the passenger seated in the right front seat, after departure, the flight proceeded to Klawock and then made what he thought was a 180° turn. He said the flight made numerous course deviations as the pilot 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 directly in front of the airplane; knowing they could not outclimb the mountain, he presumed there must be a pass through the area. The airplane then entered a cloud and the pilot added power and pitched up, but the airplane impacted the side of the mountain.

According to a second passenger, who was seated toward 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 "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 that a float plane had crashed near Sulzer Portage on Prince of Wales Island. Two USCG helicopters were launched, and the Alaska State Troopers dispatched five helicopters to the search area; a staging area was established near the 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. A "First Alert" was received from the accident airplane's onboard emergency locator transmitter (ELT) at 0911. About the same time, a 911 dispatcher in Ketchikan talked via cell phone to a passenger, 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 bearing from the ELT. The bearing and the survivor's description of the accident area were used to direct search assets near the accident site, so the passengers could hear the USCG helicopters. Two-way radio communications were established between the passengers and USCG by using 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.

PERSONNEL INFORMATION

The pilot held an airline transport pilot certificate with airplane single-engine land and sea, multi-engine land and sea, and instrument ratings. A second-class airman medical certificate was issued on December 6, 2017, and contained limitations of must wear corrective lenses.

According to the operator's training records, the pilot was hired with 26,618 total hours of flight experience, including 2,700 hours of experience in Alaska. At the time of the accident, the pilot reported that he had accumulated about 306 hours in the accident airplane make and model. His most recent airman competency check, which was administered by a company check airman, was completed on May 13, 2018.

In June 2018, the pilot was on duty for 25 days and flew about 84 hours, with 5 days off. In July 2018, the pilot was on duty for 7 days, including the day of the accident, and flew about 28 hours, with 3 days off.

AIRCRAFT INFORMATION

The de Havilland DHC-3 Otter is a single-engine, propeller-driven, single-pilot, high-wing, short-takeoff-and-landing (STOL) airplane originally designed in the early 1950s. The original airplane was powered by a single reciprocating radial engine but could be converted to turbine engine power by supplemental type certificate (STC). The accident airplane was powered by a Pratt & Whitney Canada PT6A turboprop engine in accordance with Vazar, Inc., STC SA3777NM and equipped with International Aeroproducts Model 8100 floats in accordance with Anew Sioux Enterprises, Ltd., STC SQ01825NY. The type certificate for the airplane is currently owned and maintained by Viking Air Limited, Sidney, British Columbia, Canada.

The accident airplane was equipped with two Chelton Flight Systems FlightLogic electronic flight instrument system (EFIS) Integrated Display Units (IDU). The IDUs were identical part numbers and were configured to operate as primary flight displays (PFD) or multi-function displays (MFD). Using sensors, including solid-state air data and attitude heading reference system, the PFD displayed aircraft parameter data including altitude, airspeed, attitude, vertical speed, and heading. The MFD displayed navigational information through a moving map. Additionally, the units in the accident airplane included a terrain awareness and warning system (TAWS) that provided color-coded warnings of terrain on the MFD and, when enabled, aural alerts. As part of the TAWS system, the PFD was capable of providing a profile view of terrain ahead of the aircraft (synthetic vision).

The FlightLogic EFIS IDU features integrated Class B TAWS or, optionally, Class A or C TAWS or Class A or B Helicopter TAWS (HTAWS). The IDU provides TSO-C151b TAWS functionality. Depending upon aircraft configuration settings and external sensors/switches, the system is configurable as a Class A, B or C TAWS or a Class A or B HTAWS.4. The accident airplane's TAWS functionality was set to Class B specifications as required by 14 CFR 135.154 and Technical Standard Order (TSO) – C151. 14 CFR 135.154 (b) (2) states, "No person may operate a turbine-powered airplane configured with 6 to 9 passenger seats, excluding any pilot seat, after March 29, 2005, unless that airplane is equipped with an approved terrain awareness and warning system that meets as a minimum the requirements for Class B equipment in Technical Standard Order (TSO)-C151."

Although Class B TAWS specifies 700 ft agl during cruise flight and 500 ft during descent (as specified in TSO C-151c), the float-equipped accident airplane was authorized, per 14 CFR 135.203(a)(1), to cruise as low as 500 ft agl, which is below the Class B TAWS design alerting threshold. As a result, Class B TAWS auditory and flag alerts would be triggered during normal operations.

A TAWS inhibit switch, which was directly connected to the EFIS IDU, could manually inhibit the TAWS alerting function. The TAWS inhibit switch was a toggle type that provided the pilot with an obvious indication of actuation. The TAWS inhibit switch was found in the "inhibit" mode following the accident.

All of the company pilots interviewed stated that the TAWS inhibit switch remained in the inhibit position unless a controlled flight into terrain (CFIT) escape maneuver was being accomplished. However, the check airman who last administered the accident pilot's comp...