Accident Overview
On May 13, 2019, at approximately 1221 Alaska daylight time, a float-equipped de Havilland DHC-2 (Beaver) airplane, registration N952DB, and a float-equipped de Havilland DHC-3 (Otter) airplane, registration N959PA, collided in midair about 8 miles northeast of Ketchikan, Alaska. The DHC-2 was operated by Mountain Air Service LLC under 14 CFR Part 135 as an on-demand sightseeing flight. The DHC-3 was operated by Venture Travel, LLC, doing business as Taquan Air, also under Part 135. Visual meteorological conditions prevailed at the time.
Flight Details
Both aircraft were conducting sightseeing flights to the Misty Fjords National Monument area and were converging on a scenic waterfall in the Mahoney Lakes area on Revillagigedo Island when the accident occurred. According to recorded avionics data from the DHC-3, it departed Rudyerd Bay about 1203 and followed the inlet westward. Automatic dependent surveillance-broadcast (ADS-B) tracking data began at 1213:08 for the DHC-3 and at 1213:55 for the DHC-2. At 1217:15, the DHC-3 was level at 4,000 ft msl over Carroll Inlet on a track of 225°, while the DHC-2 was 4.2 nm south, climbing through 2,800 ft on a track of 255°. The DHC-3 pilot reported checking his traffic display and seeing blue triangles not on his line, but did not observe the DHC-2 before the collision.
Collision and Aftermath
At 1219, the DHC-3 began descending from 4,000 ft while the DHC-2 climbed from 3,175 ft. Over the next 1 minute 21 seconds, the DHC-3 descended on a track between 224° and 237°, and the DHC-2 leveled at 3,350 ft on a track of about 255°. The DHC-3 made shallow turns before the collision at 1221:14 at an altitude of 3,350 ft, 7.4 nm northeast of Ketchikan Harbor Seaplane Base. The DHC-2 fractured into multiple pieces and impacted water and terrain northeast of Mahoney Lake. The DHC-3 experienced a brief upset in vertical load factor, entered a right bank, and descended, completing a 180° turn before impacting George Inlet at 1222:15. In the DHC-2, the pilot and four passengers sustained fatal injuries; the airplane was destroyed. In the DHC-3, the pilot sustained minor injuries, nine passengers serious injuries, and one passenger fatal injuries; the airplane sustained substantial damage.
Probable Cause
The National Transportation Safety Board (NTSB) determined that the probable cause of this accident was the inherent limitations of the see-and-avoid concept, which prevented the two pilots from seeing the other airplane before the collision, and the absence of visual and aural alerts from both airplanes' traffic display systems, while operating in a geographic area with a high concentration of air tour activity. Contributing to the accident were 1) the Federal Aviation Administration's provision of new transceivers that lacked alerting capability to Capstone Program operators without adequately mitigating the increased risk associated with the consequent loss of the previously available alerting capability and 2) the absence of a requirement for airborne traffic advisory systems with aural alerting among operators who carry passengers for hire.