Investigation Summary
The collision occurred as both aircraft were returning to Ketchikan from sightseeing tours of the Misty Fjords National Monument. The DHC-2 was level at 3,350 feet on a track of 255 degrees, while the DHC-3 was descending through the same altitude on a track of approximately 224 to 237 degrees. The NTSB's visibility study found that the DHC-3 was obscured from the DHC-2 pilot's view by the DHC-2's right wing and a passenger in the front seat. Conversely, the DHC-2 was obscured from the DHC-3 pilot's view by the left front window post for 11 seconds prior to the collision. Crucially, the safety net provided by ADS-B technology failed due to multiple factors. The DHC-3 was equipped with a Garmin GSL 71 system that had its auditory traffic alert feature disabled during a previous equipment upgrade. Additionally, the DHC-3's pressure altitude broadcasting was turned off because the control knob was in the OFF position, a setting not addressed by the operator's preflight checklist. Because the DHC-3 was not broadcasting altitude, the ForeFlight application used by the DHC-2 pilot failed to generate a conflict alert, as the software was not designed to alert on targets without altitude data. The NTSB investigation ultimately found that two simultaneous latent vulnerabilities within the equipment on the DHC-3 prevented either plane from generating a warning, highlighting gaps in the safety net that keeps small aircraft safe, gaps that claimed the lives of six people.
Final Conclusions
The NTSB determined the probable cause was the inherent limitations of the see-and-avoid concept and the absence of visual and aural alerts from both airplanes' traffic display systems. Contributing factors included the FAA's provision of transceivers that lacked alerting capabilities to Capstone Program operators without mitigating the loss of safety features, and the lack of a requirement for aural traffic advisory systems for Part 135 passenger-carrying operators. The final report was adopted on April 20, 2021.
Video Analysis
NTSB Ketchikan, AK Animation — Official NTSB animation exploring the flight paths, cockpit visibility obstructions, and ADS-B data leading to the May 13, 2019 mid-air collision.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Mountain Air Service N952DB — de Havilland Canada DHC-2 Beaver · N952DB
Taquan Air N959PA — de Havilland Canada DHC-3T Vazar Turbine Otter · N959PA
Crew Experience
Captain
Randy Sullivan, owner/pilot of Mountain Air Service.
Captain
Lou Beck, Taquan Air pilot and retired airline captain with 25,000 total flight hours and 15,000 hours as pilot-in-command.
Systems & Failure Modes
ADS-B / CDTI
Automatic Dependent Surveillance–Broadcast and Cockpit Display of Traffic Information. The DHC-3's Garmin GSL 71 had its aural alerts disabled and was not broadcasting altitude data.
ForeFlight
An electronic flight bag application used by the DHC-2 pilot; it did not provide alerts for the DHC-3 because the DHC-3 was not transmitting pressure altitude.
Interesting Facts
- 01The DHC-3 had not broadcast pressure altitude since April 29, 2019, due to an incorrectly set control knob.
- 02The DHC-2 pilot was the owner and sole pilot of Mountain Air Service, which ceased operations after the accident.
- 03Visual meteorological conditions (VMC) prevailed with clear skies at the time of the collision.
- 04A passenger on the DHC-3 saw the other aircraft and shouted a warning seconds before impact.
- 05The DHC-3 pilot was a retired airline captain with 25,000 hours of flight experience.
- 06The DHC-3 pilot held a first-class medical certificate with a limitation requiring the use of corrective lenses.
Safety Actions & Advisories
Part 135 SMS Requirement
The NTSB recommended that the FAA require Part 135 operators to implement Safety Management Systems (SMS) to identify and mitigate risks like equipment misconfigurations.
ForeFlight Software Update
The NTSB recommended that ForeFlight update its software to provide traffic alerts by default even when a target aircraft is not broadcasting pressure altitude.