Editor's Note: Roger Cox examine what led to the accident in Ketchikan, Alaska in this article. The accident investigation follows.
The NTSB conducted several tests and research projects to try to understand why both “see and avoid” and ADS-B failed to prevent the midair collision.
A performance engineer used recorded ADS-B data for both airplanes, three-dimensional laser scans of the cockpits of exemplars for both airplanes, passenger photos, and recorded avionics data on the DHC-3 to determine the position and orientation of the airplanes in the minutes before the collision.
The study showed the Beaver pilot’s view of the Otter would have been obscured by his aircraft’s cockpit structure, his right wing and his right-seat passenger. The Otter was above and behind him and he had no opportunity to spot it using a visual scan.
The Otter pilot’s view of the Beaver was also obscured by his aircraft’s window post. During the last 3 min. before the collision, there was a 24-sec. period when the Beaver would have appeared slightly ahead of the Otter’s left window post, but it would have appeared as a small, slow moving target below the horizon against a background of terrain and water. The rest of that time the Beaver was not visible to the Otter pilot. If he had moved forward 3 in., he would had been able to see the Beaver for 51 sec. The Otter pilot told investigators he did not look in the direction of the Beaver for the last 4 min. of the flight.
As pilots know, if a target on your windscreen is stationary, not moving left, right, up or down, you are on a collision course with it. However, small, stationary targets are hard to see, and you usually need some kind of alert to help you know where to look. There was no visual or aural warning for these two pilots.
Investigators first took both RANGR transceivers to the FreeFlight Systems facility for testing. The unit from the Beaver was connected to a test stand and powered on, and ADS-B In data was received and ADS-B Out data was transmitted. It worked. The Otter unit, however, proved to have had too much damage to function.
The FAA then provided recorded ADS-B data that had been transmitted to the nearest ground station by both airplanes before the collision. It showed the Otter had not transmitted pressure altitude or a valid transponder code since a flight on April 29, two weeks before the accident. After that flight, monthly maintenance had been performed on the airplane. No pressure altitude data had been transmitted on any subsequent flights. FreeFlight Systems personnel said the RANGR 978 receives pressure altitude from an encoder connected to the Garmin GSL 71, and if the unit is unpowered, no data is sent.
When the Otter wreckage was recovered, the control head selector knob for the GSL 71 was found to be off. Checking the GSL 71 control head was not part of the standard Otter preflight check and was not on a checklist. During the two weeks that the GSL 71 was turned off, the accident pilot had flown the airplane with both the Taquan chief pilot and several other Taquan pilots. No one had mentioned the need to turn on the GSL 71.
If the GSL 71 power switch had been on and selected to “ALT,” and the Beaver’s ForeFlight application was properly configured, the Beaver pilot would have received aural and visual alerts in time to avoid the conflict. The Otter pilot would have seen a filled cyan arrowhead on his Chelton navigational display, but the display would not have changed to a yellow filled arrowhead or generated a “traffic, traffic” aural alert as the airplanes approached one another.
The reason why the Otter’s system did not provide alerts lies in the long and irregular path of ADS-B development over the years and changes to FAA rules during that time. The ADS-B components originally installed in the DHC-3 in 2005 were installed as part of Phase 2 of the Capstone Program, funded by the FAA. The FAA’s decision in 2012 to upgrade the Capstone ADS-B equipment omitted the alerting function that had originally been there. It seems someone in the agency failed to appreciate the importance of traffic alerting in the real word of aviation.
To conclude their research, NTSB investigators did what I call a “what was and what could have been” study of the cockpit display of traffic information (CDTI) screens in the two airplanes. They show what the two pilots had on their displays and what they would have seen on them with full alerting function. The six graphical displays in the NTSB report are validation of the old adage that a picture is worth a thousand words. For pilots used to looking at screen displays, the graphics will bring to mind their own close calls. For pilots used to the traffic alert and collision avoidance system (TCAS) in larger airplanes, it will remind them of how often resolution advisories (RAs) have alerted them to a pending collision and how it helped to avoid those collisions.
Throughout the report and in the NTSB’s meeting, the effective use of graphics and animations help to make its work more accessible to the public than ever. For an excellent 10-min. video presentation of the Ketchikan accident, go to the NTSB’s web page on the accident and select “Animation on the NTSB YouTube Channel.” You can find it at https://www.ntsb.gov/news/events/Pages/2021-CEN19MA141AB-BMG.aspx
Findings and Conclusions
The NTSB found that the probable cause of the accident was “the inherent limitations of the see-and-avoid concept.” The Safety Board found no fault with the pilots. They said that to enhance collision avoidance, aural and visual alerting is necessary, especially in high-traffic areas. They added that all Part 135 aircraft should have ADS-B In and Out with these alerting systems and that the old Capstone avionics installations should all be checked to ensure they have alerting capability. They asked that the Airman’s Information Manual (AIM) and Pilot’s Handbook of Aeronautical Knowledge (PHAK) be updated based on this accident, and that alphabet aviation groups do likewise.
Finally, as has become routine with Part 135 accident reports, the NTSB recommended that these operators adopt safety management systems (SMSs).
One way of looking at this Ketchikan midair collision is to frame it as a classic failure of the defenses against an accident. There were gaps in organizational factors, there was unsafe supervision, there were unsafe preconditions and an unsafe act. The FAA failed to provide adequate separation services and regulation of technology and airspace. The air tour operators had an inadequate informal system to keep aircraft separated from each other. Taquan’s Otter checklist did not require the GSL 71 to be turned on and the Otter pilot wasn’t adequately trained. The Otter pilot arguably wasn’t vigilant enough in the crowded airspace. It would be easy to say that if the Otter pilot had just known to turn on the GSL 71, there would have been no accident.
While this “Swiss cheese” theory does explain the accident, it is unsatisfying to me. It doesn’t take context into account, and there is plenty of context to this accident. There have been 15 accidents in or near Ketchikan since 1996, and more in nearby areas like Hydaburg (Mount Jumbo) and Metlakatla. Taquan Air had accidents in 1998, 2007, 2012 and 2018, and an operator it acquired in 2015, Promech Air, had two more, one in 2002 and one in 2015. Counting the 2019 midair, Taquan and Promech have had 21 fatalities and numerous serious and minor injuries amongst its passengers since 1998. In addition, Taquan suffered another fatal accident one week after the midair collision accident.
Taquan Air is the largest floatplane operator in Ketchikan. According to the FAA operator registry, it currently has 10 airplanes on its Part 135 certificate. At one time it had a Part 121 certificate and 28 airplanes. The second largest operator over the last 20 years, Pacific Airways, experienced an accident in 2019 and closed its doors in 2020.
The natural risks in the Ketchikan area are numerous: mountains, fog, rain, ocean swells and tricky crosswinds, to name a few. The man-made risks are high too. Seasonal operation, turnover of pilots and chief pilots, recruitment of inexperienced pilots, and competition between operators for cruise ship passengers create risks. Slender FAA oversight resources lead to casual attitudes toward checklists and poor compliance with airspace user agreements. How else to explain omission of the GSL 71 switch on the Otter’s checklist? Why else was the accident Beaver level at 3,350 ft. when the airspace agreement said that flights returning from Misty Fjords should be at 500 ft., 1,500 ft., 2,500 ft. or hemispherical altitudes (4,500 ft.)?
It should be obvious that risks aren’t being properly managed in the Ketchikan air tour business. Maybe the introduction of SMSs will help. The post-COVID travel binge is just beginning. If the air tour business hasn’t made serious changes by the time the cruise ships return to Ketchikan, more accidents are likely.
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