RTCA Special Committee 231 (SC-231) was tasked with looking into possible mitigations for controlled flight into terrain (CFIT) risk in general aviation and U.S. Federal Aviation Regulations Part 135 operations. They recommended development of a situational awareness tool based on NASA’s ground collision avoidance system (GCAS) technology. SC-231 considered a number of different options but settled on the GCAS-based tool because it could be developed in a relatively short period, there would be no regulatory issues to work through and using the product would be voluntary.
CFIT accidents are almost always fatal and are widely considered one of the highest risk accident types. While CFIT accidents in commercial aviation have diminished since the introduction of Terrain Awareness Warning Systems (TAWS), CFIT remains a stubborn problem in general aviation (GA) and other operations, killing dozens of people a year. FAA lists CFIT accidents second on it most recent list of top 10 leading causes of fatal GA accidents.
SC-231 was asked to address two National Transportation Safety Board (NTSB) safety recommendations, each of which resulted from investigations into fatal accidents in Alaska in which the aircraft crashed into mountainous terrains. In both accidents, the pilots had manually inhibited the Class B TAWS to avoid unwanted aural alerts.
In the first accident, on June 25, 2015, a single-engine, turbine-powered, de Havilland DHC-3 Otter on an on-demand sightseeing flight under visual flight rules (VFR) collided with mountainous, tree-covered terrain about 24 miles east-northeast of Ketchikan, Alaska, killing the pilot and eight passengers. Marginal VFR conditions were reported in the area at the time of the accident.
In its final report on the accident, NTSB issued safety recommendation A-17-35,which essentially called on FAA to implement ways to provide effective TAWS protections while mitigating nuisance alerts for single-engine airplanes operated under FAR Part 135 that frequently operate at altitudes below their respective TAWS class design alerting threshold.
In the other accident, which occurred on Oct. 2, 2016, Ravn Connect flight 3153, a turbine-powered Cessna 208B Grand Caravan, collided with steep, mountainous terrain about 10 nautical miles northwest of Togiak (Alaska) Airport. The two commercial pilots and the passenger were killed. The scheduled commuter flight was operated under VFR under Part 135. NTSB’s investigation determined that instrument meteorological conditions (IMC) were likely in the vicinity of the accident site at the time of the accident.
In its final report on the accident, NTSB issued safety recommendation A-18-15 to FAA to “modify the terrain awareness and warning system requirements in Technical Standard Order C151 such that, once the alerts are manually inhibited, they do not remain inhibited indefinitely if the pilot does not uninhibit them.”
SC-231 also was asked to consider a handful of recommendations from a working group of the public-private GA Joint Steering Committee.
SC-231 co-chairs Rick Ridenour and Yasuo Ishihara said the committee brainstormed a number of different ideas and recommendations and then ranked them based on advantages, disadvantages, cost and implementation difficulty. During the course of its work, the committee met numerous times virtually and three times in person, including once in Alaska, where it had a chance to present its recommendations to operators and gather their feedback.
In the end, the committee opted to recommend a technology that can be implemented relatively easily in personal electronic devices and which would include a display that shows an escape path to pilot navigating/flying in a confined area.
In its online materials, NASA says its improved GCAS leverages fighter safety technology and adapts its to civil aviation use as an advanced warning system. The technology supports higher fidelity terrain mapping, vehicle performance modeling, multidirectional avoidance techniques and user-friendly warning systems. In addition, the algorithms used in the technology have been incorporated into an app for tablet or other handheld or mobile devices that can by used by the pilot in the cockpit.
In 2017, RTCA published DO-367 – Minimum Operational Performance Standards (MOPS) for Terrain Awareness and Warning Systems (TAWS) Airborne Equipment, which was developed by SC-231.