Terrain Display Alternatives: Assessment of Information Density and Alerting Strategies
Executive Summary
Current technology makes navigation and terrain information available on electronic display screens in the cockpit. This
information must be presented clearly for pilots to maintain positional awareness and to avoid collision with terrain.
However, there are few recommendations or guidelines as to how electronic displays of information should be designed or
evaluated.
Electronic displays present enhanced information to the pilot which may help to reduce the accident rate in General Aviation
(GA) flight. For example, in the United States from 1983 to 1994, Controlled-Flight-Into-Terrain (CFIT) incidents accounted
for 32% of the GA accidents in instrument weather conditions. Enhanced real-time positional information on electronic
displays might help to prevent collisions with terrain.
The Volpe National Transportation Systems Center (Volpe Center), under the sponsorship of the Federal Aviation
Administration's (FAA's) Office of the Chief Scientific and Technical Advisor for Human Factors, AAR-100, conducted a
series of interrelated experiments to explore the human factors issues in depicting terrain on electronic displays. The
series of experiments examined instrument-rated GA pilots' ability to interpret terrain depicted on electronic plan view
displays using a flight simulator.
Because the resolution of electronic display screens causes a disproportionate relationship between the airplane symbol and
the terrain features, the initial experiment examined the utility of displaying nonthreatening terrain to pilots during
approaches. Participants flew the approaches accurately and did not veer off course despite the disproportionate size of
the airplane symbol relative to terrain features.
Terrain elevation information, presented on a supplemental plan view display, might prove useful to detect and avoid
dangerous terrain. In the second experiment, pilots failed to make use of the terrain information presented on an electronic
display. When they were presented with a display showing only terrain features, pilots showed heightened awareness to
terrain but not enough to take corrective action. When the display presented showed navigation and terrain information,
pilots failed to detect the dangerous terrain.
The third experiment measured pilots' preferences for information density on plan view electronic displays. Despite
findings that pilots may better recognize potential obstacles using displays with a lower density of information,
participants preferred the displays with higher content levels.
Visual alerts may enhance the interpretability of electronic plan view displays. In the final experiment, pilots used an
electronic display paired with a visual terrain alert. Using alternate map formats, the pilots were measured to see how well
they interpreted these displays to obtain terrain elevation information when there was a potential problem. The map formats
varied in terms of density of terrain and navigation information. The pilots were able to interpret the displays with equal
facility regardless of the map format.
This series of experiments addressed several human factors issues associated with presenting terrain information on
electronic displays. The summation of these points is that terrain information on electronic displays helps pilots to avoid
terrain if combined with a terrain alerting system, regardless of the information density of the map. These results suggest
that designs for display formats should incorporate alerts to make pilots aware of danger and reorient them quickly.
Display formats that incorporate these recommendations should contribute to a reduction in the number of accidents which
result from a loss of positional awareness, such as CFIT accidents. Further research into information presentation options
and systems and the benefit of training is needed.
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