2
Performance Tradeoffs and the Development of Standards1
2.1 Scope of Sense and Avoid
The purpose of a sense and avoid (S&A) function is to act in the place of a human pilot to detect and resolve certain hazards to safe flight. These hazards consist of other traffic or objects presenting a risk of collision. Air traffic encompasses aircraft, gliders, balloons and even other unmanned aircraft system (UAS). Other hazards include terrain and obstacles (e.g., buildings, towers, power lines).
As there is no human pilot aboard a UAS, the motivation of S&A is not necessarily to preserve the aircraft but it is certainly needed to prevent collisions with other traffic, with persons on the ground, or collateral damage to property. S&A must operate for emergency and diversionary events as well as throughout normal operations.
On a manned aircraft, the human pilot is required to see and avoid hazards. The pilot's duties include regular visual scans across the forward field of view in order to detect other aircraft. The scanning may be more focused toward areas where operations are expected, or as informed by hearing radio traffic or by an electronic display. Whenever traffic is seen, the pilot must make a judgment about its trajectory relative to own aircraft motion, and determine whether any risk of collision might necessitate a maneuver. The ‘see and avoid’ process can be difficult in some conditions of poor visibility, confusing backgrounds ...
