# Anti-Collision System for Small Civil Aircraft
## 2 Anti-Collision Systems
### Sense and Avoid Systems and Their Use in Small Civil Aircraft  
Depending on the technical equipment and characteristics of the targets in proximity, SAA technologies can be divided into cooperative and non-cooperative. There is an option to prescribe the duty of specific equipment on board aircraft but the Sense and Avoid System characteristics usually do not guarantee the possibility of use in all aircraft types. In this case, it is inevitable to broaden the problem to SWAP + PRICE as the additional possibilities of electronics and miniaturizations are significantly broad, but the price of smaller and lighter systems may be much higher. Actively cooperative systems incorporate query devices, and they monitor the sector in front of the flying object. Furthermore, they communicate with the query devices of other aircraft. This kind of system is capable of identifying the direction and distance to the aircraft and it is possible to employ it for flights subject to VFR. The key disadvantage of these systems is their significantly high price. Typical examples are various versions of ACAS systems. Actively non-cooperative systems employ laser or radar sensors to explore the sector in front of the aircraft systematically. The subsequent analysis of a signal reflected from the target makes it possible to calculate the distance, direction, and speed of mutual approaching. Disadvantages of such systems include weight and price. A passive cooperative system takes advantage of the fact that each aircraft automatically transmits its position, speed vector, and speed. In this case, the implemented sensor does not measure anything, it merely calculates the time to the moment of collision based on its speed and position. These systems are substantially simpler, cheaper, and lighter. Their disadvantage is that in areas with high-density air traffic, interference with their operation may occur. Another disadvantage is that it is impossible to detect targets that do not cooperate.  
Passive non-cooperative systems provide elevation and azimuth of surrounding targets. However, the systems are unable to identify the distance or speed of approaching sufficiently. The operation of passive non-cooperative systems is influenced by meteorological phenomena. These systems may be based on camera-like sensors. From the viewpoint of anti-collision technologies safety, it is not possible to employ a single solution as yet. Each technology has its advantages and disadvantages which have to be optimally balanced for a specific type of aircraft. At present, there are several options concerning equipping smaller aircraft with additional systems capable of efficiently operating as anti-collision systems. For the time being, TCAS II system is the only fully accepted anti-collision system of civil aviation and that is why it appears to be the most appropriate candidate for the implementation in this aircraft category as well. On the other hand, its applicability in the category of small aircraft is significantly limited by the financial factor. Other SAA systems are still in an early stage of their development and as such, they are unable to reach the prescribed goals dependably.