So by way of resume, and to solicit peoples views, one aspect of this discussion which I find particularly interesting was developing as follows:
Very few light aircraft have "full" TCAS. Full TCAS, in addition to actively interrogating other aircraft, will provide the pilot with an RA, in other words what action to take if a collision becomes likely. (This is a simplistic explanation for the purpose of this discussion).
To keep down the price GA typically uses two different types of systems. The first (such as Skywatch) also actively interrogates traffic which is then displayed on a PFD (moving map) or stormscope showing the relative position of the traffic, its height, its change in height (relative to you) and the trend in its position relative to you.
PCAS on the other hand relies on piggybacking traffic information from ground based radar returns (in other words it is passive, and would not work in an environment without any other interrogators). In its simplest version it indicates range and altitude relative to you. In its more "advanced" version it also indicates direction, but only to the extent of the four quadrants relative to you.
PCAS has some other limitations. A return may not be received because it relies on a single antenna, whereas Skywatch has two antennas above and below the aircraft and mounted externally. PCAS is not approved and it is unclear how well the technology has been tested.
Skyforce typically offers the following level of accuracy:
Range accuracy 0.05nm (typical)
Bearing accuracy 5d rms (typical), 30d peak error
Altitude accuracy +/- 200 feet
I haven’t looked up the figures for PCAS.
FLAME is also used, particularly by the glider community, but very little within powered aircraft. It has some similarities with ADS-B.
I am familiar with the first two and have used both, but not with FLAME.
This discussion I think is relevant to all these systems.
Skywatch say that the intention of the system is to enable pilots to far more readily visually acquire conflicting traffic. They caution that separation should not be initiated until the traffic has been acquired visually. As far as I recall PCAS don’t say anything in their OM, but I may be mistaken (it is not to hand). I don’t know what FLAME say.
The discussion is should you do nothing until you visually acquire the traffic because of the inherent errors in range and bearing accuracy and because the other pilot might resolve the conflict in the same but opposite way to you. Only in the case of TCAS are expected to carry out an RA even if you have not visually acquired the traffic.
I think it is an interesting discussion as to how this might work in the GA environment giving the differences between TCAS and CAS.
What are the differences in environment.
Well for GA traffic outside CAS the traffic has complete freedom to manoeuver both laterally and vertically as it wishes. In other words as we all know there is no need to tell anyone that you are departing from your heading or altitude. Moreover other traffic often cannot be verified by reference to ground based radar because the traffic is not receiving any ground based service.
So the question is, in short, outside CAS do you make any adjustments to avoid an apparent conflict with other traffic based solely on CAS, or do you always wait until you have acquired the traffic visually however close that may mean you get.
I gave in the previous thread an example. You are enroute, VFR in 4k viz. Traffic at a range of 10k is converging your track at right angles, same height.
Do you:
React immediately either by altering course, height, or course and height,
or
Do you do nothing and wait until you have acquired the traffic visually how ever close that may take you?
Thoughts welcome from anyone using any of these sytems or just interested in how they work in a "non controlled" enviroment with the mix of traffic we are all accustomed to.