On Saturday, January 9, 2016 at 11:54:33 PM UTC-8, Darryl Ramm wrote:
On Saturday, January 9, 2016 at 11:07:04 PM UTC-8, jfitch wrote:
On Saturday, January 9, 2016 at 5:47:04 PM UTC-8, XC wrote:
On Saturday, January 9, 2016 at 7:30:48 PM UTC-5, jfitch wrote:
On Saturday, January 9, 2016 at 12:08:39 PM UTC-8, XC wrote:
SNIPLet's make sure these numbers are based on some evidence.

Based on evidence presented so far, we don't even have a need for a stealth, so that is an odd statement.

The 5 second TCAS has got to be a minimum, panic mode number. Also do not just consider the case of one glider meeting one glider. Consider 5 gliders meeting 5 gliders. No longer can you just turn right or pull up, doing so may well cause an accident rather than prevent one.

More details about TCAS for comparison:

5 sec. is the maximum expected reaction time for a warning or RA. That is with the autopilot engaged and the pilot not actively engaged on the flight controls. The anticipated reaction time to reverse, increase or decrease vertical speed once the pilot is flying the machine is 2.5 sec.

"Initial vertical speed reaction to a RA is expected within 5 seconds; maneuvering G forces should be similar to those felt when responding to an ATC clearance to climb or defend "immediately" (+/- 0.25 G change in load factor)." That doesn't sound too panicked.

The TCAS display is selectable Above/Norm/Below. My company recommends normal in all phases of flight which gives +/- 2700 ft on the display. This is for aircraft capable of climbing or descending 6000 ft/min. "Above" can be selected in the climb which would give a view of aircraft 7000 ft above and 2700 ft below.

Now this is a different system, I understand, but my point is that it is not cross referenced continuously as a source of SA. Rather, it is an alert system that provides traffic advisories (TA) as aircraft are getting to be a factor ("Traffic") and resolution advisories (RA) ("Traffic, Climb/Descend)"when action is required by the pilot. The audio alerts and warnings have priority and have been determined to be more effective than the instrument panel display for collision avoidance.

Similarly, displaying all traffic on FLARM at these greater distances and relative altitudes is not required for SA or collision avoidance. In fact, spending too much time looking down at the display may be contrary to safety. Again, this discussion goes beyond collision avoidance and gets into pilots wanting to track other gliders for tactical reasons.

XC

In searching for the best anti collision system, few people hold out TCAS as the ideal. I have heard much more criticism of it than praise, the latter usually confined to "it's better than nothing". This is why the regulators and industry worldwide are moving as fast as they possibly can towards ADS-B, a system much more like Flarm. Before we decide that the metrics of TCAS are ideal or even adequate, we should ask why that system is being discarded in favor of one that shows all aircraft within 15 miles, all the time: position, altitude, and tail number. Going by that metric, the FAA has already decided that 15 miles range is the right answer. Even at 1000 mph closing speed, 15 miles gives over 50 seconds warning. I propose 50 seconds is the best supported number.

Oh what a pile of utter nonsense. TCAS II *is* the gold standard in collision avoidance. ADS-B does not replace TCAS II in *any* way. Not a single FAA regulation currently or proposed allows for replacement of TCAS II mandatory carriage with any ADS-B product.

TCAS II is not being discarded/abandoned for anything, including ADS-B anything. There is no technology that uses ADS-B for active collision avoidance similar to TCAS available as any RTCA standard and so nothing that can be build and no research projects that could be turned into such a standards any time soon. So at best anything based on ADS-B would likely be decades away. I have now idea where you are getting this 15 miles from. The ADS-B ground services hockey-puck diameter? That really has no direct relevance to TCAS. It is a stopgap layered on a complex dual-link mess.

TCAS II version 7.1 (the current standard) makes use of ADS-B In data to reduce the activeTCAS II transponder interrogation rates and provide better long range tracking of targets (esp. without excessive RF congestion). These systems do not use ADS-B data to issue an RA, that is all determined by active TCAS II to transponder interrogation. One of the specific advantages of Change 7.1 ADS-B integration is improved long range (much longer than 15nm you mention) traffic display... which in USA Class A airspace they will be able to rely on every aircraft being quipped with after 2020.

So not a single thing you stated is correct.

I should have said, "ADS-B is being incorporated into TCAS to make up for its shortcomings". According to reports, TCAS IV was abandon in favor of ADS-B enhancements. A couple of the main enhancements in question being accurate position, vector and ID information, precisely the things stealth advocates want to suppress. Whether we are talking about TCAS or ADS-B or ADS-B enhanced TCAS, there is not even a suggestion that the FAA thinks 5 seconds is adequate for anything but a last ditch panic maneuver.

There is a parallel in shipping collision avoidance, which depended on automated radar tracking aids for many years. This has been replaced in less than a decade by a GPS based digital network operated on VHF. No one I know wants to go back as it is far superior to radar tracking. In all of these systems, situational awareness is considered the first line of defense against collision, and automated warnings intended as a stop gap to cover cases where situational awareness was lost.