Then point out all the time values not just the ones that seem to support your stance on stealth. TCAS Non threat traffic more than 6 miles away can be displayed to well over 40 miles away. Proximity intruder traffic less than 6 miles away fill in the diamond display(visual no audio) to get your attention and provide situation awareness to prevent surprise TA and RA alerts. Traffic Alerts (TA) for potential collisions will happen from 20-48 seconds to closest point of approach(collision) with a visual change to yellow diamond and audio "Traffic Traffic" Under normal conditions a TA will proceed an RA by 15 seconds which prepares the pilots for any required RA avoidance maneuver while giving time to acquire the target visually if possible. Resolution Advisories (RA) which TCAS deems an imminent collision threat with a time of closest approach of 15-35 seconds warns with a red diamond visual cue and audio avoidance commands (Climb Climb Climb, Monitor Vertical speed etc...) as well as the required vertical speed required for the 5 second maneuver you posted.


TCAS uses these multiple steps of awareness from well over 40 miles away to try and prevent surprise RAs as well as to give crews the time required to scan visually for the traffic. I also find it very hard to believe there have been many instant RAs without the targets going through the normal threat scales of non threat, proximity, TA, RA, Clear of Conflict or at least some of them. Does it happen yes but it is not the norm.

To suggest that your eyes are inside looking at the TCAS only because you are IFR is misleading. It gives you the fastest way of locating the direction and altitude of the potential collision traffic so you can then start looking visually for the traffic if your not in clouds. No one using TCAS gets a pop up TA and starts randomly visually scanning the sky hoping to see the traffic. It takes much longer than looking at the TCAS visual display for a split second to find out where the traffic is then back outside to find it visually.

This is exactly the same method that FLARM uses with a scaled response to traffic threats as they get closer and are deemed a threat. Both TCAS and FLARM allow much better situational awareness of traffic. I would argue that FLARM stealth mode is exactly like the pop up surprise TCAS RA example you used. It should never happen as there is only 5 seconds to respond. TCAS users get the advantage of a computer giving an immediately calculated escape maneuver. FLARM users only have seconds to find the traffic visually to find out what to do.

Sorry to not have done my homework better. The 5 seconds reaction time from holding a cup of coffee to change in vertical speed is the one give in our book at work. It is 2.5 sec with a little bit more G (+/- 0.35 G) to increase, decrease or reverse vertical speed. I didn't have any of those other numbers ready when I posted last night. The reaction times can be inferred as the "get moving" time. Add seconds as necessary to make the extra decisions needed for FLARM. How many more do you need? 10 sec?

TCAS II is a different system with a different criteria for what is "close".. To find this you have to get beyond the seconds and look at the protected distances which are also part of the equation. They apply when aircraft are closing slowly.

5000-10000 ft MSL TA= 0.75 nm or 850 ft vertical, RA = 0.55 nm or 600 ft vertical
10000-20000 ft MSL TA= 1.00 nm or 850 ft vertical, RA = 0.80 nm or 600 ft vertical

So you have to read between the lines a little, granted, but the above distances can be used to explain what TCAS thinks is a close call. The warnings are designed so the aircraft never gets any closer than this.

I think (I hope) we can agree that gliders routinely fly together inside of these distances without creating a bad situation. The times involved would logically be different.

A couple of other points to make about TCAS. Our display range is 6 or 12 nm. It routinely is set to show aircraft +/- 2700 ft. So all the tracking stuff is going on behind the scene and yes, TA's and RA's outside of those distances are show. But proximate traffic is not show beyond 12 nm on our installation.

XC