Originally Posted by
ATC Watcher
Last remark from PunkinDog on TCAS :
Both IFALPA and us fought hard on the ICAO FANS in the 90s.to keep TCAS where it belongs , a last minute anti collision system . It is not a separation tool and due to its poor azimuth definition ( +/- 11 degrees) it cannot be used for visual Aquisition. In my days when we issued a conditional clearance involving another aircraft and passed traffic info and the pilot replied, " we've got it on TCAS" we always replied, " fine ,but I need you to identifying visually this one ,by looking out of the window.
Remember that the one you see on TCAS might not be the one I am talking about.
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Reminder noted, but I believe anyone who's flown in the US outside Class A -> STAR -> Class B/C -> SID -> Class A understands that there's a whole lotta aircraft out that aren't the merely ones ATC tells us about, or is even talking to, or even has a transponder or ADS-B that ATC or our TCAS can see. The concept is well-ingrained and why FAA regs require looking outside to try and visually acquire traffic anytime flight conditions permit.
I hope nothing I wrote implied that TCAS be used as a separation tool. That would be like running a canyon high speed, low-level, and blind using a weather radar in ground mapping mode. It won't end well. I don't know any pilot that isn't aware of TCAS's limitations and inaccuracies between display vs the visual reality outside; we use it every day and it's been around for 30 years.
Only RAs should result in maneuvering, and that's been the case since US carriers were equipped with them by 91/93. I'm not sure who you were lobbying hard against in the 90's. UK/Europe was a late TCAS adopter in 2000 after which, for awhile anyway, there was still debate and training differences as to whether RAs took precedence over conflicting ATC instructions as the 2002 midair exposed. Hopefully, everyone is on the same page now.
TCAS display as a substitute for visual acquisition...absolutely not, of course. I know my long post is eye-glazing, but that is exactly the point for much of it. TCAS was the first thing on the list I mentioned those things that aren't a substitutes to acquiring traffic visually, whether the aircraft has been pointed out by ATC or not.
What I did say was that it's an aid that assists visual acquisition by directing attention to sectors of sky for scanning. That is literally the stated purpose of having Proximate, Unidentified, and Traffic Advisory symbols with relative altitudes shown on the display, with the TA alert designed to reduce the startle factor and response time if an RA occurs. Mere mortals can't tirelessly focus on everything everywhere all at once and we must prioritize duties and attention according to the situation. In the case of SFO when they're conducting parallel visuals the traffic call from ATC will usually come between the vector for intercept and clearance to fly the published Visual approach and the before intercept. If that traffic call is the first time someone looks outside to attempt visual acquisition of the aircraft they'll pair up with...because you know you'll be pairing up with someone...he/she might want to reconsider his/her priorities.
The problem isn't that the other aircraft ATC wants you to see can't be seen (at that point on the SFO visual it easily can be). The problem is that ATC has called out 1 aircraft but there may be 3 or 4 aircraft easily in view from the cockpit window, and if the traffic is low perhaps some ground lights could also confuse. The process of the brain differentiating between things one sees and compensating begins when first looking outside, so maybe the best time to begin that process isn't at 180 kts converging with the other aircraft when someone also needs to be minding the store confirming that the intercept is happening when it should. Life gets a lot easier if one begins to get the SA picture beforehand and allow the brain more time to process and differentiate in order to avoid what could otherwise be an initially-confusing picture later.
Visually mis-identifying aircraft has always been an issue long before the advent of TCAS, which in my opinion has reduced the likelihood. Pilots are fine with azimuth but estimates vary greatly when it comes to judging altitude differences relative to one's own, especially over slant range distances. At night you're looking for aircraft lighting against what may be a background of lights with all sorts of brightness, colours, and flashiness. Or it could be a hazy day with low sun in your eyes and the vis from where one sits is far more restricted than anything being reported. So if ATC calls out 1 aircraft but TCAS is showing 3 in that sector in close proximity and minimum vertical spacing (perhaps just 500" if 1 is VFR) your brain already accepts that the first 1 you spot visually may not be the one ATC wants you to identify so you continue to scan.
Low aspect targets are more difficult to see until close-in and if they're hot there's less time to visually acquire. Constant bearing crossing traffic has little or no relative motion. When ATC gives a traffic position it's not BRA but rather a Clock Bearing relative to flight path, not relative to aircraft heading, so unless there's zero x-wind component the traffic can possibly be positioned 1 or 2 clock sectors off. In daily use, I doubt there's anyone who doesn't reference the no-conflict Proximate Traffic targets and try to spot them, and in this way through familiarity makes one better at visually judging relative altitudes and slant range distances air-to-air because you have something inside the cockpit displaying their altitude.
Until ADS-B w/CPDLC is universally adopted, all aircraft equipped, and always-working worldwide, the TCAS info displayed to the crew will always be used for situational awareness monitor proximate traffic and, as such, sometimes for positioning where surveillance and/or ATC is sketchy or non-existent; there's still wake turbulence at altitude that may need offsetting from, the occasional oncoming traffic that's uncomfortably at or near your altitude that should be monitored, or CBs that need deviating around along everyone else having the same idea.
While TCAS certainly has its limitations it's not your grandpa's Pong game either, and It's better to have a slightly imperfect picture of those around you than no picture at all. In those places where ATC does exist but adhere to a funny, aviation-variation of the "Less is More" philosophy that prevents them from advising you of overtaking and/or nearby traffic because "You won't be able to miss seeing it soon anyway" or perhaps the gov doesn't have the funds to go around replacing worn-out ATC PTT switches, this also applies.
"We have him on TCAS", yes, yes, absolutely agree. An entirely useless response to a traffic call that does nothing but create uncertainly with the Controller (and everyone else) as to whether the pilot is looking outside for the traffic or not. I'm glad you brought it up, and perhaps we can all agree now's the time to establish a worldwide system of fining any pilot $500 (or pro crew $500 per head) for uttering it on the radio, paid into a fund that will be used for a yearly Pilot/Controller bash somewhere on neutral ground; a chartered 250' Feadship party boat floating on the Caribbean, for instance.
In fact, since the Authorities everywhere aren't doing anything about it and in the interests of getting the biggest boat possible, there should be an entire list of useless, annoying, and offending transmissions and their associated fines, the amount for each commensurate to its annoyance level. Something like;
1) We have him on TCAS ($500)
2) F*** ($1)
3) You have a stuck Mic ($1500 If repeated, + $5000)
4) Fully ready ($480)
5) ____ on the meter ($975)
6) Charlie Charlie ($ 328)
7) You're on Guard!!! ($ 2,500 + 3 Anger Management classes + 5-year Party Boat ban)
8) Animal noises (Entire estate + Death)
9) etc.
10) etc.