February 02, 2025, 16:54:00 GMT
permalink Post: 11819920
I know I'm fighting a losing battle but here goes.....
What you are doing wrong is making guesses based on incomplete/inaccurate data that is in the public domain.
Assuming the NTSB figure of 375ft is correct, you still need more info for it to mean anything. Was that the AGL, AMSL or SPS height/altitude?
How accurate are the 'various plots' that indicate the collision occurred mid-river? They may be right; they may not be.
Was the CRJ on final or was it still positioning to final? If it wasn't on final then the trigonometric calculations of what height it should be at might not be correct.
What official evidence is there that the Blackhawk made a 45 degree turn, or could that be a data error in the publicly available information?
In summary what I am saying is that, despite all of the internet sleuths plotting tracking data, none of it is official and it is all subject to various errors. Whilst interesting to form an understanding of the circumstances, it can't be assumed to be accurate to within a few feet (vertically or laterally).
That 1-2 feet error would be a theoretical accuracy. The readout in the cockpit would be subject to significant errors during turns/pitch changes etc; without knowing the exact installation on a Blackhawk, it might also unlock based on the surface conditions. More importantly, the ATC instructions would probably be based on an altimeter setting and not Rad Alt.
How would that have worked in this scenario? Who do you think should have been directed by TCAS to do what? Does the Blackhawk even have TCAS?
What you are doing wrong is making guesses based on incomplete/inaccurate data that is in the public domain.
Assuming the NTSB figure of 375ft is correct, you still need more info for it to mean anything. Was that the AGL, AMSL or SPS height/altitude?
How accurate are the 'various plots' that indicate the collision occurred mid-river? They may be right; they may not be.
Was the CRJ on final or was it still positioning to final? If it wasn't on final then the trigonometric calculations of what height it should be at might not be correct.
What official evidence is there that the Blackhawk made a 45 degree turn, or could that be a data error in the publicly available information?
In summary what I am saying is that, despite all of the internet sleuths plotting tracking data, none of it is official and it is all subject to various errors. Whilst interesting to form an understanding of the circumstances, it can't be assumed to be accurate to within a few feet (vertically or laterally).
That 1-2 feet error would be a theoretical accuracy. The readout in the cockpit would be subject to significant errors during turns/pitch changes etc; without knowing the exact installation on a Blackhawk, it might also unlock based on the surface conditions. More importantly, the ATC instructions would probably be based on an altimeter setting and not Rad Alt.
How would that have worked in this scenario? Who do you think should have been directed by TCAS to do what? Does the Blackhawk even have TCAS?
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ATC
Blackhawk (H-60)
CRJ
NTSB
TCAS (All)
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February 02, 2025, 17:33:00 GMT
permalink Post: 11819950
It could have instructed the CRJ to climb (meaning initiate go-around immediately) and the heli to ‘not climb’ (meaning descend if practicable). Or it could have instructed heli to climb and CRJ to not climb (meaning continue descent or level and look out). I am saying that tech is there in principle and the 500ft RA floor was decided on 20-30y ago, probably to limit complexity and risk of dangerous RAs, but that this limitation could be revisited in future, especially with lots more data and modelling capability to assess.
TCAS RA have inhibits at low altitude, or do you have some other system in mind?
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February 02, 2025, 18:05:00 GMT
permalink Post: 11819971
I know it is inhibited. I am saying that the concept of TCAS can be enhanced such that RAs are possible below 500ft without instructing one of the conflicting parties to fly into terrain. It may be worth looking at for safety engineers.
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February 02, 2025, 18:20:00 GMT
permalink Post: 11819978
In relation to your earlier response to my previous comment, how can the system tell someone to 'remain level' when that aircraft doesn't have TCAS? I am not sure of the Blackhawk fit, but I would be pretty surprised if it has TCAS fitted.
One of the main reasons that TCAS alerts are inhibited at low altitude is to avoid distraction during the landing phase, in an area that has a high traffic density and a high probably of nuisance alerts. The system would constantly be giving RAs and people would be going around and deviating all over the place. Even if just TAs were left active then it would be going off all the time, and we would be having the same conversation about becoming blase to the warnings as we are about the repetitive conflict alerts that were being given to the LC.
Getting TCAS to give RAs on final is not the solution in my opinion.
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Blackhawk (H-60)
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February 02, 2025, 18:46:00 GMT
permalink Post: 11819999
Do you honestly think that you've just thought of that and the system designers haven't?
In relation to your earlier response to my previous comment, how can the system tell someone to 'remain level' when that aircraft doesn't have TCAS? I am not sure of the Blackhawk fit, but I would be pretty surprised if it has TCAS fitted.
One of the main reasons that TCAS alerts are inhibited at low altitude is to avoid distraction during the landing phase, in an area that has a high traffic density and a high probably of nuisance alerts. The system would constantly be giving RAs and people would be going around and deviating all over the place. Even if just TAs were left active then it would be going off all the time, and we would be having the same conversation about becoming blase to the warnings as we are about the repetitive conflict alerts that were being given to the LC.
Getting TCAS to give RAs on final is not the solution in my opinion.
In relation to your earlier response to my previous comment, how can the system tell someone to 'remain level' when that aircraft doesn't have TCAS? I am not sure of the Blackhawk fit, but I would be pretty surprised if it has TCAS fitted.
One of the main reasons that TCAS alerts are inhibited at low altitude is to avoid distraction during the landing phase, in an area that has a high traffic density and a high probably of nuisance alerts. The system would constantly be giving RAs and people would be going around and deviating all over the place. Even if just TAs were left active then it would be going off all the time, and we would be having the same conversation about becoming blase to the warnings as we are about the repetitive conflict alerts that were being given to the LC.
Getting TCAS to give RAs on final is not the solution in my opinion.
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February 02, 2025, 19:00:00 GMT
permalink Post: 11820010
Do you honestly think that you've just thought of that and the system designers haven't?
In relation to your earlier response to my previous comment, how can the system tell someone to 'remain level' when that aircraft doesn't have TCAS? I am not sure of the Blackhawk fit, but I would be pretty surprised if it has TCAS fitted.
One of the main reasons that TCAS alerts are inhibited at low altitude is to avoid distraction during the landing phase, in an area that has a high traffic density and a high probably of nuisance alerts. The system would constantly be giving RAs and people would be going around and deviating all over the place. Even if just TAs were left active then it would be going off all the time, and we would be having the same conversation about becoming blase to the warnings as we are about the repetitive conflict alerts that were being given to the LC.
Getting TCAS to give RAs on final is not the solution in my opinion.
In relation to your earlier response to my previous comment, how can the system tell someone to 'remain level' when that aircraft doesn't have TCAS? I am not sure of the Blackhawk fit, but I would be pretty surprised if it has TCAS fitted.
One of the main reasons that TCAS alerts are inhibited at low altitude is to avoid distraction during the landing phase, in an area that has a high traffic density and a high probably of nuisance alerts. The system would constantly be giving RAs and people would be going around and deviating all over the place. Even if just TAs were left active then it would be going off all the time, and we would be having the same conversation about becoming blase to the warnings as we are about the repetitive conflict alerts that were being given to the LC.
Getting TCAS to give RAs on final is not the solution in my opinion.
And inhibition floor could still be greater than zero - say 100-200ft?
Separately, is it correct to say that CRJ were on final, or were they perhaps still turning onto final?
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February 02, 2025, 19:02:00 GMT
permalink Post: 11820013
Do you honestly think that you've just thought of that and the system designers haven't?
In relation to your earlier response to my previous comment, how can the system tell someone to 'remain level' when that aircraft doesn't have TCAS? I am not sure of the Blackhawk fit, but I would be pretty surprised if it has TCAS fitted.
One of the main reasons that TCAS alerts are inhibited at low altitude is to avoid distraction during the landing phase, in an area that has a high traffic density and a high probably of nuisance alerts. The system would constantly be giving RAs and people would be going around and deviating all over the place. Even if just TAs were left active then it would be going off all the time, and we would be having the same conversation about becoming blase to the warnings as we are about the repetitive conflict alerts that were being given to the LC. a
Getting TCAS to give RAs on final is not the solution in my opinion.
In relation to your earlier response to my previous comment, how can the system tell someone to 'remain level' when that aircraft doesn't have TCAS? I am not sure of the Blackhawk fit, but I would be pretty surprised if it has TCAS fitted.
One of the main reasons that TCAS alerts are inhibited at low altitude is to avoid distraction during the landing phase, in an area that has a high traffic density and a high probably of nuisance alerts. The system would constantly be giving RAs and people would be going around and deviating all over the place. Even if just TAs were left active then it would be going off all the time, and we would be having the same conversation about becoming blase to the warnings as we are about the repetitive conflict alerts that were being given to the LC. a
Getting TCAS to give RAs on final is not the solution in my opinion.
Nuisance go-arounds caused by RAs don't seem like a high price to pay to avoid this kind of catastrophic event. And perhaps nuisance go-arounds might cause some re-considerations of poor airspace design, such as this appears to be.
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ADSB (All)
Blackhawk (H-60)
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February 02, 2025, 19:25:00 GMT
permalink Post: 11820027
The current version of TCAS II is at least a decade old and, so far as I can tell from a cursory reading of the literature available online, does not incorporate ADS-B to the extent now possible. Given the massive improvements in processing technology since the current version of TCAS was finalized, it seems entirely possible that the issues cited here could be resolved with the proper engineering, as could many others (such as the 2024 Haneda crash). Retrofitting fleets (and requiring military aircraft to participate) would be a huge political problem, but there don't appear to be any showstoppers technically.
Nuisance go-arounds caused by RAs don't seem like a high price to pay to avoid this kind of catastrophic event. And perhaps nuisance go-arounds might cause some re-considerations of poor airspace design, such as this appears to be.
Nuisance go-arounds caused by RAs don't seem like a high price to pay to avoid this kind of catastrophic event. And perhaps nuisance go-arounds might cause some re-considerations of poor airspace design, such as this appears to be.
Going from TCAS II Change 7.0 to 7.1/7.1a was a simple matter of handing over enough cash to buy a couple of Porsches, for the new computer to effect a simple software change. What is irritating is the change was not an enhancement of the system it had all the hallmarks of incorporating the standard for TCAS at the time. An iPad with Foreflight or Garmin pilot an ADSB-in input is frankly more value when operating in the weeds, While we are at it, it is remarkable that Garmin Pilot and Foreflight provide better obstacle alerting than the certified EGPWS system does.
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ADSB (All)
ADSB In
TCAS (All)
TCAS RA
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February 02, 2025, 19:26:00 GMT
permalink Post: 11820029
Do you honestly think that you've just thought of that and the system designers haven't?
In relation to your earlier response to my previous comment, how can the system tell someone to 'remain level' when that aircraft doesn't have TCAS? I am not sure of the Blackhawk fit, but I would be pretty surprised if it has TCAS fitted.
One of the main reasons that TCAS alerts are inhibited at low altitude is to avoid distraction during the landing phase, in an area that has a high traffic density and a high probably of nuisance alerts. The system would constantly be giving RAs and people would be going around and deviating all over the place. Even if just TAs were left active then it would be going off all the time, and we would be having the same conversation about becoming blase to the warnings as we are about the repetitive conflict alerts that were being given to the LC.
Getting TCAS to give RAs on final is not the solution in my opinion.
In relation to your earlier response to my previous comment, how can the system tell someone to 'remain level' when that aircraft doesn't have TCAS? I am not sure of the Blackhawk fit, but I would be pretty surprised if it has TCAS fitted.
One of the main reasons that TCAS alerts are inhibited at low altitude is to avoid distraction during the landing phase, in an area that has a high traffic density and a high probably of nuisance alerts. The system would constantly be giving RAs and people would be going around and deviating all over the place. Even if just TAs were left active then it would be going off all the time, and we would be having the same conversation about becoming blase to the warnings as we are about the repetitive conflict alerts that were being given to the LC.
Getting TCAS to give RAs on final is not the solution in my opinion.
Fairly confident (and reported earlier) that the Blackhawk only has Mode S, so no ADS-B. Mode S may report less than ADS-B which means that position updates can be (but not always) significantly slower than ADS-B out. I also believe that for RA to work both aircraft would need to have both ADS-B In and ADS-B Out so that 2 way data communication can take place.
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ADSB (All)
ADSB In
ADSB Out
Blackhawk (H-60)
TCAS (All)
TCAS RA
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February 02, 2025, 20:31:00 GMT
permalink Post: 11820089
Fairly confident (and reported earlier) that the Blackhawk only has Mode S, so no ADS-B. Mode S may report less than ADS-B which means that position updates can be (but not always) significantly slower than ADS-B out. I also believe that for RA to work both aircraft would need to have both ADS-B In and ADS-B Out so that 2 way data communication can take place.
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ADSB (All)
ADSB In
ADSB Out
Blackhawk (H-60)
TCAS (All)
TCAS RA
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February 02, 2025, 20:59:00 GMT
permalink Post: 11820102
fdr, unless the Army did a after market install. The L model never had TCAS.
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February 02, 2025, 21:47:00 GMT
permalink Post: 11820135
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February 03, 2025, 03:25:00 GMT
permalink Post: 11820251
Instead of no RA below 500ft (or whatever the floor is), how about telling one conflict to climb and the other one to \x91not climb\x92? \x91Not climb\x92 could then be understood (and trained) to mean \x91descend a little, terrain/aircraft/wx permitting or fly level\x92. Lots of ifs and buts, spurious warnings, limitations for when 3 or more conflicts, TCAS vs. GPWS considerations etc. but perhaps worth a thought.
Instructing a climb could be useless or dangerous. Instructing no climb, same thing.
Engineering safety systems is not simple. You adjust one case, it can worsen another case.
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February 03, 2025, 16:25:00 GMT
permalink Post: 11820679
A few points, perhaps helping the Swiss cheese line up:
1) There seems to be a big push, especially in the US, to get traffic to go visual and do visual approaches, in order to squeeze in more traffic. I know of several European carriers that prohibit visual approaches at night. Is this really a sensible trend?
2) The design of the helicopter routes along the Potomac seem far from optimum. Noise or security concerns? I have seen many airports that prefer to hold helicopter traffic and then have it mid-field.
3) Hour and recency concerns. I know many insurance companies consider those with 500-1000 hours command to be in the highest risk category, as they have enough experience to get themselves in trouble, but not enough to get themselves back out of it. Also there are reports of the pilot flying being on an extended break away from flying, so what about recency?
4) Cockpit CRM gradient? I am not sure how things are in the military, but is there a CRM issue if the pilot being checked has the rank of Captain, and the pilot doing the checking is only a warrant officer?
5) Lots of talk about TCAS, but trying to fix low-level RA inhibits will create more problems then it will solve. I am sure they could come up with predictive, turning, variable climb rate RA\x92s, but these would then invariably be based on ADS-B data, which would then be subject to spoofing an create a whole host of new problems. Better not break something that is working well within it\x92s limitations.
1) There seems to be a big push, especially in the US, to get traffic to go visual and do visual approaches, in order to squeeze in more traffic. I know of several European carriers that prohibit visual approaches at night. Is this really a sensible trend?
2) The design of the helicopter routes along the Potomac seem far from optimum. Noise or security concerns? I have seen many airports that prefer to hold helicopter traffic and then have it mid-field.
3) Hour and recency concerns. I know many insurance companies consider those with 500-1000 hours command to be in the highest risk category, as they have enough experience to get themselves in trouble, but not enough to get themselves back out of it. Also there are reports of the pilot flying being on an extended break away from flying, so what about recency?
4) Cockpit CRM gradient? I am not sure how things are in the military, but is there a CRM issue if the pilot being checked has the rank of Captain, and the pilot doing the checking is only a warrant officer?
5) Lots of talk about TCAS, but trying to fix low-level RA inhibits will create more problems then it will solve. I am sure they could come up with predictive, turning, variable climb rate RA\x92s, but these would then invariably be based on ADS-B data, which would then be subject to spoofing an create a whole host of new problems. Better not break something that is working well within it\x92s limitations.
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February 04, 2025, 06:07:00 GMT
permalink Post: 11821131
Most likely the assumption is that in any conflict below 500\x92, the airplanes involved are in very low energy states.
Instructing a climb could be useless or dangerous. Instructing no climb, same thing.
Engineering safety systems is not simple. You adjust one case, it can worsen another case.
Instructing a climb could be useless or dangerous. Instructing no climb, same thing.
Engineering safety systems is not simple. You adjust one case, it can worsen another case.
All i am really saying is that:
(1) TCAS II can still be improved
(2) Other systems (like ADS-B) can, as can their adoption
(3) Interoperability between them can be enhanced
(4) Procedures can be improved (like mindset and division of tasks with TCAS TA on approach, especially in IMC and at night)
TCAS and ADSB took decades to implement and cost billions to fund but probably saved tens of thousands of lives by now.
And if certain vendors (Honeywell) have a monopoly that is up to regulators and policymakers to tackle (open standards, patent duration etc.)
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February 04, 2025, 07:34:00 GMT
permalink Post: 11821157
No threat in execution of TCAS climb in such conditions.
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February 04, 2025, 07:49:00 GMT
permalink Post: 11821166
Arguably all a low-energy state does is imply that TCAS needs to give RAs from further out. That of course further reduces throughput, unless you come up with additional ways to reduce false positives.
The end result of all of this, perhaps the better part of a century down the track, is probably going to be closer to positive train control and atlantic tracks: these are the blocks of airspace and time that are reserved for your aircraft, plus a buffer in each direction including time. Conflicting movements cannot be authorised (though unlike rail, you can have clearances that forbid you stopping, and therefore give a plane 'advance clearance' through a section of space that the plane(s) in front haven't yet transited, as long as the times each aircraft is allowed to be in that space are non-overlapping). At any time, an aircraft would expect to have forward clearances for 2-3 routes - normal path, plus pre-clearances for some combination of missed approach, engine failure drift-down, emergency descent, ETOPS divert, perhaps a even pre-authorised radio failure track. As you clear each section or a future clearance becomes unnecessary, you release it behind you but collect new clearances for alternate routes.
That's a long way away given even CPDLC is in fairly limited use.
I'm sure there's a few cases of stalls during go-around, terrain avoidance, or TCAS activation. There's never such a thing as 'no threat'. I do agree that it's pretty minimal, though, and the Airbus procedure of 'pull the stick full back and pray' simplifies/de-risks it even further.
The end result of all of this, perhaps the better part of a century down the track, is probably going to be closer to positive train control and atlantic tracks: these are the blocks of airspace and time that are reserved for your aircraft, plus a buffer in each direction including time. Conflicting movements cannot be authorised (though unlike rail, you can have clearances that forbid you stopping, and therefore give a plane 'advance clearance' through a section of space that the plane(s) in front haven't yet transited, as long as the times each aircraft is allowed to be in that space are non-overlapping). At any time, an aircraft would expect to have forward clearances for 2-3 routes - normal path, plus pre-clearances for some combination of missed approach, engine failure drift-down, emergency descent, ETOPS divert, perhaps a even pre-authorised radio failure track. As you clear each section or a future clearance becomes unnecessary, you release it behind you but collect new clearances for alternate routes.
That's a long way away given even CPDLC is in fairly limited use.
I'm sure there's a few cases of stalls during go-around, terrain avoidance, or TCAS activation. There's never such a thing as 'no threat'. I do agree that it's pretty minimal, though, and the Airbus procedure of 'pull the stick full back and pray' simplifies/de-risks it even further.
Last edited by Someone Somewhere; 4th February 2025 at 08:09 .
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February 04, 2025, 09:13:00 GMT
permalink Post: 11821217
P
All i am really saying is that:
(1) TCAS II can still be improved
(2) Other systems (like ADS-B) can, as can their adoption
(3) Interoperability between them can be enhanced
(4) Procedures can be improved (like mindset and division of tasks with TCAS TA on approach, especially in IMC and at night)
)
All i am really saying is that:
(1) TCAS II can still be improved
(2) Other systems (like ADS-B) can, as can their adoption
(3) Interoperability between them can be enhanced
(4) Procedures can be improved (like mindset and division of tasks with TCAS TA on approach, especially in IMC and at night)
)
1) TCAS II can still be improved : No end of the story by now , no version 8 in the pipeline . We spent millions and years on getting 7.1 accepted .. and even not everyone mandates it .
2) ADS-B gets already saturated , add TCAS type system and it will be .But developing a new Anti-collision system based on ADS-B is in the pipeline however it will; mean ASD-S be out mandated for every flying aircraft , including military . Here is your problem . Some military aircraft cannot be retrofitted , no space ..
3) interoperability .? No , 2 completely different systems , TCAS is analog 1970 technology ,
4) TCAS RAs on approach? you mean below 1000 ft ? No , in our scenario here , with the Blackhawk climbing , the logical RA would be a descent RA for the CRJ ,, you want a Descent RA at 300 ft ?
The only solution I personally see is airspace segregation based on equipment . Class A, B and C restricted to aircraft carrying ADS-B out and TCAS equipped , and both Working and on the MEL as no go item s ( not the case today ) Waiting for AOPA and ATA remarks
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ADSB (All)
ADSB In
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Blackhawk (H-60)
CRJ
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February 04, 2025, 09:36:00 GMT
permalink Post: 11821226
4) TCAS RAs on approach? you mean below 1000 ft ? No , in our scenario here , with the Blackhawk climbing , the logical RA would be a descent RA for the CRJ ,, you want a Descent RA at 300 ft ?
I think there is no problem for RA below 1000ft, it would only be like \x94TRAFFIC AHEAD, PULL UP\x94 in Airbus World. Horizontal separation might be smaller and system takes into account whether the traffic is between you and touch down. This DCA case is problematic because you join the final below 500ft, that is not acceptable in any case with an airliner.
TCAS 8 is getting closer and sooner after this horrific accident.
I think there is no problem for RA below 1000ft, it would only be like \x94TRAFFIC AHEAD, PULL UP\x94 in Airbus World. Horizontal separation might be smaller and system takes into account whether the traffic is between you and touch down. This DCA case is problematic because you join the final below 500ft, that is not acceptable in any case with an airliner.
TCAS 8 is getting closer and sooner after this horrific accident.
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Blackhawk (H-60)
CRJ
DCA
Separation (ALL)
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February 04, 2025, 10:43:00 GMT
permalink Post: 11821285
This means the automated tools (which don\x92t know the aircraft are using visual means to deconflict) will go off based on a predicted or actual loss of the separation criteria that they\x92ve been programmed with. If the helicopter in this instance had passed 1/4m behind and below the CRJ, a CA may still have been generated although the conflict had been resolved visually. The controller actually picks up on the apparent proximity and queries the heli that they are still visual, to which they reply in the affirmative - there is no minimum separation for visual avoidance, just sometimes it\x92s too dang close. Which is an Airprox.
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CRJ
IFR
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