Radar Page: 3 of 7

magyar_flyer
February 02, 2025, 15:44:00 GMT
permalink Post: 11819866

Quote:

Originally Posted by JohnDixson

Regarding UH-60L altimeters:
All UH-60 A and L Army aircraft incorporated the APN 209 radar altimeter. Our Sikorsky tech fellow for Avioics/electronis reports the accuracy in this area is 1-2 feet. The radar altimeter position in the instrument panel is just to the right of the attitude indicator and its top matches the top of the attitude indicator. The barometric altimeter is immediately below it.
Both pilots have the same setup.

Very useful tidbit.

So unless a very unlikely failures they knew their altitude within a few ft.

Subjects Barometric Altimeter Radar

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PPRuNeUser134364
February 02, 2025, 16:35:00 GMT
permalink Post: 11819905

I know I'm fighting a losing battle but here goes.....

Quote:

Originally Posted by DespairingTraveller

I'm struggling to make sense of the numbers being bandied about here. Apparently the NTSB has said that the CRJ was at 375 feet,

But from the beginning, various plots have shown the collision occurring in mid-river. A little work with Google Earth will show that the extended 33 centre line reaches mid-river about 3,300 feet from the aimpoint of runway 33. A 3 degree glideslope and some trig will put it at 175 feet at that range, with obvious implications. 375 feet would be a big error with not much more than half a mile left to run.

What am I doing wrong?

Also, helicopter route 4 hugs the eastern bank of the Potomac until Goose Island and doesn't cross to the western bank until Wilson Bridge. So why did the Black Hawk perform a 45 degree right turn while still abeam DCA? (See, e.g., post #25) Was it intending to route direct to Fort Belvoir, ignoring the heli routes? (I think I've seen it was operating out of Joint Base Anacostia en route to Fort Belvoir, so the fact it was still abeam DCA must have been more than obvious.)

Puzzled.

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).

Quote:

Originally Posted by JohnDixson

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.

Quote:

Originally Posted by uncle_maxwell

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.

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?

Subjects ATC Barometric Altimeter Blackhawk (H-60) CRJ DCA NTSB Radar Route 4 TCAS (All)

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JohnDixson
February 02, 2025, 17:57:00 GMT
permalink Post: 11819965

To follow Henra’s on point question: where was the call from the ATC radar monitoring, saying, for example: Army XXX you have traffic, 12 o’clock 1.5 miles coming at you, make immediate left turn to YYY, climb to WWW??
The reporting made public to date leaves the impression that ATC in this instance is the tower controller and only the tower controller.
Is it possible that radar guidance ( to either party ) has not surfaced because the single tower controller was not ( possibly could not? ) monitoring the tower radar display ( assuming that there was such ).
And, if there was such a display, was there software in place that incorporated a triggered warning when two aircraft tracks predicted an intersection?
NTSB will certainly be looking into these aspects.
( An aside re the barometric altitude accuracy fed to the radar system in the case of the non ADSB helicopter-assume this will be part of the after accident homework? )

Subjects ADSB (All) ATC NTSB Radar

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MPN11
February 02, 2025, 18:42:00 GMT
permalink Post: 11819995

@ JohnDixson \x85 thanks for that. Nobody that I can recall here has mentioned Tower having (or not) a slaved radar display from somewhere/someone. Lateral separation seemed to me a simple solution to the ensuing confliction, but \x85 is the TWR controller also radar rated? Could he legally even use the information that may have been presented to him (if such existed).

I had my Mil Tower and (DF) Approach ticket at least a year before I went on the GCA Course. OK, it was 1965 and no remote displays in Local, but would I have been legal to use what I could see?

Subjects ATC Radar Separation (ALL)

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Easy Street
February 02, 2025, 21:03:00 GMT
permalink Post: 11820111

Quote:

Originally Posted by The Brigadier

The CRJ700 was likely approaching Runway 33 at a heading of approximately 330 degrees, meaning it was moving northwest. The UH-60 Black Hawk may have been traveling at a heading roughly 240 to 270 degrees (west or southwest), which would place it on a near-perpendicular course relative to the plane.

If the aircraft were at a close to 90-degree intersection, then the CRJ700 would have been moving across the field of vision right in front of the helicopter, thus making the collision all the more perplexing, not withstanding night vision goggles (if indeed worn) interfere with depth perception and can reduce field of view to as low as 40\xb0. Of course there also remains the reported disparity in flying height, with the UH-60 100 feet above it's flight ceiling

See the marked up radar diagram at my #432 . I didn't annotate the CRJ's track, but the 33 centreline is 324 degrees true. The helo was turning from 187 to 189 degrees true, making it roughly a 135 degree track crossing angle: halfway between a head-on collision and a ninety. The final, constant bearing from the CRJ to the helo in the seconds before collision was 356. There was a slight left crosswind, so the CRJ would have had to look about 35 degrees right to see the helo. Meanwhile the CRJ was at least 11-13 degrees left of the helo's nose (more, given the westerly wind) and with the helo crew probably fixated on the A319 (AAL3130) to the south, they didn't see the CRJ until too late.

I can't access the METAR history any more, but I think it was 270V330 with gusts above 20kts. With the helo showing a groundspeed of 80kts on the radar trace, a westerly wind of just 12kts would give 9 degrees of drift and therefore a helo heading of 196, putting the CRJ just outside the 20 degree semi-angle of NVG with 40 degree field of view if the pilots were looking straight ahead.

If anyone can supply the METAR info (there was a report just 10mins after the accident), I'll update my radar diagram with the helo heading and a superimposed field of view. (Edit: done at #729 )

Last edited by Easy Street; 3rd February 2025 at 02:04 .

Subjects Blackhawk (H-60) CRJ Night Vision Goggles (NVG) Radar

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Easy Street
February 03, 2025, 01:52:00 GMT
permalink Post: 11820222

Thanks to DIBO and galaxy flyer for posting the weathers. I should have thought to go and look at ASN!

My marked up version of the radar plot now shows the heading of PAT25 at the first and penultimate sweep, based on the ground track as measured directly from the plot and assuming that the wind is at the non-gust value from the METAR observation taken just 4 minutes later (making this a reasonable minimum drift). It also shows the 40 degree field of view of the AN/AVS-9 NVG, drawn assuming both pilots are looking directly ahead along aircraft centreline.

The take-away is that with these assumptions, the CRJ starts on the extreme left hand edge of the NVG field of view and then moves just out of it. The PAT25 pilots would only see the CRJ in NVG if they turned their heads left of aircraft centreline to search for it. Since they thought they had visual contact, presumably with AAL3130, they would have no reason to do so.

Subjects CRJ Night Vision Goggles (NVG) PAT25 Radar

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YRP
February 03, 2025, 03:07:00 GMT
permalink Post: 11820246

Quote:

Originally Posted by henra

But why didn't the controller intervene then when the Helo kept closing in? What horizontal separation did he deem OK?

Radar is not that accurate. He wouldn\x92t be able to tell if the helo was going to pass, say, 1/4 mile behind.

And in fact he did speak up, asked the helo to confirm in sight. Obviously he saw it was close and wanted to check.

Unfortunately he didn\x92t quite say enough. If he\x92d said \x93traffic is 1/2 mile\x94 and the helo was looking at something 2 miles away, they might have twigged to it. Maybe.

Subjects ATC Radar Separation (ALL)

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Undertow
February 03, 2025, 13:35:00 GMT
permalink Post: 11820540

Quote:

Originally Posted by Torquetalk

The controller asks \x93what was the reason for the go around?\x94 That is standard.

The timing of the controller handover is surprising to me.

They'd already said "Tower, we had an RA. Brickyard 4514 is going around" and that was acknowledged. They were then switched to Potomac who confirmed radar contact and asked reason for go around again. I would hope Potomac had seen/heard the "CA". But then after this everyone just carries on as if this is all perfectly normal until we all know what happened the very next day.

Subjects ATC Radar Republic Airways Flight 4514 Go-around

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dukof
February 03, 2025, 14:07:00 GMT
permalink Post: 11820561

Quote:

Originally Posted by DaveReidUK

This was discussed earlier, with several posts being based on listening to an incomplete ATC recording which failed to pick up the (UHF) frequency on which the helicopter crew were responding.

As far as I can see, the helicopter crew when asked twice if they had the CRJ in sight responded in the affirmative both times. I think it's a tad unfair to criticise the controller for not being able to divine that they were actually looking at a different aircraft in the approach sequence.

"do you have the CRJ in sight" .."pass behind the CRJ" shows indeed he's uncertain of their awareness and wants them on a different heading. But the communication is completely inadequate to resolve the concern in the 15 sec time window left to intersection. It brings zero locational information of either the CRJ or the heading change they need to execute. The best possible outcome was clear to be a very near miss. With according to radar PAT at 200ft, CRJ descending from 500 at 600ft/min, and a 100ft radar resolution, there is zero margin here. So if you don't command a snap heading change at zero projected margin, at what point do you..?

Subjects ATC CRJ Close Calls Pass Behind Pass Behind (All) Radar

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YRP
February 03, 2025, 14:45:00 GMT
permalink Post: 11820598

Quote:

Originally Posted by dukof

Yes the controller was concerned enough to check again, not alarmed though.

But the controller doesn\x92t know they have the wrong plane. Guess: he\x92s just checking they didn\x92t think they\x92d passed it already.

Either way, the controller does not have enough information to use a heading \x97 neither to know one is needed nor what it should be . The radar & display is just not as accurate as a Mark I eyeball in one cockpit seeing the other plane out the window.

When would he? \x93Tower, PAT25 has lost that traffic\x94. Until then a vector might bring them *into* a collision.

Subjects ATC CRJ Close Calls PAT25 Pass Behind Pass Behind (All) Radar

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ATC Watcher
February 03, 2025, 15:42:00 GMT
permalink Post: 11820640

Quote:

the controller does not have enough information to use a heading

Quote:

flight recorder show the collision occurred at an altitude of about 325 feet, plus or minus 25 feet.

25 ft is the accuracy of mode S, transmit data so let's take 300 ft , Heli was apparently 100 ft higher than its altitude restriction , doing a separation maneuver ? (*) question to my US friends , : when delegating separation VFR to an aircraft does that automatically cancels its previous altitude restrictions ?
(*) I mean control input to maintain visual separation . not last second collision avoidance maneuver.

Subjects ATC FAA ICAO Radar Separation (ALL) VFR Visual Separation

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island_airphoto
February 03, 2025, 16:32:00 GMT
permalink Post: 11820688

Quote:

Originally Posted by ATC Watcher

Not 100% sure about the US FAA situation where everything seems to be possible , at least in DC, but in ICAO land Tower controllers cannot give headings, while they might have a copy of the Approach radar picture on a TV monitor somewhere , it is to verify actual positions not to issue vectors.. In addition some TWR controllers are just TWR rated, not Approach radar rated.

25 ft is the accuracy of mode S, transmit data so let's take 300 ft , Heli was apparently 100 ft higher than its altitude restriction , doing a separation maneuver ? (*) question to my US friends , : when delegating separation VFR to an aircraft does that automatically cancels its previous altitude restrictions ?
(*) I mean control input to maintain visual separation . not last second collision avoidance maneuver.

A Class B tower is a different animal than a Class D that might not even have a radar repeater of any kind.

Subjects ATC FAA ICAO Radar Separation (ALL) VFR Visual Separation

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henra
February 03, 2025, 18:43:00 GMT
permalink Post: 11820790

Quote:

Originally Posted by YRP

Either way, the controller does not have enough information to use a heading — neither to know one is needed nor what it should be . The radar & display is just not as accurate as a Mark I eyeball in one cockpit seeing the other plane out the window.

Hmmm. Dunno. Would you really expect this maneuver to be executed in such proximity that it can't be reliably resolved by the radar accuracy? At night? In a 45\xb0 head- on angle of the two flight paths? Your comfort zone for sure is a different one than mine would be.

Subjects ATC Radar

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JohnDixson
February 03, 2025, 19:05:00 GMT
permalink Post: 11820804

From the FAA website:\x93When Radar Came to Town

On January 7, 1952, after five years of testing and modifications to a radar system used

by the Army and Navy in World War II, the Civil Aeronautics Administration

inaugurated radar departure control procedures at its Washington National Airport. Six

months later it began radar approach control procedures at the airport.\x94

How do we connect the dots from 1952 to the tragedy described in this thread? 72 years later we have devolved to visual separation.

Subjects FAA Radar Separation (ALL) Visual Separation

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jumpseater
February 03, 2025, 20:07:00 GMT
permalink Post: 11820853

Quote:

Originally Posted by West Coast

I used to many moons ago as a controller when working local in both class B and C airspace.

Did you have, or need a radar based qualification to do that?

A UK Tower/LC can\x92t give headings unless they are radar qualified and current, and have the appropriate equipment.

Subjects ATC Radar

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ATC Watcher
February 03, 2025, 20:19:00 GMT
permalink Post: 11820865

Quote:

Originally Posted by JohnDixson

From the FAA website:“When Radar Came to Town

On January 7, 1952, after five years of testing and modifications to a radar system used

by the Army and Navy in World War II, the Civil Aeronautics Administration

inaugurated radar departure control procedures at its Washington National Airport. Six

months later it began radar approach control procedures at the airport.”

How do we connect the dots from 1952 to the tragedy described in this thread? 72 years later we have devolved to visual separation.

indeed, Indeed . interesting to remember where it all comes from and having the first collision this century coming back in the same airport they introduced APP radar over 70 years ago while doing a visual approach a night following a PAPI .
But remember , here the APP radar controllers with the proper ratings and radar tools ( including Conflict alerts) are not in the TWR cab in DC, , they are located in Potomac TRACON , another town , in Warrenton , Virginia ,

.

Quote:

Jumseater
A UK Tower/LC can’t give headings unless they are radar qualified and current, and have the appropriate equipment.

Correct , Same in EASA land. in addition in FAA web site DC TWR is classified as TWR only .

Last edited by ATC Watcher; 3rd February 2025 at 20:24 . Reason: adding comment to jumpseater post

Subjects FAA Radar Separation (ALL) Visual Separation

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MPN11
February 03, 2025, 20:22:00 GMT
permalink Post: 11820868

Quote:

Originally Posted by jumpseater

Did you have, or need a radar based qualification to do that?

A UK Tower/LC can’t give headings unless they are radar qualified and current, and have the appropriate equipment.

That is a question I posed way back. Does DCA Tower have a slaved radar display? Does a non-trained/qualified controller have the authority to use that data in extremis? Personally, as an ATCO, and presented with imminently co-altitude and virtually head-on conflicting traffic, I would have intervened. But then I was always an interventionist Tower controller!

My earlier questions remain unanswered … does DCA Tower have a slaved radar display ?
And thus could Tower have used that data to direct PAT21 out of the way, regardless of qualification or licensing? Or did Tower have a Radar qualification anyway, but didn’t use it?

Subjects ATC ATCO DCA Radar

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ATC Watcher
February 03, 2025, 21:07:00 GMT
permalink Post: 11820895

Quote:

Originally Posted by MPN11

That is a question I posed way back. Does DCA Tower have a slaved radar display?

I do not know , what kind and how it is used. Some US controllers said in another forum they now have one , but what is it , where it is located and what the procedures are I do not know. Normally at large airports you have a radar picture repeater for situation awareness not for providing radar control unless you are in a TWR-APP combined facility of course , but DC is not.
and

Quote:

Does a non-trained/qualified controller have the authority to use that data in extremis?

if you mean in emergency , to prevent a collision ? , yes absolutely because in legal terms you always have the duty of care That is what the judge will come back to in the end. Now that said, where was the display located ? remember the guy was working 2 positions at same time . If there was a radar repeater display somewhere , was it located at the position he was working from ? The NTSB investigation will tell us that
.
If you are a controller you know how we work , Problem identified , = Conflict with PT detected , solution found = delegate separation , delegation accepted = problem solved. Next ... The guy was quite busy with departing and arrival traffic in runway one . Now of course with hindsight ,, what he should, and could perhaps have done is very easy for us to say . Feel very sorry for the guy . I hope he is not made the scapegoat for this mess.

Subjects ATC DCA NTSB Radar Separation (ALL)

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JRBarrett
February 03, 2025, 21:44:00 GMT
permalink Post: 11820928

Quote:

Originally Posted by MPN11

That is a question I posed way back. Does DCA Tower have a slaved radar display? Does a non-trained/qualified controller have the authority to use that data in extremis? Personally, as an ATCO, and presented with imminently co-altitude and virtually head-on conflicting traffic, I would have intervened. But then I was always an interventionist Tower controller!

My earlier questions remain unanswered \x85 does DCA Tower have a slaved radar display ?
And thus could Tower have used that data to direct PAT21 out of the way, regardless of qualification or licensing? Or did Tower have a Radar qualification anyway, but didn\x92t use it?

I can\x92t speak for DCA, but my local Class D airport (KELM) has had a radar repeater in the tower cab since the late 1980s, and all the local controllers use it. I would think DCA almost certainly has one. The radar repeater is not used to give vectors to aircraft, but as an aid to the controller\x92s situational awareness.

Subjects ATC ATCO DCA Radar Situational Awareness

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YRP
February 03, 2025, 22:45:00 GMT
permalink Post: 11820974

Quote:

Originally Posted by Undertow

Potomac Approach is not in the same building (or at least room) as the Tower controller.

He\x92s asking the reason to find out what the a/c wants: sequence for another approach, divert due weather, hold to work out a technical fault.

Tower could have passed it on the hotline but it is probably normally more efficient to just have the a/c say.

Working about the safety implication of why the RA and what it says about the procedure is not something for the radio.

Subjects ATC Radar Republic Airways Flight 4514 Go-around

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