Posts about: "INLINE_IMAGES" [Posts: 88 Page: 2 of 5]¶

Altitudes 2 and 4 seconds before the crash and then just both flip to 3.

In addition to previous post on the differences of TA & RA's (which were inhibited at that moment), No they were not left 'out of the loop', but they use their TCAS displayed info, as much as you use your Flarm display when on short final.
From the 'Mil' thread:

I turn the collision alarm off on my boat in the harbor, I am always aimed at someone if I kept going in a straight line and the noise would drive me nuts. What I leave on is the CPA display. If that dashed line keeps shrinking, I have a problem. Granted this display is optimized for much slower moving targets, but something similar could be done for the helicopter fleet with ADS-B. It would have clearly shown the helo was closing in on the aircraft, not flying behind it and also would have shown they might not even be looking at the correct one. Not shown is I can pop up a box on the target that shows me CPA and time to that CPA. I can also set the parameters that turn targets from green to red.

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.

The pinkish coloured mark in the lower middle of this screenshot is the splash of the Blackhawk hitting the water.



It's at about 31 seconds into this video

Unlikely. The helicopter crew was told about the CRJ approaching 33. At the moment of that initial traffic advisory it meant, the CRJ would first cross their flight path from right to left, and then later on final (circle to land) from left to right. Did they simply expect still the former, seeing the second jet approaching 01, misjudging the timing / distance as to the CRJ, and therefore turning right to pass behind / give way to an approaching aircraft espected to turn any moment and cross their path from right to left?

If people (and even 'reliable Youtubers') would stick to the available facts, instead of complicating things
No crossing of 'Route 4' prior to ...

VHF, UHF, .... the important fact is that pilots were on different frequencies...whatever spectrum band they were on, is less relevant.

But for those rebuking any mentioning of a VHF Heli frequency, please provide some proof as any reference I find on VFR sectionals, is a VHF Heli-frequency.
IFR charts only have the regular VHF+UHF TWR freq.

Still, if the helo crew misidentified the A319 as the CRJ, and they assumed the A319 will start turning right soon to circle for 33, turning right as well would have increased horizontal separation. And the extended centerline for 01, which the A319 was aligning with, does actually intersect with Route 4 a bit after the Wilson Bridge. And, looking at the radar replay, the A319 did actually turn right for a bit, to align to 01. At around the same time, the helo starts turning right.


I agree that these are just guesses, but the alternative seems to be that the helo just drifted to the right randomly, for no specific reason, which seems unlikely.

Well I only replied to the CRJ not crossing "Route 4" as some people paint on screenshots...

the A319 was adjusting a few degrees left and right, but wouldn't call that 'turning' (but of course its position would make it an ideal target for misidentification)



Well, it's probably my worn out eyes, but I don't see really any reliable evidence of the helo turning right ... remember it came out of Route 1 which ends in one big right-hand turn until joining Route 4 which only after passing KDCA airfield, has a very slight course adjustment to the left.

And the "amateur MLAT" tracking of the helo, is only a rough indication of the trajectory with a wide margin of position error and should be interpreted more like the right side hereunder:

The radar video from AV Herald seems to be a recording of the actual radar display, not "amateur MLAT". Of course, without an overlay with the map and the routes it's a bit hard to say how much the helo deviated from its route. I tried to create such an overlay, but I can't vouch for its accuracy:



And yeah, with the route overlayed on the radar, the deviation from the route doesn't seem to be that great, since the route itself also turns right.

so that we are all on the same page:

matching the info from the NTSB transcript briefing to the ADS-B trajectory:

exactly at 500ft it seems
to put "all the way" into context, 18 seconds is what they had

What is your source for the G/S? According to the surreptitiously recorded radar display, the helicopter ground speed appears to be closer to 80 kts.

apologies, I may have misheard it somewhere.

I think we can take this (radar recorded) data-source as pretty reliable, it matches (rounded) the ADS-B reported CRJ speed of 121kts at 375ft (QNE)

I think the confusion comes from the "amateur MLAT" tracking, which calculates the GS based on the multilaterated position calculations, which have a (relatively) large margin of error:


And probably PAT25 was doing initially something in the region of 100kts GS (edit: averaging all but last calculated GS, gives 105kts as average - and over more datapoints, longer trajectory, calculated average GS becomes more reliable)

but at the end it seems there might possibly have been a decreasing GS trend:

Just for illustration, this is how it's done in London (or was some time ago last time I did this sort of work). Accurate compliance with routes is strictly enforced and clearances are SVFR day and night unless this has changed. Almost invariably clearance to enter would state the route/s ie 'H4 H3 Bagshot Mast' (straight through) and no other instruction required - that takes you E -W right through the centre of London and out to the W passing 5 miles S of Heathrow. Right hand rule applies and opposing traffic on the route is always advised.
Usually, only if crossing LHR you'd be cleared to enter via requested route with limit Bedfont/Sipson, sometimes Airport Spur to hold (orbit) and change from Heathrow Special to Tower for the crossing itself. There's a further hold at Twin Taxiways between the runways. Altitudes are shown. Note there is usually unrestricted passage on routes H3 and H10 along the river directly under the approach. This system works seamlessly and with - to date - total safety.
Accepted the aairport we are discussing has more varied runway directions than Heathrow so the situation would be a bit more complex but I can't see why a similar system couldn't be devised - with defined clearance limits, sensible vertical separation and, critically, coherent and specific controller voice procedure.

There's no reason not to make landing traffic aware of helos holding close in if appropriate and indeed that happens, but no way is their visual contact required.
The entire system operates on visual 'separation'. Helos cross visually behind traffic as cleared, but with vertical separation. It's as safe as the system can be made. How else could it work? It requires no controller vectoring and the time and space margins that would be required if radar separation was used would render the slick, efficient visual system cumbrous, unacceptably high end unnecessary workload and probably unworkable.
Please, once again let's stop applying this insular f/w procedural IFR mindset to VFR helo traffic. There seems to be a procedural IFR mental blockage that can't see that 'visual separation' occurs in three dimensions, not just two. Helos are perfectly capable of ensuring visual separation as long as the traffic has been correctly identified and with vertical separation as here even if a mistake is made there is 800ft clear vertically. Also, VFR does NOT mean, as many seem to imagine, blundering about randomly at will, it is often every bit as disciplined and controlled as IFR as Shackman reiterates below, these routes are rigidly enforced to within a hundred metres or so and woe betide the transgressor.

The elephant in the room here is a combintion of a ridiculously hazardous two-dimensional crossing procedure combined with culpably sloppy & imprecise r/t which offers no second slice of cheese, not matters of visual separation. I'm well aware that our transatlantic cousins are sensitive to criticism of their relaxed, easygoing and informal ways in the air but in this case they self-evidently were the direct cause of 70 odd deaths. While they may regard European style as excessively pedantic there's no doubt whatsoever that had European standards applied here this event would have resulted in nothing more serious than a MOR and an Airmiss report.

For those unfamiliar the light grid squares are 1Km so the Sipson and Bedfont reporting/holding points is ony about 500m from the runways.

I don't think it make a significant turn right, and I believe that what you are seeing is positional inaccuracy due to MLAT position limitations in the ADS-B Exchange data. According to Flightradar24, " MLAT position calculations have a general accuracy of 10-100 meters and 1000 meters in the worst cases." Given that, I believe this previous post from MikeSnow AA5342 Down DCA represents our best current understanding of the actual helicopter track and its relation to Route 4 (until we get more information from the NTSB). I generated my own zoomed overlay and got essentially the same results



The position of the collision shown in the radar data overlay is consistent with the position of the RJ as shown in ADS-B Exchange at the time of the collision (approximately 01:47:59Z according to the NTSB timeline). See this link from DIBO for the RJ Track with timing AA5342 Down DCA In my experience, times in ADS-B Exchange are generally accurate to within 2 seconds. Given all that, I believe that the Black Hawk was within the horizontal bounds of Route 4 at the time of the collision and that it did not make the right turn we see in the ADS-B Exchange map.

Edit: Corrected route number and helicopter

Had there been a fourth crew member in the Blackhawk, which routinely would have been seated on the port side with a view in the direction the CRJ was approaching the helicopter....you reckon there might have been a possibility that might have allowed for the sighting of the CRJ and thus prevent the collision?

Owing to the vision limitations caused by use of NVG's it is not out of the realm of consideration Army policy would require for two crew members in the rear of the aircraft to enhance conflict resolution.

We routinely flew Chinooks with three crew in the rear with two designated to watch for traffic on either side of the aircraft. The third crew member was the Flight Engineer who controlled activities in the rear and performed safety checks. That simple concept saved my Bacon more than a few times.

NYT has attempted a reconstruction of the visual picture from the Blackhawk at the time of the first traffic alert, with the CRJ just south of Wilson Bridge.
They could only later identify the correct light spot by following its trajectory according to their mental image of the approach to 33.