Posts about: "Pass Behind" [Posts: 111 Page: 6 of 6]¶

Hi MechEng , it's been a while since it was discussed.

Here is the NTSB report/transcript and another transcript here . I couldn't locate the one on Prune way, way back but these 2 will do!). ATC specifically call the a/c sidestepping to 33 as the a/c PAT needs to identify. The ATCO even tells PAT what type it is. PAT then say they have "it" visual. Sadly, "it" wasn't the sidestepping a/c, it was another one. But no-one figured that out ...... till seconds before the crash. This initial exchange, according to the transcript, was about 2 min before the collision. It's only then, on the basis that PAT says they have seen "it" and, by implication, will visually avoid it, that ATC issue the clearance on down Route 4.

There was a lot of discussion earlier on in this Thread about how on earth PAT could be reliably expected to pick out the subject a/c from the rest of the stream of arrivals and at that distance (6 miles rings a bell).

It's only seconds before the crash that it appears that the poor ATCO suddenly starts to suspect the PAT crew are actually looking at a different a/c to the one he had asked them to identify and pass behind. But, by then, it was too late for him to figure out a solution to give to PAT.

As I said, this was all discussed many posts ago so it's easy to forget the details. Hope the links help!

Cheers, H 'n' H

ATCDumbo
I'm all ears, excellent point. This focus on ADSB-OUT, and ADSB-IN is really a furphy in terms of this investigation to determine the facts, the whole facts and nothing but the facts.

If 5342 had ADSB-IN then PAT25 not having or not displaying ADSB-OUT could be relevant depending on 5342's cockpit display, the training of the pilots and their scanning.
5342 didn't have ADSB-IN so move along, move along, nothing to see, these aren't the droids you're looking for.

**Caveat. If the TWR display were using ADS-B for their updates and to generate Collision Alerts then the absence of PAT25 ADSB-OUT could be relevant.
But would the TWR ATC even know (or care) whether PAT-25 was ADSB-OUT capable. TWR ATC involves looking out the windows and judging the relative positions of aircraft.

Note: ATC display systems are not referenced in the NTSB Aviation Investigation Preliminary Report. This seems to be a glaring omission. So perhaps the NTSB are either very dumb or deceitful or both.

To further illustrate the focus on ADSB. Figure 1 Google Earth image with preliminary ADS-B data for flight 5342 and radar data for PAT25.
The ADS-B plots are 1 seconds intervals, the radar data are 4 second interval (as stated during US Congress Q&A).
So the focus is on the whizz bang ADS-B kit rather than what the ATC saw on their display.

There is reference to ATC radios, and 5342 was on frequency 119.1 MHZ and PAT25 was on frequency 134.35 MHZ. The ATC could've had them on the same frequency (changed PAT25 to 119.1 MHZ) but this would be abnormal. ATC Voice Switch systems like Frequentis, SITTI and Rohde & Schwarz typically have a frequency coupling, whereby controller broadcasts on multiple frequencies (2 or more) and voice communications on one frequency are heard on the other. In this case, ATC would broadcast on 119.1 MHZ and 134.55 MHZ and 5342 would hear instructions for aircraft on 134.55 MHZ, and PAT25 would hear instructions for aircraft on 119.1 MHZ.

Yes, visual separation is typically used close to an aerodrome where the ATC is applying visual separation to reduce the standard from 3NM to something less, 2NM, 1NM, or even less, depending on the circumstance which includes weather (included visibility), day / night, workload to monitor the separation, plus other considerations such as equipment.

I just wonder how many of the January Route 4 Helicopter plots crossing RWY 33 Approach (post 1346) were the result of ATC issuing a control instruction to change the track to closer to the shoreline or further over water.

Use of Route 4 during RWY 33 Approaches or RWY 15 Departures is possible providing a clearance limit is imposed prior to assigning relevant traffic, positive control instruction(s) and in the case of 5342, advising them of the relative position of PAT25 and that PAT25 would be maintaining separation from them.

Example for Route 4 southbound would be a clearance limit of Hains Point. Helicopter would be released past this point when there is no conflict (nil traffic) or assigned separation to avoid (pass behind). If there is a in-line stream of arriving traffic then Route 4 may not be available.

Sydney KSA has something similar for one of their helicopter routes - BONDI 5 (yep, named after the beach), delays may occur when RWY 07 is in use for DEP, or RWY 25 is in use for ARR. Further, the route is not available when RWY 16 PRM approaches are being conducted. Sydney KSA helicopter routes are in text form - TRACK TO..., TRACK VIA..., EAST OF..., and the INBOUND routes to Sydney KSA have a clearance limit in the clearance. A map display is very useful however it should be based on route descriptions. Perhaps the committee of 17 knows the history of the helicopter routes in and around DCA.

Although the data in post 1346 does distinguish between day time and night time, it doesn't (nor probably can't) highlight which flights were adjusted by ATC, e.g. track this, sight that, pass behind, track direct, etc. If the use of Route 4 was simply pilots doing their own thing ie a single direction route without any ATC inputs then the tracking difference might be interesting. In this case, it could highlight an issue, perhaps not.

I have flown that route a handful of times during my time in the Marine Corps (admittedly it's been more than 20 years ago). I recall being asked to do a 360 turn over the Wilson Bridge for spacing (we were northbound) for traffic landing on 33.

In regards to your other comment about them not seeing the CRJ, I have believed from the time that the radio traffic was public that the controller was not specific enough when he asked PAT 25 "do you have the CRJ in sight?" Something along the lines of "PAT 25, CRJ on final for RWY 33 is at your 10 o'clock less than a mile, pass behind that traffic" should have drawn the helo crews eyes to the left to hopefully see the traffic. Even better would have been to have the helo do a left 360 over Hains Point.

@ Sailvi767 : Are you suggesting that somehow the CRJ crew bears some responsibility in not acting on a TA and therefore bears some responsibility in this accident ? At least this is what I am making of your posting .
If I am correct can you stop this discussion Remember journalists and possibly families members of those 2 pilots are watching too.
To close that bit just read the CRJ CVR transcript (*)
47:29 : eGPWS : 500 hundred
47:35 : I got 2 whites and 2 red
47:37 : cool ( my note : so they were looking at the PAPI )
47::40 : "Traffic traffic " ( my note : TA audio)
47:47 : TWR :" PAT 25 pass behind the CRJ "
47:55 : eGPWS : ...hundred ..
47:58 " Oh Sh!!!!!
47:59 : sound of impact .

As I posted on here before I had that exact same scenario happen to me on runway 33 in DCA. Traffic closing on a collision course on TCAS. Tower reported the traffic had us in sight. When the traffic closed to \xbd mile with no vector change apparent We went around from 400 feet. We never saw the traffic. Tower chewed my butt saying the traffic had us in sight. I didn\x92t care.

But he kind of did issue it : 20:47:42.0 TWR- (LC): " PAT two five pass behind the C-R-J " . [[i]sounds of rapid beeping consistent with conflict alert audible in background while tower is transmitting]
17 seconds before the collision , sadly he did not receive a clear readback on that instruction .

Yes he did, you\x92re right\x97 but it wasn\x92t proactive enough. Clearly the LC was conflicted, his eyes telling him PAT might not be visual, but the pilot saying he was. What an awful situation to be in. One which really needed a decisive move, not the easiest one, eg order a direct turn for PAT and/or a go around for the CRJ.

yes, but the local controller transmitted on both, e.g. the message where the controller told the Blackhawk to pass behind the CRJ.

None. That would obviously be unsafe, so the helicopter would be expected to use lateral separation. (e.g. "Pass behind the CRJ.")

The 200 ft altitude restriction seems to have given some the impression that helicopters were routinely passing directly below the approach traffic, but that's not the case. And even if it was, it wouldn't really be relevant to this accident. The Blackhawk pilots weren't trying to duck underneath the plane, they never even saw it.

You mean no SA was made because this scenario was not even considered ? That makes things worse for the FAA if this local "visual " procedure was written down somewhere or even just tolerated , because as I understood, it was standard practice .I am not sure if you know how safety assessments are made , but you must consider every possible scenario when designing procedures.


From a European / EASA perspective :
Re the "Lateral separation" you mention : in that scenario so close to the Runway threshold it would mean only a left turn is possible, i.e. away from the thresholds of both runways , it would mean flying over build up areas , and doing so at 200ft above buildings with possible antennas on top , etc.. ,not really safe , and definitively not at night . As to \x93pass behind\x94 , the standard wake turbulence separation criteria would not be met , especially passing behind/below and I would not even try that at 200ft under a large jet..

So , applying standard safety assessment criteria , allowing visual separation to aircraft on that route, even less at night where danger of mis identification is increased . would definitively not be considered \x93 Safe\x94 .

During the interviews, one Heli pilot from that same group ,mentioned that asking for visual separation was a routine request , even if you did not see the traffic at time of the request . That fact alone, if really proven to be systematically the case , would also add to the normalization of deviance case and put full responsibility on the regulator, not the pilots