Posts about: "Vertical Separation" [Posts: 73 Page: 1 of 4]¶

I was talking about visual separation; I should have been clearer.

Might have helped the CRJ see the helicopter (except a military helicopter probably won't be illuminated anyway). But if the helicopter crew has CRJ landing lights pointing at them, are they going to see anything? It seems like another poor-quality band-aid on top of the fundamental problem of trusting see-and-avoid and voice comms.

RVSM is 1000ft at higher altitudes; even if things had gone 100% to plan, this would have only provided, what, <300ft vertical separation? Is wake turbulence a threat to helicopters?

Heli route 4 is at or below 200ft if I read the chart correctly.

Approach traffic seems to be approx 400-500ft at this point.

Which turnip decided it would be OK to allow vertical separation of 300ft on a busy approach path? And allow it VFR at night?

This accident was baked in. Bound to happen at some point.

But it's worse than that. The approaches to DCA are only moderately complicated; however, unlike most airports, DCA is surrounded with frustrated people just waiting to call the FAA if you deviate from the published procedure by the slightest amount. Nobody want's to do a rug-dance in the Chief Pilot's office because some Senator's aide gets his/her panties in a wad, or worse, get a violation from the FAA because you flew over someone working for the Secretary of Transportation. I always enjoyed flying in and out of DCA because it was challanging, but I was always on my toes, constantly checking my altitude, position (both visually and via instruments), airspeed, etc. because it is so easy to get your teat in the wringer at DCA.
In this case, the aircraft was flying an approach to one runway with a circle-to-land on RW-33. Ask any pilot; a circle to land in itself ups the work load. The margin for error of any kind at DCA is small and the 5200 foot runway isn't all that long. Even on a simple landing where none of these considerations are an issue, at some point the pilots reduce their "see and avoid" efforts and concentrate their efforts on achieving the proper line up and glide slope, rate of descent, aircraft configuration, flap setting, etc. etc. etc. In other words, the complicated routine required to safely land an airliner these days is already close to task overload even when things are going well. Add in the fact that it's night time at a very busy airport and looking out the window gets shoved pretty far down the "to do" list. But generally speaking, the system works because big busy airports pretty much operate using IFR rules and nearly all the aircraft are under close control. I other words, even on a crystal clear day under VFR flight conditions, someone is keeping a very close eye on the airliners coming and going from major airports. If a pilot makes a mistake and levels off at the wrong altitude, for example, there is a very good chance a controller will catch that error immediately even on a sunny VFR day. And that's a good thing because truth-be-told, when an airliner is seconds from touch down these days, there isn't much "see and avoid" going on. That's just the way it is.

But apparently DCA routinely has all sorts of helo traffic buzzing around under modified VFR flight rules. The pilots are talking to a controller but without being under the same sort of close control which is usually associated with how airliners operate. And they do that night and day, trusting the helo pilots to not make a mistake. But it looks like someone DID make a mistake last night and nobody caught it in time.

When and where I learned to fly (and on each new rating, refresher and check ride) we had to prove that we knew airspace classification. DCA is listed as class B airspace (and special rules on top).
That should apply worldwide, not just in EASA land.
It seems to be a US speciality that ATC can delegate the separation to aircrews (visually) and this at night! And how the hell can ATC separate vertically near the ground when mode S transponders report pressure altitude in steps of 100 feet only?
I dont know the rules of vertical separation by heart but its certainly not less than 500 feet for crossing paths. Is one last digit more or less a separation? This heli crew should have been told by ATC to hold until the aircraft(s) on final have safely passed. It's one of the benefits of a helicopter that it can hover.

If that published in AIP route 4 crossing under the final approach path of RWY 33 says max 200 ft and according the calculations made by Luc Lion earlier the altitude of the CRJ was, if not exactly on the PAPI , very close to it at 300 Ft in less than a mile before TDZ. But 100 ft separation is not a normal civil vertical separation standard in controlled airspace, for an IFR flight. it is 500 ft minimum in our books. . One of the roots of the problem is right there : a published route where you need a visual military type separation to make it work . And it may have worked hundreds of times before , sometimes with luck I am sure, but this time it did not and this was just an accident waiting to happen written in the book.

To answer an earlier question , Yes they have CISM , NATCA is good at this , they will take care of the controllers.

@ fdr : our posts crossed each other , fully agree with you .

See and avoid in airline operations simply does not work. High workload, human factors, visual limitations, high closing speeds simply make it unreliable.

There have been countless similar cases of near misses. Near airports, crossing traffic, especially helicopters is a real issue, as is the totally inappropriate see and avoid principle with commercial traffic. In my view we need a complete rule change and rethink around lack of radar separation between IFR and VFR traffic.

All too frequently ATC allow IFR and VFR far too close on approach and are permitted to just inform the VFR traffic to visually manoeuvre themselves all too close to IFR traffic. The book 'The Naked Pilot' years ago established that see and avoid does not work, simple as that.

Class D airspace whilst not necessarily involved here often causes such issues. Pilot's wrongly believe ATC separates IFR and VFR. Frequently ATC allow conflicts to develop on the basis of law, rather than duty of care. We need to get back to common sense, and that is ATC must stop VFR traffic getting anywhere near airliners on final approach or from crossing the go around track. Either lateral or vertical separation needs to be enforced or repeats of this type of accident will definitely repeat.

Lessons have not been learned previous to this accident. I fear we will see a repeat, and low level near airport ATC separation needs to improve.

We need the industry to wake up and realise, see and avoid is unreliable, and air law does not protect IFR traffic from VFR traffic enough.

Interesting viewpoint.
My take is, in order.
5) No, I don't think he was overwhelmed. He was shot through with adrenaline and shocked as anyone would be having just witnessed two aircraft he was talking to seconds before vanish in a fireball, realising his career, reputation, life and future sanity was irrevocably blown to pieces no matter the cause.
No, no and thrice no. Assuming the tapes are in real time there are considerable gaps between transmissions so he most certainly did not 'have' to speak so quickly. He had plenty of time to speak clearly and coherently instead of spouting those eruptions of incoherent, almost incomprehensible babble.
Sadly - reprehensibly, this style of unnecessarily theatrical auctioneer-style unpunctuated babble seems all too frequent in the States. Tower frequencies are usually if not almost invariably much less time-pressurised as they handle fewer aircraft in a well spaced sequence than in a termnal control area.

6) Concur 100%. And they failed miserably to achieve this. I've been flying for several decades and struggle to hear one word in three (and only assume much of the rest because I know what to expect - a human factors disaster) of that controller's outbursts, and the shoddy partial readbacks are shocking to European ears.

7) Once again, NO! Even if super-busy (and I'd argue especially if super busy) it is essential to keep r/t steady, clear and comprehensible; gabbling that fast might save half a second on an exchange, but no frequency is so busy it requires that, least of all a Tower. He only had three or four aircraft to deal with for simple go-arounds, all well spaced out on approach. He pretty much had time to recite half the Lord's Prayer to each.

This crazy r/t seems to be a cultural thing and needs to be changed, as do some fundamental procedures like having helo lanes crossing final approach tracks at essentially the same height instead of with decent vertical separation. Why wasn't the helilane at 800ft or 1000ft as a Heathrow? No aircraft is up there one mile out from finals while every single one is at 300ft. Madness. Just madness. It's like a figure 8 banger race dodging cars at the intersection. If there was a flyover - vertical separation too accidents would be all but eliminated.

And this buisness of "...pass behind the CRJ on finals" when no none can determine whether the lights in sight are a CRJ, a Cessna or the Space Shuttle or in what sequence they are landing. It might work in daylight but imho it assumes unreasonable levels of instant almost head-on aircraft recognition - a disastrous human factors trap quite aside from the additional one of assumption.

I'm not having a go at the poor controller who imho is compleely blameless, he did his job as well as the flawed system that indoctrinated him allowed.

As for 'stopping' helicopters in a free- air hover. This is (in my experience) never ever requested, done or attempted as a traffic avoidance method. I can only assume people suggesting this have absolutely zero knowlege of flying helos and the litany of pitfalls and hazards it would generate, helos simply do not 'stop' in midair unless they have to for SAR, load-lfting ot maybe surveillance. If necessary, as in holding at 'dual taxiways' between the Heathrow runways at 1000ft you'd slow to a sensible speed, maybe 50-60Kts in a tight orbit and even that is 'interesting' in 40Kts of wind. "Are you visual with landing traffic 2 mile final" identifies the traffic far, far better than "the CRJ on finals" when there might be three in a row, not to mention assuming superhuman powers of head-on distant aircraft recognition even in daylight - and impossible at night!!! Crossing clearance is then "cross over the threshold after the landing traffic" where no aeroplane ever is at 1000ft. (bar a g/a when there is enough time to skedaddle and avoid) With any significant wind a hover would have to be into wind, ie more or less tail -on to the conflicting traffic, an utterly absurd concept. Bin this one people, please.

As for the appalling behaviour of the 'president' to instantly apportion blame with no understanding of either the situation or accident investigation in general whatsoever - which anyway is not his job and none of his business, thereby prejudicing any enquiry (what pressure does this put on the investigators and report writers, federal employees, when they are all but directed by their deranged and vindictive boss what they are expected to report? This is a very, very dangerous precedent that smacks more of a shonky third world dictatorship than a western democracy.

It is really like that? Yes, I have seen the map but honestly I don't know how it works in real life. Do they really just fly bellow aircraft on final with vertical separation like 100-200 ft or they have to avoid them, let's say cross behind. What is too close in this case?

The only logical explanation I can come up with here is the last second runway change caused them to be a lot closer than originally thought. Pretending I haven't seen helicopters all over the place for decades now around here and thinking as a newcomer, this sounds bat-s##t crazy, like an airshow stunt, to have traffic crossing like that with a helo ducking under an airplane on short final.

That's what I'm also wondering. And assuming a standard 3\xb0 glideslope the vertical separation at that point would be even rather less than 100ft. I can't really fathom crossing 50-100ft above the whirly bits of a Blackhawk being a regularly executed standard procedure !? What is the 'normal' way of doing this in DCA?

This procedure was not for sure designed so that the vertical separation is only separation, no, horizontal separation is supposed to be the way you do it. Separation is anyway based on visual avoidance in dark, not good! Anyway the HELO was zick zacking, not following the route 1 and 4, and did not maintain altitude, why was that?

30 seconds before the collision, when LC asked if they have traffic in sight, HELO was on track about 200\xb0, because of wind (320/25) HDG was somerhing like 215\xb0. Bearing to CRJ was 10 o’clock and to A319 about 11 o’clock. At this moment CRJ was flying track to North, base for rwy 33, and was not at all conflicting traffic from HELO’s point of view. Few seconds later HELO turned to the South, perhaps to avoid A319, soon after noticed that A319 will pass far ahead and turned back to right… so sad.

I am not a USA airspace expert, and I'm sure there are many rules that I don't know about, but having just read the FAR AIM section on 'pilot-applied visual separation' it reads to me, as an interested foreigner, that the LC can pass responsibility for separation to a pilot if they are visual. The class B separation criteria states:

VFR aircraft must be separated from VFR/IFR aircraft/ helicopter/rotorcraft that weigh more than 19,000 pounds and turbojets by no less than:

1. 1 \xbd miles separation, or
2. 500 feet vertical separation, or
3. Visual separation, as specified in paragraph  7-2-1 , Visual Separation, paragraph  7-4-2 , Vectors for Visual Approach, and paragraph 7-6-7 , Sequencing.

The rules for pilot-applied visual separation state:

1. If the aircraft are on converging courses, inform the other aircraft of the traffic and that visual separation is being applied.
2. Advise the pilots if the radar targets appear likely to merge.

Whilst I agree giving avoidance instructions would possibly be a sensible thing to do, I can't see that explicitly written in the FAR AIM if pilot-applied visual separation has been approved. There may be other sections (or other regulations) that go into more detail that I am not aware of.

Thanks, indeed from the ATC transcripts published online so far, it doesn\x92t transpire that LC, after the helo (re-) confirmed being visible with the CRJ, complied with the following:\x93NOTE-

1. If aircraft are on converging courses, inform the other aircraft of the traffic and that visual separation is being applied.

PHRASEOLOGY-

(ACID), TRAFFIC, (clock position and distance), (direction) BOUND, (type of aircraft), HAS YOU IN SIGHT AND WILL MAINTAIN VISUAL SEPARATION.

1. Advise the pilots if the targets appear likely to merge.

NOTE-

Issue this advisory in conjunction with the instruction to maintain visual separation, the advisory to the other aircraft of the converging course, or thereafter if the controller subsequently becomes aware that the targets are merging.\x94

Because it\x92s sometimes the best place to cross helicopter traffic through the final approach path.
Note I say \x91through\x92 and not \x91under\x92.

I\x92m sure it is done at many airports around the World and we have a similar procedure at a large international airport in East Asia.

HOWEVER, the idea that the 200ft ceiling on the heli route is designed to provide vertical separation from the approach is ludicrous.

I suspect that limit is imposed to allow clearance from the Take-off climb surface if using the opposite direction runways. That would indeed be possible from a flight procedure design point of view (TERPS or PANS-OPS).

The only safe way is to cross behind traffic on final laterally . In some ways it would be better for the heli to be at a higher altitude if on 33 but for simplicity of procedure they may have just made it a blanket 200ft regardless.

Our procedure has laterally separated holding points either side of final which is the clearance limit where the heli can orbit or delay as necessary until confirming the aircraft to pass behind is in sight. The heli is also advised where the next aircraft in the sequence is to further verify the correct aircraft is in sight and what margin they need to leave behind the one crossing behind. Again, being higher is better as they can avoid wake turbulence by remaining well an above the glide path and pass closer behind, well ahead of the following.
There is no doubt night time makes this a far more critical operation and requires full attention. In our operation the heli is also on the same frequency as the approach aircraft, so having separate positions to control fixed wing and helis wouldn\x92t have any benefit.
This controller was hugely busy however, handling departures as well. I can\x92t believe the speed of his transmissions - even as a controller for over 30 years I have trouble with all the abbreviated phrases- of course local pilots would be used to it and expecting clipped frequencies etc\x85

The trouble with a lot of these types of procedures is a lot is carried out as a box ticking exercise - heli calls requesting to cross the final ✅, LC provides the position of the aircraft to pass behind ✅, heli reports sighting and requests own visual separation ✅, approved ✅.
LC is no doubt expected to monitor compliance visually although hugely busy with other traffic on the runway. It does sound like he was doing so, especially when the CA goes off in the background audio and puts doubt in his mind the heli is passing clear of the CRJ. He asks again immediately.
The heli confirms, so difficult to further challenge the pilot.

In my view a poorly designed procedure which was guaranteed to place the 2 aircraft in the same position if an error was made.

I just can't see that ATCduty peresonnel have any fault in this (apart from habitually lousy r/t). They did their thing correctly according to the procedures they were expected to work with.
The accident appears, almost certainly, to have been directly caused by the misidentification of conflicting traffic by the helo.
Fundamentally though the accident was entirely set up and enabled by critical faults in airspace usage and procedures, viz no vertical separation betwen the helo lane and glideslope at their point of intersection (to my mind simply incredible) and to a lesser extent perhaps the (again to my mind) extraordinary split frequency system. The first provides only one slice of swiss cheese - substantial vertical separation would add a second slice while the frequency thing is no cheese at all.

Despite what some commentators here and elsewhere seem to think there is never intended to be a situation when a helo passes under an aircraft on finals at 200ft. Helo traffic is held, or holds itself following a conditional clearance short of runway track before proceeding visually behind landing traffic or ahead of traffic on longer finals, exactly as is done at Heathrow. The difference is that in the event of an error at LHR there is 1000ft of vertical separation to add guartanteed separation if a helo wanders off track. Here there is next to none, it is very like a road intersection where cars on a minor road cross a big highway with conditional (orange flashing) traffic lights. Elsewhere in aviation this is just never done, there is always vertical separation too as a most basic safety precaution - ie like an overpass. The 1000ft also has the advantage that helo traffic is clearly visible on radar which is not the case when its grubbing along at 200ft.

Equally, the London helilanes too carry both mil and civ traffic, but critically both are on the same frequency (or if not the system re-broadcasts everything so it sounds as if they are) so everyone is playing the same ball. As every mil helo (surely?) has VHF nowadays why the digamma aren't procedures requiring its use when interracting in close/very close proximity with civ traffic?

Contributory factors include grossly sloppy r/t which employs open questions instead of closed ones - "do you see the CRJ on finals" when there are two unidentifiable aircraft visible on finals instead of "do you see the aircraft on 2 mile finals".
Doubtless there may be other consideration such as insufficient controllers and excessive workload too but that is not for me to say.

Bottom line is this appears to be a classic human factors accident induced by badly designed airspace, voice and control procedures.

+++++++++++

Why was the helo high? Not that I've ever done it but 200 ft or below at night over a big black hole of a river surrounded by bright city lights (800ft is my lowest) sounds pretty adventurous to me, it's very low indeed, and when a threator distraction is introduced at such low level in a helo one's instinct, even reflex is often to just squeeze back a little on the cyclic to give you a bit more space while your attention is drawn elsewhere. 100ft extra comes in a very short time and with less than 100ft of vertical separation from mis-identified traffic, that's it.

Quote from "meleagertoo"

"Why was the helo high? Not that I've ever done it but 200 ft or below at night over a big black hole of a river surrounded by bright city lights (800ft is my lowest) sounds pretty adventurous to me, it's very low indeed, and when a threator distraction is introduced at such low level in a helo one's instinct, even reflex is often to just squeeze back a little on the cyclic to give you a bit more space while your attention is drawn elsewhere. 100ft extra comes in a very short time and with less than 100ft of vertical separation from mis-identified traffic, that's it."

Can't help but wonder about the sudden supposed change in height. I can't imagine that the heli pilot didn't see the jet in the final moments......reaction is "avoid"....turn right? ....in front of it? No, Go down into the blackness below, No, Turn left towards it? No,

So only way is up, another 100ft and we'd not all be writing this.Tragic beyond words.

From what I have read, & presuming that I have interpreted this correctly; it would seem that helicopters can operate through the final approach area at approximately one & a half miles from touchdown provided they are 200’ or below - giving them 100’ approx. vertical separation from landing aircraft which would be at 300’, or so, in that area. If this is true, it represents, to my mind , a gross dereliction of duty on the part of whichever body approved this procedure. 100’ separation is absolutely nothing in practical terms - whether or not you are visual with the traffic. Aircraft which are intentionally flying in formation often have more separation than this ! Whoever sanctioned this procedure, if I have got this perception correct, effectively caused this collision; & should be prosecuted. This represents absolutely NO separation at all; whether or not the aircraft were separating themselves visually (or if at least one of them was doing this). If this is the case, I am amazed that this was allowed at a very busy IFR aerodrome.

It hasn't necessarily climbed 100 feet. sinc display resolution is only 100ft it could be that it climbed from 240 to 260ft between these two screens. Besides this it also shows how ludicrous this 100ft vertical separation in this case was. Even the ATC screens resolution do not really support this level of separation. 245ft would still have shown as 002 and if in the middle of the Potomac the 3\xb0 G/S would be already lower than this.

That’s an awfully cluttered display, chock-a-block with information with no salience whatsoever. For many years, I flew a lovely large piston twin, being passed down almost from one owner to the next, with the aircraft, until its last owner installed acres of Garmin glass. I could no longer perceive the propeller RPM with sufficient granularity; the fuel flows were obscured, the whole place became like Blackpool illuminations, and, as I was fundamentally only flying it for my own pleasure, I stepped back.

Urgent information needs salience in displays and suitable attention-getters, but in that regard, proximate traffic near an airport could be given greater prominence, then to be lost in learned noise. TCAS is not the answer to this collision. I’m increasingly reminded of the term, ‘defensive controlling’. Yes, you expect to have vertical separation if the climber stops at its cleared level, but why not give it a five degree heading change, not to achieve any kind of separation, but just to make sure they don’t hit if it busts….

The transfer of responsibility to the helo crew here was entirely legitimate, but also created the single point of failure which led to a collision, and that was foreseeable.

What should have been the vertical separation? I'm just a lowly PPL holder, but I imagine if the CRJ was at 325 feet, even a ceiling of 200 feet is too high for the helicopter.

Not just from a collision perspective, but a wake turbulance issue.

And maybe more importantly, what should have been the horizontal separation? Surely it should have been at least 500 feet after the passing CRJ (not based on air law, just common sense). Clearly there was no horizontal or vertical separation in the end, but just how far off minimums was the helicopter? Seems nearly impossible to be that far off the expected flight path.