RVSM Flawed - Prof Ladkin's paper

[Belgique]

Professor Dr Peter Ladkin has published a paper on RVSM flaws at this URL (http://www.rvs.uni-bielefeld.de/publications/Reports/SCflawed.html).

It is entitled:
"The Pre-Implementation Safety Case for RVSM in European Airspace is Flawed"

The entry page was here (http://www.rvs.uni-bielefeld.de/)

Further significant article on European and North American RVSM is to be found here (http://www.iasa.com.au/folders/Safety_Issues/RiskManagement/introRVSM.html)

Comments invited.

[Kalium Chloride]

So in a nutshell...

Eurocontrol assumed that, if it could prove RVSM was safe even without ACAS, it would not need to prove that it was safe with ACAS...because use of ACAS automatically makes the skies even safer.

But (says the good professor) the use of ACAS contributed directly to the German collision.

Therefore the Eurocontrol assumption that ACAS makes the sky safer is incorrect. Therefore the "non-ACAS" RVSM safety case cannot automatically be applied to the "with-ACAS" RVSM situation.

I think you have to examine whether Prof Ladkin's assumption over ACAS and the German mid-air actually stands up to scrutiny. He claims that if the DHL 757 hadn't followed ACAS procedures the collision wouldn't have happened.

While this is true in its absolute sense, I think it's unreasonable to disregard the inappropriate ACAS response of the Tu-154 -- you can't construct a logical argument on safety if the foundation of the argument fails to build on existing rules (in this case the procedures following an ACAS advisory). Else you could assume that pilots won't follow ANY safety procedures correctly -- in which case, your safety case is shot to sh*t before you even begin.

Just as a side note: since both aircraft were initially at the same altitude (FL360) the vertical separation between flight levels was irrelevant. The collision would have occurred whether the VSM was 1000ft or 1000 miles.

[Thunderbug]

Prof Ladkin will next try to prove that black is white and gets himself killed at the next zebra crossing.

[Apologies to Douglas Adams}

:D

[Feather #3]

Given that KC's quote/assumption above is correct, the good Professor has obviously never had his life saved by ACAS!

To paraphrase the Goodyear advert "If it only happens once, it's a good year!"

Is this another of the mathematician's figuring that you have to account for pilot error in the scatter of mid-air probabilites, whereas, out there in the REAL world, I see GPS equipped a/c coming DIRECTLY over/above every day I go to work? What if we added 'one mile right' to the above equasion??

Don't mean to hijack the thread. ;)

G'day :rolleyes:

[Wiley]

(I hadn’t seen Feather#3’s post when I wrote this.)

What no one seems to have touched on (or at least not in anything I’ve read to date) is the one huge difference between the use of RVSM in NATS (Transatlantic) airspace and European airspace: in NATS airspace, everyone is going in the same direction (with a few – a very few – in the opposite direction), so there’s little crossing traffic and almost no opposite direction traffic. In Europe, you have mucho-multiple tracks from all over the compass rose repeatedly crossing others.

Also, in the first case, there’s one ATC agency that issues the airways clearances to all traffic, (OK, I’m simplifying the situation slightly), AND all that traffic is on parallel tracks, whilst in the second case, you have a total mishmash of both different national ATC agencies issuing clearances and co-ordinating with each other - and to confuse the issue even more, (very) frequent crossing points for many if not most airway tracks. In this situation, given the volumes of traffic, RVSM or no RVSM, my hat goes off to the European ATCOs for the indisputable fact that they get it wrong as seldom as they do.

Spare a moment to consider that RVSM is being introduced in much of southern Asia in November. At least the traffic levels aren’t nearly as high as in Europe, and the vast majority of traffic is more opposite direction rather than crossing as in Europe.

I just wish someone in authority would bite the proverbial bullet before RVSM is introduced in south Asia and tell us all to fly offset enroute so that most errors – (when, not if they are made – the recent accident in Europe has just proven that) – would be ho-hum Traffic Alerts requiring no pilot intervention rather than Resolution Alerts requiring both pilots to act instantly AND correctly, something the recent tragic accident in Europe has also shown us cannot be relied upon to occur.

I know that such a suggestion would not have anywhere near the same impact in Europe and can even accept that it might complicate matters for European ATCOs with the many crossing tracks they have to deal with, but it would offer an improvement in safety in an environment where most traffic is opposite direction as it is in Asia.
]
As 410, (the one who’s pushed this barrow the hardest on Pprune), has said here many times in the past, couldn’t we ‘bolt the stable door’ just once before ‘the horse bolts’ rather than wait for another couple of hundred people to die to prove that there’s a problem? RVSM’s going to reduce reaction times in any such error scenario by half. Why not stretch it hugely with this incredibly easy and no cost solution?

[Bus14]

Peter Ladkin is a very clever man, and has a good level of understanding of aviation in addition to mathematics.

It seems to me that, although he cites the Bodensee accident, he is simply arguing about the validity of the Eurocontrol assumptions. He does not seem to be saying that RVSM with ACAS is unsafe, but rather that Eurocontrol have not proved that it is safe.

For us mere mortals it is much better to concentrate on our contribution to flight safety than to get involved in semantic disputes over the wording of a safety case. The whole subject of Human Hazard Analysis is, in any case, being reviewed by the JAR authorities anyway.

The prime thing for we pilots to understand is that TCAS is an aid to the 'see and avoid' principle of collision avoidance. This means that it in no way negates our responsibility to listen out, look out, and keep a mental plot of other known traffic. A sharp crew may well spot a possible conflict when it is 'other' traffic, their suspicion will be further aroused when the traffic becomes 'proximate', and, before it becomes a TA, they may well be questioning ATC.Thus an RA is avoided before it occurs. It is also worth pointing out that, in the event of an RA in IMC (ie we can't visually acquire and avoid the other traffic) our responsibilty is to react to the minimum necassary to avoid the conflict. TCAS RAs give you a V/S differential of 1500'/min on your original V/S. More is not better, as that is what will induce the three way conflicts that TCAS is not good at solving.

You can try the above in the sim. Set up a head on co-altitude RA. If you follow the RA by staying just in the green, and returning to your cleared altitude as soon as the TCAS display permits, the altitude loss or gain is only a couple of hundred feet. If you treat it like a GPWS or windshear pull-up (which of themselves are also two subtly differant beasts) you will climb straight into all the other traffic.

The ATC authorities only accepted TCAS on the promise that a correctly followed RA (on a non manoeuvering target) would not compromise the normal ATC altitude tolerance. If an RA occurs, the pooch is already screwed, to unscrew it requires correct, timely, but not over-reaction from both crews.


Offsetting the track is somewhat akin to a security blanket, it will only help in the extremely rare head on co-altitude case. It will not definitevely avoid the triggering of an RA either, due to the poor lateral resolution of the TCAS system. It would not have helped the Bodensee crews, who were on crossing tracks.

To end, I can do no better than to pass on the advice of some of the best brains in the Situational Awareness and Human Error business which was offered at a conference in 2001.

Prof Jim Reason - You are only there to get it right when the 10 to the power of minus 9 event occurs.

Dr Mica Endsleigh - Use Situational Awareness to be pro-active

Tom Seamster - Expert performance requires effortful practise

[Old Phart]

You must not overlook the fact that below FL290, the standard separation was 1,000 ft. even prior to introducing RVSM. Barometric Altimeters and older types of Air Data Computers are/were less accurate at higher altitudes. FL290 was selected as a suitable change-over point to increase vertical separation to 2,000 ft. to allow for this reduced accuracy. With the use of digital technology and better materials technology in pressure sensing devices, altimetry equipment became sufficiently accurate to allow 1,000 ft. separation to be applied above FL290 - provided particular aircraft and equipment combinations were proved and certified to have necessary system accuracy.

Eurocontrol published an excellent bulletin on the use of Collision Avoidance Systems and this is now being circulated around the airlines. If you haven't seen a copy, you can get it here (http://www.eurocontrol.be/acas/webdocs/ACAS_leaflet_v4_Final.pdf). The document illustrates the issue much better than criticism of implementing both ACAS and TCAS in the same airspace.

In short, the key to successful collision avoidance isn't a function of altitude separation. Its a matter of Follow the RA to maintain safe separation and avoid collisions.

[Slasher]

I agree with Old Phart re sep standard of 1000 ft below FL290 which has been around forever. Why the special procedures above that level? 90 deg turns for emerg descent outside communication, +/- 500 ft cruise level changes for wx diversions again when outside comm, etc etc?

Im waiting for the next collision this time based purely on RVSM procedure confusion. Someone somewhere has the unluckey ticket!