What can I say! It was really a very interesting event and in this blog post I will provide some of my thoughts on it. If you did not attend you probably missed an event that will bring a much necessary revamp to the obstacle limitation surfaces (OLS) as we know them today and some of the remarks I make could be taken out of context.

DISCLAIMER: The following is my interpretation of the event, the complete picture is still now known and others that participated might have a different opinion, read with a grain of salt.

For those of you who are more of the TL;DR crowd the next lines might be all you need to know: Current OLS probably have no correlation to the real operational world for the last decades and something else needs to be put in place through the incorporation of surfaces that can be tweaked based on the actual operations.

Now let’s dive in on the Symposium, from the 8-10 of December ICAO organized the OLS Symposium event, one critic I have to make about the event is that it was not free for industry or academia to attend, price points of $250 and $100 although may seem small are not really a smart investment when you consider the event was more about presenting what ICAO OLS Task Force had come out until now. Think about it like paying some money to be presented with an unfinished product. For me that was not cool to start of and even if the event in the end did present a lot of useful information the harsh reality is that the OLS symposium was about presenting criteria which is yet unfinished and vetted to see the light of day. During the different three days a lot of questions were brought up by participants and rightfully on many different topics which were presented, I would advice ICAO should really consider not charging for these types of events. If this was a workshop with a certificate at the end then it would have made much more sense.

Of all the three days I would have to say the third one was the most useful one although day 2 was the one that presented the criteria and day 1 could have been left out altogether as it was mainly an introductory one but if you cut it out day 2 would have presented the same information and not missing anything from day 1.


Day 1 – OLSTF presentation and background for the OLS changes

Key phrase: Today works but need to be enhanced, unclear what the surfaces are trying to achieve (yes they seem to clash)

Like I mentioned before this day could have been skipped altogether, it was more about explaining the OLS task force mandate and how they have been working with the Aerodrome Design and Operations Panel (ADOP) and the Instrument Flight Procedure Panel (IFPP). During this day they mentioned the introduction of two new types of surfaces that will replace the current provisions:

OFS (Obstacle Free Surfaces): Surfaces that can´t be penetrated by any object -> hard surfaces intended to protect the airport environment

OES (Obstacle Evaluation Surfaces): Surfaces which can be penetrated but trigger an aeronautical study in order to allow the penetration or not -> soft surfaces intended to protect the operational procedures

First mention of the effective and applicability date (2024/2026) was mentioned, I still personally believe it is unrealistic as the criteria haven’t event been published through a State Letter, software will need to be adapted or created, training, etc. I think for States having one or two airports this could be manageable but for many this will become a huge implementation task due to resources and budget constraints.

I knew the current Obstacle Limitation Surfaces (OLS) were old: introduced 1950, last real update 1970/1980, this means at least 20 years past due date for a review which started in 2015! This means that six years after in 2021 we have a public draft in the form of the symposium? I must admit I am not really aware of this except some old slides you can find online about the initial proposal.

An additional concept about Aeroplane Design Group (ADG) was introduced which tries to make the correlation between speed of the aircraft and the areas to be protected, which is good as there is some disconnection right now wiht the aerodrome reference code (ARC) used. What I didn´t like was the fact it doesn´t match the PANS OPS speeds 1:1 and this was answered during the symposium that they did not want to have several categories? Basically it seemed that only A,B,C,D,E categories are not enough from PANS OPS speeds. I think since a new change was introduced and old airports will anyway be grandfathered their obstacles we could have started with a completely new slate instead of trying to cater for the old and try to match everything as much as possible. Some table top exercises of possible reclassifications on airports could make the comparison easier to visualize.

Day 2 – New Obstacle Limitation Surfaces concept introduced : Obstacle Free Surfaces and Obstacle Evaluation Surfaces definitions for the different areas

Key phrase: Current obstacle limitation surfaces are an artificial construct

During this day finally the OFS and OES dimensions were presented in a more detailed way, for the most part the new concept is a lot less restrictive than previous one in terms of slopes but some of the areas increase in terms of the area specially near the runway (approach and takeoff). Once again the obstacle evaluation surfaces (OES) were mentioned than any penetration would trigger a PANS OPS check

The obstacle free surfaces (OFS) that are replacing the current obstacle limitation surfaces (OLS) are to be made of the take-off surface, transitional surface and the approach surface (and to think someone once told me the take-off surfaces are not required!).

To establish these surfaces it seems around 100,000+ operations were analyzed provided by the FAA of which 60K+ were approach and 50K+ were takeoff, that number seems a lot but considering the millions of flights a year this number could have been a lot more and from samples from all around the world, computers in 2021 are more than capable of doing these type of analysis quite quickly with big data.

There are some tries to make some consistency between VSS and the Approach surface although from my calculations there is still a bit of a mismatch due to the way the VSS is actually calculated and the approach surface using a 3.33% slope, the transitional surface is to be used with 20% and rise up to 60m of height and the other key thing is that current Annex 14 OLS are not enough for take-off, which was a given considering how the surface is rather narrow in comparison to PANS OPS areas to be assessed.

A question I asked was about the Annex 4 take-off flight path area (TOFPA) and its 1.2% slope and the answer was that it will remain as it is because it is relevant for engine out procedure (OEI), I personally think this criteria needs to be moved out of the Annex 4 into the Annex 14 chapter dealing with obstacles and if engine out is important maybe have the slope and horizontal projection match someway the take-off areas. Following a bit PANS OPS it could be called Obstacle Identification Surface (OIS), so nothing that will make an aeronautical study but which needs to be notified as part of an obstacle dataset and/or obstacle charts.

One more thing is that the obstacle free zone (OFZ) currently just for ILS apparently will be now for all aerodromes, which ultimately makes sense, further information is required on this as not so much was presented.

The new Obstacle Evaluation Surfaces (OES) are basically replacing the current inner horizontal and conical surface plus the not so much used outer horizontal surface, basically any obstacle here may impact operations so it needs to be evaluated and an aeronautical study is triggered; the aeronautical study being PANS OPS based mostly.

One thing that was mentioned during the three days is that OES can be adapted/modified/used as per operations, that is if no circling exists then you may leave out the OES protecting circling, you can alter the height of them based on the OCH in place, etc. Would need to see the final draft but this can really open a can of worms, now the OLS will need to be done together or by a PANS OPS expert (Instrument Flight Procedure Design) and people around the world need to be careful not to have such lenient new surfaces that could impair new operations. It is critical that the full master plan of the airport is to be considered and not current operations which is the first mistake I see airports make when designing their airport safeguarding plans. The issue with the new as you find fit or custom OFS/OES is that it may lead to very different interpretations on how to implement, this needs to be taken a bit more seriously, especially when many States already outsource their instrument flight procedure designs (IFPD) which means they do not have the tools and resources and will also need to outsource the new OFS/OES creation and evaluation. I suppose this is good news for industry.

A key aspect is that OFS will not allow any penetration hence the obstacle free in the name, so you can only limit the operations, displace the THR, raise the glide slope (GS)/descent angle and PAPI angle for the approach, as the OFS will match kind of the VSS penetrations of the VSS how will they be dealt? I asked and was assured current airports will be grandfathered in which basically means accept what is currently in place, but you can start to imagine that new airports will say why that airport has VSS penetrations allowed which will be equivalent to OFS penetrations and we can not?

Over the years I have learned that theoretical ideas need to be really considered against real world scenarios, I believe this will be one of those ideas which is nice to have but not implementable and probably further refinement will come of it. Even in PANS OPS the VSS has two different areas with one closer to the centerline being considered the not penetrable one, at least this should make it into the Annex 14.

OES penetrations are a lot more flexible, really very flexible. These penetrations can be mitigated by adjustment of flight procedures, charting (not clear if they mean putting obstacles on charts), promulgation of safety information, revision of traffic, revision of VFR routes and Marking/Lights. OES are not mandatory surfaces you can have them if you use them, you can dispose of them if you don’t, you can alter the standard dimensions. I think this will require real expertise into how and why something can be modified, this could lead to some “expert” opinion to leave out some areas that are penetrated because we think aircraft will not fly there, decision not based on facts but on what people believe.

Day 3 – Aeronautical Studies as an effective tool for matching operational needs of different users. Airspace is not just for aviation

Key phrase: No matter how perfect an OLS is, penetrations will exist or will be demanded

This day was really for me the star of the show even though it really had almost zero to do with the new concept introduced but more about the aeronautical studies part which are already done around the world but without enough ICAO guidance. Great case studies were presented from Spain, Brazil and the USA. Switzerland presented the data collection side but Switzerland is probably not the best case because they have one of the best data collected countries in the world and monetary/human resources probably not so scarce.

All of the case studies highlighted that an aeronautical study was more about determining if a penetration was a hazard to operations or not and they really showed how penetrations of the OLS were to be checked against the operational areas aka PANS OPS, another thing to take into consideration is that not only penetrations may be a hazard (being too high) but that also there may be some things below the imaginary areas which may trigger an aeronautical study like a dumpster which may attract wildlife and birds, etc. There was mention on the possible effects on communication, navigation and surveillance (CNS) and even ATC line of sight.

Personally I found the Spain example to be the most complete one as they start with the obstacle limitation surfaces (OLS), on top of that they add the radioelectric surfaces to be reviewed of which Spain has their own law but Europe also uses the EUROPEAN GUIDANCE MATERIAL ON MANAGING BUILDING RESTRICTED AREAS (which apparently will not make it into the new concept) and finally they use the PANS OPS surfaces to at the end achieve what they call the “Airport Safeguarding Areas” roughly translated. On top of all of that, Spain actually provides the official OLS areas for anyone to use which means no need to recreate from scratch for an aeronautical study nor having differences with the State approved one. Here is an idea, OLS (OFS and OES in the new terms) shall be made freely available for download. A geospatial format would be fine, KMZ, Esri Shapefile, DXF. Please no complicated exchange format that no CAD/GIS can use out of the box.

The Spanish concept is what I thought most countries around the world would be doing anyway but it seems that is not the case or at least is not mandatory, the new obstacle free surfaces (OFS) and obstacle evaluation surfaces (OES) seem to be trying to match these requirements.

Brazil also had a clear presentations on what an aeronautical study was to be carried out and the steps they made for them, FAA presentation showed in my opinion mostly a self-help desk in which proponents of a structure input some data which triggers some actions by FAA to analyze the information, so it is a nice workflow/ticketing system which at the end delivers a response on what is acceptable or not based on what the operational people decide after evaluation of the data.

Basically as a summary an aeronautical study is to be followed by the next basic steps

  1. What is the affected surface?
  2. What is the purpose of the surface?
  3. What is the impact on the different stakeholders?
  4. Mitigation measures to be put in place

Personal View – Terrain and Obstacle data

This continues to be something not really understood, why collect areas that are not a match with current OLS 100% and now will even match less with the new OFS+OES, I think ICAO over engineered eTOD initially or TOD as it seems everybody is calling it now by having different collection requirements and having some sort of expectations on what the data will be used for. I think for most ANSP the only use of terrain and obstacle data is for instrument flight procedure design, Area 1 requirements are fine and can be obtained from SRTM, ASTER and other means without being so much a financial burden once vetted by the local authorities as fit for purpose but for the airport environment the precision required should be one that can be easily obtained through traditional means like a survey or photogrammetry and using a single horizontal and vertical accuracy, that would have made things a lot easier.

Going back to the OFS+OES, TOD should be taken into account to match the areas, I hope the proposal doesn’t go out without alignment and that if OES are not to be considered due to not being relevant operational that should apply for TOD also. Basically the TOD collection area should be your OFS+OES with a single horizontal and vertical resolution within 5/10 NM? that can be achieved without LIDAR or expensive means which is an overkill for most applications, Area 1 can be used for anything else.

Conclusion – OFS and OES are still early, we still have questions and we will need to wait for the draft

I would think the most important part of the event was more about providing to the general public a first look in a long time about the changes to be introduced with the new concept of obstacle free surfaces (OFS) and obstacle evaluation surfaces (OES), they did mention the overarching name would still be Obstacle Limitation Surfaces (OLS) but I really hope this is not the case and ICAO could learn more from the GRF implementation which continued to use SNOWTAM even when in some regions of the world no snow exists further complicating the implementation. A new concept a new name and be over it.

Another thing that ICAO could learn from the GRF implementation is that the time you think it requires to commit something is not so easy if we are overly optimistic, COVID 19 aside… the implementation date was anyway too optimistic and the extra year delay only provided a small breath of air. In many countries of the world they are still struggling with understanding GRF/SNOWTAM and implementing software to be able to transmit the new format. No matter how “low impact” you think a change will be on processes and systems the reality on the ground is that change, especially legislative one takes a lot more time and software implementation can only occur when system providers are sure things will not change. For me 2026/2028 looks like a more sensible effective and applicable date and that is if we can get the official final word from ICAO before 2023 on the final draft without modifications.

Overall a good event that could have been 1 day shorter and free for everyone, that still raised too many questions on the effective implementations and that now we need to wait for the State letter to go out and see what ends up in the final draft. I am confident that with the more than 200 questions that were asked during the period the members of the OLSTF will review and refine what the guidance needs to be

If you need help with PANS OPS or Obstacle Limitation Surfaces go check out FLYGHT7 website

Update 15 DEC 2021: Videos are now available, check this blog post for more details

1 Comment

ICAO/ACI Obstacle Limitation Surfaces Symposium (OLSS 2021) Videos now on ICAO TV – Antonio Locandro · December 15, 2021 at 8:12 am

[…] you enter the ICAO TV portal, after you watch the videos you can go read our review at the previous blog post and see if you agree/disagree or have other […]

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