Terrain/obstacle clearance under radar control

[lospilotos]

Hi!

As a pilot, I´ve always been taught that ATC is responsible for terrain/obstacle clearance only when an aircraft is under radar vectors (yes, I know that ultimately the final responsibility lies with the PIC and it is us getting killed, not the controller, but anyway...).

Then I came across this article on SKYbrary: http://www.skybrary.aero/index.php/Minimum_Vectoring_Altitude_(MVA)

In it, it says the following: "This includes responsibility for obstacle clearance, except when an IFR flight is being vectored or given direct routing asssited by radar."

I´ve been looking through various ICAO documents and have not been able to find any reference supporting that direct routings would be the responsibility of the controller.

So, if given a direct and a descend clearance that is below MOCA at our current position but at the direct point it is above MOCA, would the controller assume us not to desend below this until it is "safe" to do so? Of course, the controller with MVA altitudes displayed at his/her screen has a better knowledge of what is safe than us pilots that might be restricted by a high MOCA caused by an obstacle that might not be a factor at all.

Could any ATCCO please shed some light on this? Preferable with a reference to relevant ICAO text.

And, yes again, if I was at all unsure of the safety of the clearance, I would double check with ATC, but just curious.

Thanks!

[tori chelli]

Los
I'm a UK approach controller, so I can't help with Airways en-route, but where radar is available, an ATC Surveillance Minimum Altitude Area Chart (ATCSMAC) is published which shows the pilot where he can be expect to be vectored and at which altitude. These levels are absolute minimums and anything lower must not be allocated. The chart is scaled and easier to use nowadays with flat screen, moving map technology.

We don't have MOCA's on our screen, but we are expected to know the ATCSMAC and mentally superimpose it on our screens (some lucky people have a map overlay they can select if needed, but it's not routinely displayed).

The minimum altitude is based on a survey of the obstacles in the area combined with a more precise knowledge of the aircraft's position because of surveillance equipment, rather than in a non-surveillance environment, so the minimum levels will almost inevitably be lower than the general MOSA for a 25 n.m radius of the airfield, or the MOSA either side of an airway centreline.

All ATCO's should be aware of the risk of terrain, and not allocate levels until they are safe...this includes levels which are unsafe in your present location, but will be safe at your next waypoint---you just DON'T do it!!

Can't point you to the ICAO doc, but the ATCSMAC was re-drawn to comply with ICAO standards about 3 years ago, so there must be something out there somewhere!

Hope this helps

Tori

[bookworm]

PANS ATM (Doc 4444) 8.6.5.2 (also reflected in 4.10.3 Note 3).

When vectoring an IFR flight and when giving an IFR flight a direct routing which takes the aircraft off an ATS route, the controller shall issue clearances such that the prescribed obstacle clearance will exist at all times until the aircraft reaches a point where the pilot will resume own navigation.

[FlightPathOBN]

You cannot paraphrase a section, the sections are meant to be read with entirety of the document....this is a common trap that people fall into.

There are sections that over-ride sections, many if..then, and of course, amendments and clarifications.

Pilot responsibilities generally supersede all sections, and remember,
"acceptance of ATC instructions is an acknowledgement that the pilot will insure safe takeoff and landings, and the pilot accepts this responsibility..."

Note:
According to 8168 PANS-OPS...

"The objectives of the air traffic control service as prescribed in ICAO Annex 11 do not include prevention of collision with terrain. The procedures prescribed in Doc 4444, PANS-ATM do not relieve pilots of their responsibility to ensure that any clearances issued by air traffic control units are safe in this respect."

[bookworm]

You cannot paraphrase a section, the sections are meant to be read with entirety of the document....this is a common trap that people fall into.

Neither I nor Skybrary are paraphrasing the section, we're quoting it. It's not particularly useful to know that the pilot is ultimately the one responsible for not hitting something.

But it is useful to know, as a pilot, that if ATC issues a direct routing, PANS-ATM requires the controller to have verified that the level assigned is terrain safe, in the same way that she would if she had issued a vector.

[FlightPathOBN]

Simply quoting a section may be taking it out of context, nor does a quote allude to any other documents which may have superseded or clarified that section.

It is useful for a pilot to know that they are ultimately responsible, and as the documents note, the AT controller has no idea what the prox warning is set to for various aircraft.

Technically, the documents differentiate between terrain and obstacles....

this is also a direct quote...
"The objectives of the air traffic control service as prescribed in ICAO Annex 11 do not include prevention of collision with terrain. The procedures prescribed in Doc 4444, PANS-ATM do not relieve pilots of their responsibility to ensure that any clearances issued by air traffic control units are safe in this respect."


Bottom Line: ATC was set up to manage air traffic and prevent aircraft to aircraft collisions...NOT provide terrain clearance for the aircraft.

[bookworm]

Bottom Line: ATC was set up to manage air traffic and prevent aircraft to aircraft collisions...NOT provide terrain clearance for the aircraft.

But it helps if ATC doesn't cause collisions with terrain in preventing those aircraft to aircraft collisions, which is the point here.

You make it sound as if the pilot is not ultimately responsible for avoiding aircraft to aircraft collisions too. She is.

[Spitoon]

FlightPathOBN makes an important point that all of the rules (from ICAO or wherever) - when taken together - describe how the aviation system works. One must be wary when taking just one sentence or paragraph not to consider how it relates to other parts of the ruleset. However, we can't read all the rules every time we want to find the answer to a question - that's why the rules are written within a relatively simple structure. And we have to use our professional knowledge to recognise when it is necessary to refer to some other rule to get the full answer to our question rather than blindly repeat extracts of text from a book.

And yes, the pilot is always going to be primarily responsible for not letting the aeroplane hit something - but then we need to think about how the rest of the system allows him/her to conduct a flight without anything remiss happening.

bookworm has helpfully told us what PANS-ATM says about the topic -
When vectoring an IFR flight and when giving an IFR flight a direct routing which takes the aircraft off an ATS route, the controller shall issue clearances such that the prescribed obstacle clearance will exist at all times until the aircraft reaches a point where the pilot will resume own navigation.

But nothing in life is simple. Each country has to take the ICAO words and put them into their national rules. Some transpose the words verbatim, some may consider that there is some ambiguity and re-write the rule slightly to make it clearer, and then it often must be translated to the local language which brings its own problems.....

I don't have all of the reference books to hand but it looks like skybrary has re-written the ICAO text (or maybe used one State's interpretation of it) for its article. But it still seems a bit ambiguous because I'm not sure what radar assistance is.

As a rule of thumb I have always worked on the basis that when providing a radar service (even if the aircraft is on its own navigation) I will allocate terrain safe levels. When offering a procedural control service it's the pilot's responsibility to assure terrain clearance. In my experience as an approach controller the practical upshot of this is that when using radar I don't issue a clearance that takes the aircraft below the minimum published level on the charts (whatever they are called these days), and when doing it procedurally I have to allocate a level that is safe at the approach fix (for example) but how the pilot gets there is his or her responsibility. In truth, wherever I have done procedural approach there has been high ground around nearby and I have always given descent to terrain safe levels based on DME ranges 'just in case'.

[FlightPathOBN]

Spitoon, very well stated...

bookworm, actually I mean the exact opposite, that the pilot is always responsible.
In the design of RNP procedures, I must generate my own terrain model and obstacles, as the procedures are virtually never along an established corridor, and extend much further than the 25nm MSA circle, so I am more sensitive to terrain and obstacles, how they have been or have not been generated, the adherence of the State to ICAO requirements, and especially the obstacle gathering mechanisms. I know that there is little pro-active activity by the country for obstacles, and obstacle databases are non-existent in most countries, so for one to absolutely rely on ATC to have the correct information on MOC is a stretch..

I would add that there are very, very few aerodromes that have the ICAO certified obstacle clearance zones surveyed (as the standard is a moving target) and that the FAA part 77 surveys are not the same as the ICAO. So, if the overarching premise of the ICAO requirement for ATC to provide obstacle clear vectoring, is that the aerodrome has the certified ICAO zone survey, then the argument falls apart from the beginning.

As an example, I would point to the NOTAM's that are issued. I always wonder when I pilot sees a NOTAM that states a mobile crane, 200 feet tall, located 849 m, bearing 28 degrees from ARP...what does that really mean to the pilot?

That is why I will always try to elaborate on responsibilities and the pilot always is responsible, and leave nothing for granted.

[bookworm]

In the design of RNP procedures, I must generate my own terrain model and obstacles,

But we're not talking RNP here, we're considering a direct clearance using conventional aids or RNAV, under radar surveillance.

Perhaps, like Skybrary, I'm taking a Euro-centric view of the world when considering what ATC is or isn't likely to do. But the simple reality is that when London, or Langen, or Paris issues me a "route direct to SUMWE" instruction, then unless I have grounds for being suspicious about the instruction, I'm likely to accept it on the basis that ATC is responsible for terrain clearance associated with that instruction. In twenty years, I've never heard anyone given a heading to fly respond "standby a minute I just need to check the obstacle clearance on that heading against my charts...".

But I'm not for a moment suggesting that pilots should drop their vigilance in verifying that all clearances can be safely flown; nor, if you read the first sentence of his question, is lospilotos, nor, looking at the paragraph in "Pilot's responsibility", is Skybrary. But the role of the pilot in the circumstances described is one of verification.

As an example, I would point to the NOTAM's that are issued. I always wonder when I pilot sees a NOTAM that states a mobile crane, 200 feet tall, located 849 m, bearing 28 degrees from ARP...what does that really mean to the pilot?

Which is exactly why, ATC gives a direct clearance in the vicinity of that aerodrome, it should be one that does not require the pilot to make the primary decision as to whether or not the clearance is terrain-safe.

It's laudable to remind pilots of their ultimate responsibility, and I can imagine that you don't want a pilot reading this thread to think "I don't have to even think about that because ATC is taking care of it". But nor do I want an ATCO reading the thread to think "I don't have to be sure of terrain clearance when issuing a direct routing because the pilot is 'always responsible'".

[WindFarmer]

The UK procedure for designing the ATC Surveillance Minimum Altitude Charts is called CAP 777.

You can download it at
http://www.caa.co.uk/docs/33/CAP777.pdf

[FlightPathOBN]

Here is the new RTCC in AUS..

http://operationsbasednavigation.com/wordpress/wp-content/uploads/2011/04/RTCC.jpg

[LapSap]

Streuth! Where's that? Canberra?

[FlightPathOBN]

Actually, they all look like this...