Loss of Separation or Near Miss

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Bowie
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Loss of Separation or Near Miss

Unread post by Bowie » Sun Oct 26, 2008 11:04 pm

Where can I get a legal definition for a Loss of Separation and a Near Miss, and how does ATNS differention between the two. Are there height and horizontal minimums that apply maybe ?
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Re: Loss of Separation or Near Miss

Unread post by Thndr_strck » Mon Oct 27, 2008 10:40 am

A "near miss" is a collision ie - they nearly missed.

Loss of speration (LOS) is when aircraft under radar control are less than 5nm (10nm if secondar surveilance only) and/or less than 1000ft vertical (unless non RVSM above FL290).

Or, if procedural seperation is being used, the minimum required seperation is lost (there are too many procedural seperations to list here).

This is just a basic explanation.
When in doubt...DON'T !!
BlueSkye
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Re: Loss of Separation or Near Miss

Unread post by BlueSkye » Mon Oct 27, 2008 2:55 pm

I could be mistaken, but a while back a loss of separation (reduction of separation) was when a reduction happened and the corrective measures where ATC initiated. A near miss (near collision) would be when a reduction occured and the corrective measures where pilot initiated.

The INCREP (incident report) form had three categories from which to choose: 1.Procedural; 2.Near Collision; 3.Can't remember. Procedural would be used for the first instance above and Near Collision for the second.

Current ATNSers please correct me on this.
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Re: Loss of Separation or Near Miss

Unread post by ATC Guru » Tue Oct 28, 2008 4:25 pm

Bowie wrote:Where can I get a legal definition for a Loss of Separation and a Near Miss, and how does ATNS differention between the two. Are there height and horizontal minimums that apply maybe ?
Just out of interest - why?
Bowie
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Re: Loss of Separation or Near Miss

Unread post by Bowie » Tue Oct 28, 2008 10:04 pm

Why ?

Because I cannot find a Legal Definition of the two and ATNS appears to be playing a words game with a very serious problem in SA Airspace at present. We are operating in a technical environment where all appears to be defined quite accurately or limits laid down in DIGMA etc.
But when people appear to be very nearly killed as a result of ATC Nearmisses it suddenly becomes a Loss of Seperation issue ? I am trying to understand how they get to such an answer to the issue. A miss is as good as a mile doesn,t make sense to me ?
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Re: Loss of Separation or Near Miss

Unread post by ATC Guru » Wed Oct 29, 2008 1:14 am

EDIT:

I withdraw from this discussion.

'Appear' isn't good enough for me.

I am 100% for safety - you can see the sectors I work. I don't do slanging matches.

EDIT 2:

Phone the CAA for the ATS inspectors if you have facts and basis for your allegations of these ATC 'nearmisses'.
3015
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Re: Loss of Separation or Near Miss

Unread post by 3015 » Wed Oct 29, 2008 3:41 pm

A LOS (loss of separation) is when the required separation for the type of airspace has not been maintained. Ie. in a procedural environment you can have a LOS between aircraft with a lateral distance of more than 10nm depending on the separation that was supposed to be used. In a radar environment normally less than 5nm and 1000ft.

A near miss is a LOS that reduced to such a margin that the two aircraft that were supposed to be separated passed in close proximity and a collision was narrowly averted. Be it by the grace of God or the actions of the pilots or the ATC.

Remember that if you are operating VFR there is not really a clear definition as to the separation required between 2 VFR's as the only requirement in class c airspace is to pass traffic info and traffic avoidance advice on request.

Hope it clarifies the matter for you.
Bowie
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Re: Loss of Separation or Near Miss

Unread post by Bowie » Wed Oct 29, 2008 7:34 pm

To 3015

Your explanation helps. What I am trying to find out is where is the Legal Definition of the "Margins" as you refer to them that differentiates between the two ? At present we are referring to one man's Near Miss which is the other Man's Loss of Seperation.

I fully accept the VFR situation of See and be Seen and then there is a Legal Definition of
"Essential Traffic" for IFR and VFR Traffic Information for seperation purposes.

To ATC Guru

I don't know where you work or what your experience is and I never raised a slanging issue. I am looking for a Legal Definition regarding Height and Distance for example where one can make an informed decision.
3015
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Re: Loss of Separation or Near Miss

Unread post by 3015 » Wed Oct 29, 2008 9:22 pm

Bowie

Best definition I can find at this stage is the following from the USA:
"Any circumstance in flight where the degree of separation between two aircraft is considered by either pilot to have constituted a hazardous situation involving potential risk of collision."

and this one from the Canadians:
"NATO defines NEAR MISS as any circumstances in flight when the degree of separation between two aircraft might constitute a hazardous situation."

LOS is an ATC thing and Near miss is more a pilot thing. If you think that you've had a near miss then you probably had one. The ATC set of rules is slightly different as there are a few variables that must be take into account. So they may not agree that it warrants suspension of the ATC and a full investigation but it does not negate that you felt a little uncomfortable. If you gie an example it may be easier to explain.

ATC Separation standards which determines as LOS can be found on the SACAA website here:
http://www.caa.co.za/resource%20center/ ... manual.htm
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Re: Loss of Separation or Near Miss

Unread post by BlueSkye » Wed Oct 29, 2008 9:37 pm

Bowie, technically there is no such animal as a "near miss". It's just a colloquial term used to describe a reduction in separation that involved avoiding action of some sort, be it pilot or ATC initiated.

For example: 1. Parallel tracks with 0feet vertical and 4,8nm horisontal separation with no risk of collision = Reduction in separation. 2. Reciprocal tracks with 200ft vertical and 1nm horisontal separation after severe avoiding action and huge risk of collision = Reduction in separation.

Number 2 would be refered to as a "near miss", but officially it is nothing more than a reduction in separation. The INCREP form I refered to earlier is only a means of reporting and not an official explanation of the terms.

The margins are laid out in PANS-ATM Chapters Five and Eight. Ch. 5 deals with procedural separation and Ch. 8 with surveilance radar separation. ICAO is not interested in the severity of the reduction, only if it was or wasn't.
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Re: Loss of Separation or Near Miss

Unread post by Dougie » Tue Nov 11, 2008 10:50 am

There is no such thing as a “Near Miss” that is a fanciful slang term that has found its way into aviation probably through over zealous reporters trying to make a report sound exciting.

The official term that is used is defined by ICAO as an “AIRCRAFT PROXIMITY” and ICAO define this as “A situation in which, in the opinion of a pilot or air traffic services personnel, the distance between aircraft as well as their relative positions and speed have been such that the safety of the aircraft involved may have been compromised.

An aircraft proximity is classified as follows:

Risk of collision. The risk classification of an aircraft proximity in which serious risk of collision has existed.

Safety not assured. The risk classification of an aircraft proximity in which the safety of the aircraft may have been compromised.

No risk of collision. The risk classification of an aircraft proximity in which no risk of collision has existed.

Risk not determined. The risk classification of an aircraft proximity in which insufficient information was available to determine the risk involved, or inconclusive or conflicting evidence precluded such determination.”

The term is usually abbreviated as AIRPROX

A Loss of Separation may be different to an AIRPROX. Standard ATC separation is defined in South Africa in the ATS Standards and Procedures Manual Section 6.

Standard Separation may vary as this is dependant on the facilities used to ensure separation (i.e. surveillance radar, VOR, DME, NDB). Surveillance radar separation allows for less horizontal separation than using other Nav aids. When the standard separation has not been achieved this is considered a Loss of Separation (LoS) however depending on the minimum required separation at that time if there is a Los there may not necessarily be an AIRPROX. An example of this is that if a controller is basing separation on RNAV equipment on an aircraft the minimum separation required for aircraft en-trail is 80NM however if separation was to reduce to say 70NM that would be a LoS however an AIRPROX shall not occur as it is unlikely that the crew of each aircraft would even be aware of this and there is no risk of immediate collision.

Within ATNS a system is used to classify the severity of any LoS where the separation that was achieved is considered and the means in which separation was regained is assessed. Through this Severity Classification Index all LoS are assessed on an individual basis. If through this assessment it is determined that he aircraft’s safety was not assured and there was a high possibility of collision a LoS may be classified as an AIRPROX as well.

So generally speaking an AIRPROX is when two or more aircraft were in close proximity with one another and there was a serious risk to the safety of those aircraft however a LoS is when Standard Separation as applicable has been infringed and the aircraft are not separated by this required minima.

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Re: Loss of Separation or Near Miss

Unread post by Aspiring Mango » Tue Jan 06, 2009 10:33 pm

Loss of separation is just that - check ICAO ATM manual for the separation standards - anything less than those are reductions. As Allen says there can be various classes within each reduction

As you can see the separations are sometimes "miles and miles"apart so you can have a reduction over oceanic airspace that is a reduction but far less serious than one closer to an airport operating dependant parallel approaches
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Re: Loss of Separation or Near Miss

Unread post by Dougie » Tue Apr 14, 2009 9:09 am

Skybrary list a defintion and descriptions of the various types of LoS at this link:

http://www.skybrary.aero/index.php/Loss_of_Separation

With the article quoted below:
Description
A defined loss of separation between airborne aircraft occurs whenever specified separation minima in controlled airspace are breached. Minimum separation standards for airspace are specified by ATS authorities, based on ICAO standards. Standard lateral and vertical separations in radar-controlled airspace are 5nm and 1000 feet respectively although with radar control in terminal airspace, regulations may permit a 3nm lateral separation minimum where radar cover is adequate.

A loss of separation between aircraft which are responsible for their own separation by visual lookout is not subject to definition.

The occurrence of a 'near miss', termed an AIRPROX by ICAO or, alternatively, sometimes called an NMAC, is in either case defined only by the opinion of one or more of the parties involved.


Types of Loss of Separation

Loss of separation may be either in a vertical or a horizontal plane, or both;
Loss of separation between aircraft may be a consequence of a Level Bust;
Loss of separation between aircraft may result in encounters with Wake Vortex Turbulence;
Loss of separation from restricted airspace is dealt with under Airspace Infringement;
Loss of separation from the ground is dealt with under CFIT.
(Loss of sepatation between aircraft on the ground is dealt with under Ground Operations)


RVSM

If the required equipment is carried as prescribed, then the risk of loss of separation in RVSM airspace is no greater (and no less) than in non-RVSM airspace.

Effects
Loss of separation from other aircraft may result in collision;
Injury, especially to unsecured cabin crew or passengers, may result from violent manoeuvres to avoid collision with other aircraft;
Injury to aircraft ocupants may also result from a wake vortex turbulence encounter.
Defences
Pilot situational awareness of the location and intent of other aircraft gained from listening to radio traffic, visual identification and monitoring and ACAS, especially when not in receipt of a ATS radar or procedural control or when operating outsided controlled airspace;
Standard Operating Procedures, both on the flight deck and in the ATSU, which detail procedures to be followed to reduce the risk of loss of separation;
Aircraft onboard equipment which warns of potential collision with other aircraft (ACAS) and allows an appropriate procedural response to risk. However, note that not all aircraft are required to be fitted with ACAS - only turbine-powered aircraft having an MTWA in excess of 5,700 kg, or a maximum approved passenger seating configuration of more than 19. (ICAO Annex 6 Part I Chapter 6 Para 6.18 and EU-OPS 1.668);
Ground-based equipment designed to warn of potential collision with other aircraft (STCA and in future, the use of MTCD).
Typical Scenarios
ATCO-induced situations: flight clearance does not provide adequate separation from other traffic:
Controller is aware but makes a misjudgement.
Controller is unaware.
A trainee Controller is being mentored and the mentor fails to intervene appropriately when the trainee allows a potentially hazardous situation to develop
Failure in sector or unit co-ordination
Pilot-induced situations: Flight in controlled airspace (CAS) deviates from cleared track or level without clearance due to flight crew:
Inattention to equipment malfunction;
Mis-setting of aircraft equipment;
Mis management of FMS inputs;
Failure to follow ATC clearance;
Avoiding a perceived (visual) loss of separation with another aircraft;
Avoiding Weather perceived as potentially hazardous when unable to make timely contact with ATC on a busy frequency;
Failure to properly follow a TCAS RA, including failure to terminate the deviation in a prompt manner when the RA ceases which may lead to a 'chain reaction' causing secondary TCAS RAs for aircraft in the same vicinity at adjacent levels;
Ineffective visual "look out" when operating VFR;
Not flying instructed or expected speeds or rates of climb and descent which have been the basis of a controllers flight sequence management;
Allows their aircraft to enter CAS without ATC clearance
Any of the above scenarios is exacerbated by high traffic density or a rapidly changing traffic situation and many can also lead to inadequate separation outside controlled airspace associated, for example, with military fast jet low flying. Entry to an ATZ outside CAS without clearance has also caused many losses of adequate separation.

Contributory Factors
Volume of traffic/Traffic density.
Weather (e.g. convective activity or clear air turbulence (CAT);
Aircraft performance (e.g. high or low rate of climb or descent)
Proximity of military operational or training areas.
Flight outside Controlled Airspace
Solutions
Encourage or mandate the use of high quality communication systems, Transponders (Mode C and Mode S) and ACAS;
Improve standard of pilot and ATCO training, especially in:
Air-ground communications safety;
Loss of separation awareness;
Crew resource management;
Provide more and improved ATC safety nets, e.g. STCA and MTCD.
Safety Nets must be set up so as to generate low levels of Nuisance alerts whilst providing useful warning time.
Please log into Skybrary http://www.skybrary.aero for the full article and related links, also this website is brilliant if you are doing research on any AViation related matter
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Re: Loss of Separation or Near Miss

Unread post by elbow » Sun May 17, 2009 2:00 pm

A question from a new PPL: what are the responsibilities of ATC in respect of VFR traffic? I understand that they provide separation for IFR from IFR and IFR from VFR, but not VFR from VFR. But in a control zone they will give VFR traffic routings to use. And VFR pilots need to obey or clearly say unable (and I guess why).

What happens if a VFR pilot obeys an instruction from an ATC but due to an error that instruction will put them in conflict with another VFR aircraft? What if that were to lead to an "airprox" between the two VFR flights, or worse, to a collision?

Regards,
Elbow
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Re: Loss of Separation or Near Miss

Unread post by ACE MAN » Sun May 17, 2009 2:16 pm

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