NAS rears its head again
Dick,
Reality check required again .....
N.B: Remember, we currently have a mandatory broadcast requirement for VFRs near Broome.
Reality check required again .....
- Transponder use is NOT permitted to be used as a risk mitigator in this scenario ! So that is removed from the equation.
- Therefore, in the proposed Class E airspace above Broome, there will be LESS protection from VFRs than is now the case ... FACT.
N.B: Remember, we currently have a mandatory broadcast requirement for VFRs near Broome.
Rubbish, ICAO has not stated that transponders cannot be used as a risk mitigator in safety studies in relation to airspace.
ICAO makes it clear that radio is not required for VFR aircraft in E,F and G airspace. That's why they don't have to state radio can, or can not be used in a safety case- because it's not a requirement in the first place!
ICAO makes it clear that radio is not required for VFR aircraft in E,F and G airspace. That's why they don't have to state radio can, or can not be used in a safety case- because it's not a requirement in the first place!
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Rather than just talk about E or G - the more pertinent point is Dick,
that E over D is less safe than C (or D)over D and costs the same at Broome and Karratha, so therefore its required to be promulgated as such.
The argument keeps being presented as a choice between E and G. This just muddies the water. When it is really a choice between G,E,D (or C or A, for that matter). So why would you choose E? What is the cost benefit?
More importantly if there is no cost/benefit for the vast majority of airspace users - wouldnt it be a culpable act to mandate a level of airspace that is less than the highest affordable level of airspace?
There is nothing inherently wrong with E airspace (in the right spot) but if you are offering me E or C at the same price (at Broome and Karratha) - I'll take the C thanks.
that E over D is less safe than C (or D)over D and costs the same at Broome and Karratha, so therefore its required to be promulgated as such.
The argument keeps being presented as a choice between E and G. This just muddies the water. When it is really a choice between G,E,D (or C or A, for that matter). So why would you choose E? What is the cost benefit?
More importantly if there is no cost/benefit for the vast majority of airspace users - wouldnt it be a culpable act to mandate a level of airspace that is less than the highest affordable level of airspace?
There is nothing inherently wrong with E airspace (in the right spot) but if you are offering me E or C at the same price (at Broome and Karratha) - I'll take the C thanks.
Dick,
Wow ... we're really getting into semantics now....
I think the "spirit" of the Law is that ... if you can't use transponders as a design element, then you surely shouldn't be using them as an implementation element ... especially in non-surveillance airspace.
Rubbish, ICAO has not stated that transponders cannot be used as a risk mitigator in safety studies in relation to airspace.
You CANNOT [yet], however, design a system that relies on aircraft-to-aircraft surveillance or separation based on the use of transponders – that is, the use of airborne collision avoidance systems, like TCAS and Mode A/C transponders, as an airspace design tool, is prohibited.
..... Effectively, ICAO – and the ANC specifically – has determined that ACAS MAY NOT be used as a risk mitigator under any circumstances in the design of airspace management procedures. ALL ICAO Technical Panels have been directed that they may not factor such systems in the development of separation standards, the design of procedures, or the development of future systems. ACAS is a “last line of defence” for pilots – NOT a system design tool.
ICAO ANNEX 11:
SECTION 2.4: DETERMINATION OF THE NEED FOR AIR TRAFFIC SERVICES
2.4.1 The need for the provision of air traffic services shall be determined by consideration of the following:
a. the types of air traffic involved;
b. the density of air traffic;
c. the meteorological conditions;
d. such other factors as may be relevant.
Note:- due to the number of elements involved, it has not been possible to develop specific data to determine the need for air traffic services in a given area or at a given location. For example:
a. a mixture of types of aircraft of varying speed (conventional jet, etc) might necessitate the provision of air traffic services, whereas a relatively greater density of traffic where only one type of operation is involved would not;
b. meteorological conditions might have considerable effect in areas where there is a constant flow of air traffic (e.g., scheduled traffic), whereas similar or worse meteorological conditions might be relatively unimportant in an area where air traffic would be discontinued is such conditions (e.g., local VFR flights);
c. open stretches of water, mountainous, uninhabited or desert areas might necessitate the provision of air traffic services even though the frequency of operations is extremely low.
2.4.2 The carriage of airborne collision avoidance systems (ACAS) by aircraft in a given area shall not be a factor in determining the need for air traffic services in that area.
..... Effectively, ICAO – and the ANC specifically – has determined that ACAS MAY NOT be used as a risk mitigator under any circumstances in the design of airspace management procedures. ALL ICAO Technical Panels have been directed that they may not factor such systems in the development of separation standards, the design of procedures, or the development of future systems. ACAS is a “last line of defence” for pilots – NOT a system design tool.
ICAO ANNEX 11:
SECTION 2.4: DETERMINATION OF THE NEED FOR AIR TRAFFIC SERVICES
2.4.1 The need for the provision of air traffic services shall be determined by consideration of the following:
a. the types of air traffic involved;
b. the density of air traffic;
c. the meteorological conditions;
d. such other factors as may be relevant.
Note:- due to the number of elements involved, it has not been possible to develop specific data to determine the need for air traffic services in a given area or at a given location. For example:
a. a mixture of types of aircraft of varying speed (conventional jet, etc) might necessitate the provision of air traffic services, whereas a relatively greater density of traffic where only one type of operation is involved would not;
b. meteorological conditions might have considerable effect in areas where there is a constant flow of air traffic (e.g., scheduled traffic), whereas similar or worse meteorological conditions might be relatively unimportant in an area where air traffic would be discontinued is such conditions (e.g., local VFR flights);
c. open stretches of water, mountainous, uninhabited or desert areas might necessitate the provision of air traffic services even though the frequency of operations is extremely low.
2.4.2 The carriage of airborne collision avoidance systems (ACAS) by aircraft in a given area shall not be a factor in determining the need for air traffic services in that area.
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Hi Dick,
As regards your Post #735, I admit to being a little confused. You stated that:
That was in response to Peuce.
Yet, at the same time you are perfectly willing to selectively quote the 'anonymous' VOR in support of your argument about Class E. And I emphasise 'selectively.'
'It doesn't compute Jim,'
Dick, Class E is a dog in the terminal environment and an accident waiting to happen.
What Class E does, in the terminal environment, is allow a situation where separation responsibility could rest on the shoulders of a minimum hours VFR pilot. Are you seriously telling me it's 'safe' and 'acceptable' for a VFR pilot with 5 hours under his belt to find, identify and self-separate from an aluminium tube doing 250 KIAS on descent? An aircraft that is not tracking by any feature the 5-hour VFR pilot is familiar with? An IFR aircraft that has 150 trusting, fare-paying punters down the back in the terminal area? And don't give me that stuff about the responsibility to 'look out the window.' Unalerted see-and-avoid,' in non-radar Class E terminal airspace, is dangerous and potentially fatal. In fact Class E terminal airspace in a surveilled environment isn't the duck's guts either. But that's a different argument.
I cannot believe what I see as your 'fundamentalist' views in relation to terminal Class E. It reminds me of those US born-again Christians. 'Hallelujah, praise the Lord and trust in God.'
That's about all the guarantee we have with non-radar Class E Dick - 'trust in God.'
Damn, he's gone again.
As regards your Post #735, I admit to being a little confused. You stated that:
What is amazing about this VOR stuff is that no-one is stating this information under their own name. Why could this be? Surely they wouldn’t be scared of giving factual information which is so important for our aviation community?
Yet, at the same time you are perfectly willing to selectively quote the 'anonymous' VOR in support of your argument about Class E. And I emphasise 'selectively.'
'It doesn't compute Jim,'
Dick, Class E is a dog in the terminal environment and an accident waiting to happen.
What Class E does, in the terminal environment, is allow a situation where separation responsibility could rest on the shoulders of a minimum hours VFR pilot. Are you seriously telling me it's 'safe' and 'acceptable' for a VFR pilot with 5 hours under his belt to find, identify and self-separate from an aluminium tube doing 250 KIAS on descent? An aircraft that is not tracking by any feature the 5-hour VFR pilot is familiar with? An IFR aircraft that has 150 trusting, fare-paying punters down the back in the terminal area? And don't give me that stuff about the responsibility to 'look out the window.' Unalerted see-and-avoid,' in non-radar Class E terminal airspace, is dangerous and potentially fatal. In fact Class E terminal airspace in a surveilled environment isn't the duck's guts either. But that's a different argument.
I cannot believe what I see as your 'fundamentalist' views in relation to terminal Class E. It reminds me of those US born-again Christians. 'Hallelujah, praise the Lord and trust in God.'
That's about all the guarantee we have with non-radar Class E Dick - 'trust in God.'
Damn, he's gone again.
Last edited by Howabout; 28th Apr 2010 at 11:11.
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Yes, I know G without a transponder requirement is OK at places like Broome and Ballina - but upgrade the airspace to E and add a mandatory transponder requirement and it suddenly becomes unsafe.
Get Real!
Get Real!
With respect to Broome at the moment yes it is Class G, and due to traffic density etc it has been declared in need of a Class D tower, so yes at the moment it is deemed NOT SAFE ENOUGH.
With Ballina it is clearly not reaching that level of Traffic, however if you wish to push the barrow for increased level of surveillence at many aerodromes (I recall an ADSB debate some time back) Class E to the ground would be welcome I am sure, and only then increased to D or C as the need arises.
E without radar/multilat/adsb is a waste of time.
If I get it.....why is it your friends do not get it.
SQ
Dick,
Get with the program, old chap. The mandatory CTAF is 30nm which covers VFR up to 10,000ft, pretty-well covering jet profiles inbound (even a nice man in the CAGRO there to talk to just like you've always wanted), then above it's mandatory transponders, just like in E. So yes, as much as you hate it, Australian G is safer than E because of the radio use requirement.
Your astounding lack of knowledge of the Aus NAS doesn't put you in a very credible position when you so vehemently want to change it.
Yes, I know G without a transponder requirement is OK at places like Broome and Ballina - but upgrade the airspace to E and add a mandatory transponder requirement and it suddenly becomes unsafe.
Get Real!
Get Real!
Your astounding lack of knowledge of the Aus NAS doesn't put you in a very credible position when you so vehemently want to change it.
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Dick,
Another one of your I understand/I believe comments with nothing to actually back it up.
Where is your reference?
Do you seriously believe that actual ATCs turn up at these meetings? When you were in charge of the CAA how many WORKFACE ATCs were involved in your decision making processes? How many managers (the ones you were really talking to) would care if workforce numbers were cut. I would think that in Management 101 they teach get the least number of workers doing the most amount of work.
This may be the reason there is a worldwide shortage of ATCs. Air Navigation Service Providers (ANSPs) and their organisation (CANSO) hope that the next 'latest piece of technology' will be the panacea to all their lack of recruiting.
Just maybe this ICAO decision you talk of was made on safety grounds. If you seriously think that ICAO decisions are made on such flimsy grounds how can you support ICAO Airspace Classifications?
Dick, you rabbit on about posting under ones own name and controllers only being interested in preserving their jobs. Yet on the Benalla thread you wanted controllers in Australia to provide a LSALT and Instrument Approach monitoring service under radar coverage. Do you still support this idea? We have less than 8% of the controllers they have in the States and vastly less surveillance coverage, yet you want us to provide a US style service. When will it sink in that you must compare apples with apples.
Another one of your I understand/I believe comments with nothing to actually back it up.
By the way, I understand the ruling in relation to transponders not being used as a safety mitigator came because a group of Air Traffic Controllers at an ICAO meeting were concerned in the early days that ACAS may replace Air Traffic Control. They naturally made their decision to preserve their jobs. Who wouldn’t?
Do you seriously believe that actual ATCs turn up at these meetings? When you were in charge of the CAA how many WORKFACE ATCs were involved in your decision making processes? How many managers (the ones you were really talking to) would care if workforce numbers were cut. I would think that in Management 101 they teach get the least number of workers doing the most amount of work.
This may be the reason there is a worldwide shortage of ATCs. Air Navigation Service Providers (ANSPs) and their organisation (CANSO) hope that the next 'latest piece of technology' will be the panacea to all their lack of recruiting.
Just maybe this ICAO decision you talk of was made on safety grounds. If you seriously think that ICAO decisions are made on such flimsy grounds how can you support ICAO Airspace Classifications?
Dick, you rabbit on about posting under ones own name and controllers only being interested in preserving their jobs. Yet on the Benalla thread you wanted controllers in Australia to provide a LSALT and Instrument Approach monitoring service under radar coverage. Do you still support this idea? We have less than 8% of the controllers they have in the States and vastly less surveillance coverage, yet you want us to provide a US style service. When will it sink in that you must compare apples with apples.
Checking at the time it was shown that the majority on the panel were from ATC.
I no longer have the info- perhaps you can prove me wrong by listing the names and their professions.
If you are going to do a proper safety study of airspace you have to include all factors. If you leave out ACAS you do not get the correct result.
Nowhere in ICAO documentation does it state that ACAS must be left out of safety studies.
Yes, I still support that we move forward with safety and offer a MSA service to IFR when in IMC in radar covered airspace. Happens in the USA and Canada and we have a similar wealth so why not.
We will do it after a jet hits a mountain close to Proserpine - so why not do it before the accident.
I no longer have the info- perhaps you can prove me wrong by listing the names and their professions.
If you are going to do a proper safety study of airspace you have to include all factors. If you leave out ACAS you do not get the correct result.
Nowhere in ICAO documentation does it state that ACAS must be left out of safety studies.
Yes, I still support that we move forward with safety and offer a MSA service to IFR when in IMC in radar covered airspace. Happens in the USA and Canada and we have a similar wealth so why not.
We will do it after a jet hits a mountain close to Proserpine - so why not do it before the accident.
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C, D verses E
This took me a while to find, so please take the time to consider it, I am out west in NSW so not much internet access.
From the CASA OAR YMAV study
Point 7
Similar documentary evidence appears in all recent airspace studies.
Who needs to get real?
SQ
This took me a while to find, so please take the time to consider it, I am out west in NSW so not much internet access.
From the CASA OAR YMAV study
1.4.3 The cost of the provision of a Class C air traffic control service is the same as that of a Class D or E service. However, the Class C service provides significantly greater risk mitigation to passenger transport aircraft against VFR aircraft threats than that provided by Class D and Class E.
The cost of provision of a Class C Aerodrome Control Service is the same as that of a Class D Aerodrome Control Service but the risk mitigation provided by a Class C service is significantly higher for IFR aircraft with respect to VFR aircraft. Similarly, the cost of provision of a Class C radar Approach Control Service is the same as that of a Class E service but the risk mitigation provided is significantly higher for IFR aircraft with respect to VFR aircraft.
Who needs to get real?
SQ
squawk6969,
Exactly. Talk of who was responsible for writing an ICAO rule is just a frivoulous red herring meal.
The status at the moment is:
That really only leaves one credible option ...
Exactly. Talk of who was responsible for writing an ICAO rule is just a frivoulous red herring meal.
The status at the moment is:
- Let's say the mathematicians have got it right, and Class E link airspace (at Broome) is "safe enough"
- That then triggers the next level of enquiry... "can a higher level of risk mitigation be provided .. at the same cost?"
- Most pundits ( including the quoted airspace reviews) say yes, C ( or D) could be provided at a similar cost.
That really only leaves one credible option ...
Dick,
If you didn't already know, the MSAWS is part of the FIS and can be provided by ATC in every type of airspace.
EGPWS is now fitted to all big machines. It does the job without human interference. If you are now going to tell the airlines they will have to fork out millions for extra ATC sectors to monitor and run the MSAWS as well, I expect they will not be happy. But hang on, that will be good for the ATC managers; more bonuses!
AsA changed the airspace back after the Launy airprox. Why are you trying to go back to E when the message is clear?
Using your words, "when Bloggs has a near miss (or worse) at Broome with a VFR overflying, not talking to anyone in E, we will change the airspace to C or D - so why not do it before the accident?".
Yes, I still support that we move forward with safety and offer a MSA service to IFR when in IMC in radar covered airspace. Happens in the USA and Canada and we have a similar wealth so why not.
We will do it after a jet hits a mountain close to Proserpine - so why not do it before the accident.
We will do it after a jet hits a mountain close to Proserpine - so why not do it before the accident.
EGPWS is now fitted to all big machines. It does the job without human interference. If you are now going to tell the airlines they will have to fork out millions for extra ATC sectors to monitor and run the MSAWS as well, I expect they will not be happy. But hang on, that will be good for the ATC managers; more bonuses!
AsA changed the airspace back after the Launy airprox. Why are you trying to go back to E when the message is clear?
Using your words, "when Bloggs has a near miss (or worse) at Broome with a VFR overflying, not talking to anyone in E, we will change the airspace to C or D - so why not do it before the accident?".
Owen Stanley
All you are showing by your Post #757 is just how utterly fixed in concrete your thinking is. I can assure you, a radar in a centre only requires one paint of an altitude below the LSA/MSA and it will set off the alarm if the pilot has not cancelled IFR.
You do everything you can to show that there’s no way we can offer a safer service at a place like Benalla. Well, you are wrong.
It’s the reason people like you are not used when decisions need to be made laterally looking at how to make improvements and changes with existing systems.
By the way, I don’t want you to monitor the approach to 1,090 feet – that’s impossible, considering the coverage of the radar. However, if the radar coverage is below the legal minimum safe LSA, I would prefer the alarm system to be enabled.
At Proserpine, the radar coverage from the centre goes well below the mountain tops in the aerodrome vicinity. However, if I remember correctly, pilots change off the radar frequency at 4,500 feet on descent and the alarm system is not enabled at the centre anyway.
Owen Stanley – concrete, concrete, concrete. I’ve encountered people like you for years. They were the ones who said we couldn’t possibly use international airworthiness standards and accept foreign airworthiness certificates from five leading countries.
They were wrong. We have saved tens of millions of dollars, and safety has not decreased in any way.
All you are showing by your Post #757 is just how utterly fixed in concrete your thinking is. I can assure you, a radar in a centre only requires one paint of an altitude below the LSA/MSA and it will set off the alarm if the pilot has not cancelled IFR.
You do everything you can to show that there’s no way we can offer a safer service at a place like Benalla. Well, you are wrong.
It’s the reason people like you are not used when decisions need to be made laterally looking at how to make improvements and changes with existing systems.
By the way, I don’t want you to monitor the approach to 1,090 feet – that’s impossible, considering the coverage of the radar. However, if the radar coverage is below the legal minimum safe LSA, I would prefer the alarm system to be enabled.
At Proserpine, the radar coverage from the centre goes well below the mountain tops in the aerodrome vicinity. However, if I remember correctly, pilots change off the radar frequency at 4,500 feet on descent and the alarm system is not enabled at the centre anyway.
Owen Stanley – concrete, concrete, concrete. I’ve encountered people like you for years. They were the ones who said we couldn’t possibly use international airworthiness standards and accept foreign airworthiness certificates from five leading countries.
They were wrong. We have saved tens of millions of dollars, and safety has not decreased in any way.
Now Dick you can call me a sceptic, mind set in concrete individual, thickwit or whatever , but after seeing the cockup with E in the Appe Isle I really cannot see the advantage of it can you? If it didn't work in the Apple Isle is it going to work in Broome?
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Mr Smith
Airworthiness and Airspace regulation have nothing in common. Nor does CTA/R services at Proserpine or elsewhere when RPT have EGPWS. Does your jet have TAWS or E/GPWS?
ICAO Doc 9863 - ACAS Manual- [Apologies in advance to LeadSled for the troublesome fact quoting].
The following are some 'relevant' quotes that point to why the direction exists in Annnex 11 [ACAS not a design mitigator] in the context of ACAS limitations in CTA, and its interactions with non-ACAS equipped transponding aircraft, which are pertinent to this Class E [particulalrly in VMC with Un-known VFR] airspace discussion.
Notwithstading the clear direction in Annex 11 [as quoted earlier], and considering the totality of Doc 9863, Aviation is far better off for having ACAS [particularly ACAS II and later variants] as a last line of defence in CTA/R. It is not designed to be [nor capable of being] the only line of defence against mode A/C TXPDR's in 'unknown' GA [VFR] aircraft.
Airworthiness and Airspace regulation have nothing in common. Nor does CTA/R services at Proserpine or elsewhere when RPT have EGPWS. Does your jet have TAWS or E/GPWS?
ICAO Doc 9863 - ACAS Manual- [Apologies in advance to LeadSled for the troublesome fact quoting].
The following are some 'relevant' quotes that point to why the direction exists in Annnex 11 [ACAS not a design mitigator] in the context of ACAS limitations in CTA, and its interactions with non-ACAS equipped transponding aircraft, which are pertinent to this Class E [particulalrly in VMC with Un-known VFR] airspace discussion.
3.2.4.1 When the pilot of an ACAS aircraft receives an RA and manoeuvres as advised, the ACAS aircraft will normally be able to avoid the intruding aircraft provided the intruder does not accelerate or manoeuvre so as to defeat the RA response of the ACAS aircraft.
3.2.4.2 If the intruding aircraft is equipped with ACAS, a coordination procedure is performed via the air-to-air Mode S data link to ensure that the ACAS RAs are compatible
3.17.3 Reduction in the risk of collision
3.17.3.1 Status of the logic risk ratio
3.17.3.1.1 The risk ratio calculated for the purposes of Annex 10, Volume IV, Chapter 4 is a measure of the performance of the logic and not the ACAS as a whole. For example, ACAS can prevent a collision by prompting the pilot to carry out a successful visual search for the intruder and it can fail because a track is not established or the pilot ignores the RA; these are aspects of the total system that are not reflected in the calculations required for Annex 10, Volume IV, Chapter 4.
3.17.3.1.2 When considering the relevance of the “logic risk ratio” figures calculated for Annex 10, Volume IV, Chapter 4 to operations or policy decisions, it might be helpful to regard them as solely the reliability that can be attached to RAs. They express the effect that following an RA will have on the immediate risk of collision when, at the time it is issued, the pilot has no information other than the RA on which to base a decision whether to follow the RA or ignore it. As a rough guide, the collision risk created by ACAS arises from following the RA so the logic risk ratio overstates this “induced risk ratio”; on the other hand, it also overstates the capability of ACAS to prevent collisions because of the many other failure modes in the total system.
3.17.3.3 Induced and unresolved risk
3.17.3.3.1 It is not sufficient to demonstrate that ACAS will prevent collisions that might occur in its absence. The risk that ACAS logic could cause collisions in otherwise safe circumstances must be fully considered, not least because in managed airspace the number of encounters potentially facing an induced risk greatly exceeds the number of near collisions.
3.17.4 Compatibility with ATM
3.17.4.1 Nuisance alert rate
3.17.4.1.1 ACAS is required to diagnose a risk of imminent collision on the basis of incomplete information. Furthermore, this information has to be independent of that providing the primary basis for aircraft separation. It follows that there will be alerts in encounters where, from an operational perspective, there would seem to be no risk of collision. Annex 10, Volume IV, Chapter 4 requires that these nuisance alerts be as infrequent as possible.
3.17.4.2 Compatible sense selection
The requirement in Annex 10, Volume IV, Chapter 4 is not intended to constrain the manner in which dangerous encounters are resolved, but rather is based on an appreciation that the majority of RAs are likely to be generated in encounters where there is no danger of collision. It places a statistical limit on the frequency with which ACAS disrupts ATC or the normal operation of the aircraft by inverting the vertical separation of two aircraft.
3.17.4.3 Deviations caused by ACAS
The restrictions on the deviations that may be caused by following RAs (as per Annex 10, Volume IV, Chapter 4) limit the disruption to normal aircraft operation as well as to ATC. While deviations from altitude clearances are the most obviously disruptive to ATC, other deviations, such as that caused by an RA to climb when the aircraft is descending, could be viewed equally seriously by ATC.
4.1.2.2 ACAS is designed to minimize the unnecessary alert rate when the standard vertical separation is 1 000 ft below FL 420. When a smaller separation standard is used, unnecessary RAs may occur; for example, when providing 500 ft separation against VFR traffic or allowing visual clearances through the level of other traffic.
4.2 INDEPENDENCE OF ACAS THRESHOLDS FROM ATC SEPARATION STANDARDS
ACAS thresholds are independent from ATC separation standards because ACAS does not strive to ensure separation, which is ATC’s role, but tries to avoid collision as a last resort.
5.5.4 Encounter Type 3 — Manoeuvring based on visual acquisition
5.5.4.1 A B747 and a DC10 were flying on converging tracks and both were mistakenly cleared to FL 370. When the controller detected the mistake, he attempted to reclear the DC10 to FL 350. In attempting to resolve this conflict, the controller used an incorrect callsign/flight number for the DC10.
5.5.4.2 The B747 pilot wrongly took the clearance meant for the DC10 and initiated a descent. At the same time, the B747 ACAS issued a Climb RA. However, the B747 pilot decided to not follow the RA because the B747 had visually acquired the DC10 and the descent was continued.
5.5.4.3 The DC10 pilot, who also had the B747 in sight, received a Descend RA that was followed. At the last moment, the DC10 pilot arrested the descent upon perceiving that the B747 was at the same altitude and also descending. Also at the last moment, the B747 pilot performed a sudden and violent escape manoeuvre that injured a number of passengers and flight attendants.
5.5.4.4 Because of the inappropriate manoeuvre based on visual acquisition, the B747 passed 10 metres below the DC10 with no lateral separation.
8.1.4 Calculation of risk ratio
8.1.4.1 Unresolved and induced risk of collision
8.1.4.1.1 When simulating the ACAS II logic on the generated encounters, two cases can occur which have an adverse contribution to the risk ratio:
a) the encounter presents a risk of collision and the ACAS II resolution fails to avoid it. This is an unresolved risk of collision; and
b) the encounter does not present a risk of collision and the ACAS II resolution creates it. This is an induced risk of collision.
8.1.4.1.2 Note that the induced risk of collision may become an important factor in the residual risk of collision. In other words, in airspaces in which ACAS has substantially reduced the overall risk of collision, when a collision does occur, it is possible that ACAS will be a causal factor in that collision.
10.3.5 General aviation monitoring
10.3.5.1 General aviation aircraft equipped with Mode A/C transponders were monitored for altitude reporting accuracy. Twenty-one of 548 transponders reported altitudes that deviated by more than 200 ft from the correct altitude. This reinforces the need for ongoing maintenance of transponders and monitoring of transponder performance while operating in the airspace.
3.2.4.2 If the intruding aircraft is equipped with ACAS, a coordination procedure is performed via the air-to-air Mode S data link to ensure that the ACAS RAs are compatible
3.17.3 Reduction in the risk of collision
3.17.3.1 Status of the logic risk ratio
3.17.3.1.1 The risk ratio calculated for the purposes of Annex 10, Volume IV, Chapter 4 is a measure of the performance of the logic and not the ACAS as a whole. For example, ACAS can prevent a collision by prompting the pilot to carry out a successful visual search for the intruder and it can fail because a track is not established or the pilot ignores the RA; these are aspects of the total system that are not reflected in the calculations required for Annex 10, Volume IV, Chapter 4.
3.17.3.1.2 When considering the relevance of the “logic risk ratio” figures calculated for Annex 10, Volume IV, Chapter 4 to operations or policy decisions, it might be helpful to regard them as solely the reliability that can be attached to RAs. They express the effect that following an RA will have on the immediate risk of collision when, at the time it is issued, the pilot has no information other than the RA on which to base a decision whether to follow the RA or ignore it. As a rough guide, the collision risk created by ACAS arises from following the RA so the logic risk ratio overstates this “induced risk ratio”; on the other hand, it also overstates the capability of ACAS to prevent collisions because of the many other failure modes in the total system.
3.17.3.3 Induced and unresolved risk
3.17.3.3.1 It is not sufficient to demonstrate that ACAS will prevent collisions that might occur in its absence. The risk that ACAS logic could cause collisions in otherwise safe circumstances must be fully considered, not least because in managed airspace the number of encounters potentially facing an induced risk greatly exceeds the number of near collisions.
3.17.4 Compatibility with ATM
3.17.4.1 Nuisance alert rate
3.17.4.1.1 ACAS is required to diagnose a risk of imminent collision on the basis of incomplete information. Furthermore, this information has to be independent of that providing the primary basis for aircraft separation. It follows that there will be alerts in encounters where, from an operational perspective, there would seem to be no risk of collision. Annex 10, Volume IV, Chapter 4 requires that these nuisance alerts be as infrequent as possible.
3.17.4.2 Compatible sense selection
The requirement in Annex 10, Volume IV, Chapter 4 is not intended to constrain the manner in which dangerous encounters are resolved, but rather is based on an appreciation that the majority of RAs are likely to be generated in encounters where there is no danger of collision. It places a statistical limit on the frequency with which ACAS disrupts ATC or the normal operation of the aircraft by inverting the vertical separation of two aircraft.
3.17.4.3 Deviations caused by ACAS
The restrictions on the deviations that may be caused by following RAs (as per Annex 10, Volume IV, Chapter 4) limit the disruption to normal aircraft operation as well as to ATC. While deviations from altitude clearances are the most obviously disruptive to ATC, other deviations, such as that caused by an RA to climb when the aircraft is descending, could be viewed equally seriously by ATC.
4.1.2.2 ACAS is designed to minimize the unnecessary alert rate when the standard vertical separation is 1 000 ft below FL 420. When a smaller separation standard is used, unnecessary RAs may occur; for example, when providing 500 ft separation against VFR traffic or allowing visual clearances through the level of other traffic.
4.2 INDEPENDENCE OF ACAS THRESHOLDS FROM ATC SEPARATION STANDARDS
ACAS thresholds are independent from ATC separation standards because ACAS does not strive to ensure separation, which is ATC’s role, but tries to avoid collision as a last resort.
5.5.4 Encounter Type 3 — Manoeuvring based on visual acquisition
5.5.4.1 A B747 and a DC10 were flying on converging tracks and both were mistakenly cleared to FL 370. When the controller detected the mistake, he attempted to reclear the DC10 to FL 350. In attempting to resolve this conflict, the controller used an incorrect callsign/flight number for the DC10.
5.5.4.2 The B747 pilot wrongly took the clearance meant for the DC10 and initiated a descent. At the same time, the B747 ACAS issued a Climb RA. However, the B747 pilot decided to not follow the RA because the B747 had visually acquired the DC10 and the descent was continued.
5.5.4.3 The DC10 pilot, who also had the B747 in sight, received a Descend RA that was followed. At the last moment, the DC10 pilot arrested the descent upon perceiving that the B747 was at the same altitude and also descending. Also at the last moment, the B747 pilot performed a sudden and violent escape manoeuvre that injured a number of passengers and flight attendants.
5.5.4.4 Because of the inappropriate manoeuvre based on visual acquisition, the B747 passed 10 metres below the DC10 with no lateral separation.
8.1.4 Calculation of risk ratio
8.1.4.1 Unresolved and induced risk of collision
8.1.4.1.1 When simulating the ACAS II logic on the generated encounters, two cases can occur which have an adverse contribution to the risk ratio:
a) the encounter presents a risk of collision and the ACAS II resolution fails to avoid it. This is an unresolved risk of collision; and
b) the encounter does not present a risk of collision and the ACAS II resolution creates it. This is an induced risk of collision.
8.1.4.1.2 Note that the induced risk of collision may become an important factor in the residual risk of collision. In other words, in airspaces in which ACAS has substantially reduced the overall risk of collision, when a collision does occur, it is possible that ACAS will be a causal factor in that collision.
10.3.5 General aviation monitoring
10.3.5.1 General aviation aircraft equipped with Mode A/C transponders were monitored for altitude reporting accuracy. Twenty-one of 548 transponders reported altitudes that deviated by more than 200 ft from the correct altitude. This reinforces the need for ongoing maintenance of transponders and monitoring of transponder performance while operating in the airspace.
Last edited by ARFOR; 29th Apr 2010 at 09:42. Reason: formatting
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Over run
You talk of "the lowest common denominator of unalerted se and avoid, GA."
Small aircraft in outback Australia have been using the unalerted see and avoid sucessfully for decades. I don't think they are the "lowest common denominator." 80% of the country depends on GA for essential transport and the real people who live out there do not consider them the "lowest common denominator." City slickers might.
There are thousands of aircraft out there doing what the airlines cannot do.
You have offended lots of valuable, competent aviators.
Small aircraft in outback Australia have been using the unalerted see and avoid sucessfully for decades. I don't think they are the "lowest common denominator." 80% of the country depends on GA for essential transport and the real people who live out there do not consider them the "lowest common denominator." City slickers might.
There are thousands of aircraft out there doing what the airlines cannot do.
You have offended lots of valuable, competent aviators.
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Bushy
I don't think there would be too many people around who underestimated nor appreciated the job performed by Australian bush pilots. However, what OverRun actually said was:-
I read that to be a concern regarding the 'lowest common denominator procedure', rather than a reflection of the standard of the GA pilots concerned. 
I don't think there would be too many people around who underestimated nor appreciated the job performed by Australian bush pilots. However, what OverRun actually said was:-
There is no safety case for this, no modelling, no justification, and no cost saving. But a big step backwards as airline and RPT mix it up with the lowest common denominator of unalerted see-and-avoid GA.
Last edited by ARFOR; 29th Apr 2010 at 08:55. Reason: formatting