Busting CAS, no altitude.
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Busting CAS, no altitude.
In this clip some GA plane busts Heathrow's class A and they divert the jets away from him. The GA plane is squawking 7000 but has no mode C or hasn't turned it on.
My question is twofold:
1. Do you see his altitude on your primary return on the radar?
2. If you don't see altitude, are you relying on the mode C return solely for altitude? Because a mode C return can obviously be altered and be incorrect - I've many times flown with them being well off or have the wrong pressure altitude input.
How does this work?
My question is twofold:
1. Do you see his altitude on your primary return on the radar?
2. If you don't see altitude, are you relying on the mode C return solely for altitude? Because a mode C return can obviously be altered and be incorrect - I've many times flown with them being well off or have the wrong pressure altitude input.
How does this work?
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1. Do you see his altitude on your primary return on the radar?
2. If you don't see altitude, are you relying on the mode C return solely for altitude? Because a mode C return can obviously be altered and be incorrect - I've many times flown with them being well off or have the wrong pressure altitude input.
Vertical separation can only be applied using mode C on verified levels.
Traffic parameters are 2000ft if the level is unverified. So even if you had a unverfied VFR showing 1900ft difference in levels, traffic would still be passed.
This is a little bit unusual however, any aircraft in that situation should have a clearance, so either will have verified level information or be reporting levels. If this was a class E issue, it would be a completely different story.
However, if they have busted CTA are you still required to separated? Honestly I'm not too sure if you had to, cant remember anything in the books about it, I know I would still separate, as they do in the video.
However you can't use the mode c for separating vertically even if it is showing, as it is unverified. So they could have 6000ft vertically but not technically have a standard.
Do you still turn them with 6000ft? 4000ft? 2000ft?
Edit: Should add, its a situation that applies more to approach controllers, as CTA goes down to the ground near aerodromes, and further out you would have class E/G beneath. In that situation, a paint without mode C can be assumed to be OCTA/traffic issues. If they had mode C inside CTA, again, do you seperate with x ft between them.
Last edited by mikethepomme; 10th Sep 2011 at 03:40.
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Originally Posted by AdamFrisch
My question is twofold:
1. Do you see his altitude on your primary return on the radar?
2. If you don't see altitude, are you relying on the mode C return solely for altitude? Because a mode C return can obviously be altered and be incorrect - I've many times flown with them being well off or have the wrong pressure altitude input.
How does this work?
1. Do you see his altitude on your primary return on the radar?
2. If you don't see altitude, are you relying on the mode C return solely for altitude? Because a mode C return can obviously be altered and be incorrect - I've many times flown with them being well off or have the wrong pressure altitude input.
How does this work?
2. Mode C is used for vertical reference. Mode C provides altitude information from encoded altimeters. The altitude is encoded at 1013.2 Hpa. It is unaffected by subscale setting. The ATSU will convert the display as required eg. by inputting QNH to display altitudes below the TA. Yes, sometimes altitude encoders send information out of tolerance (which I recall is +/- 200ft) hence ATC endeavours to avoid unknown traffic by a minimum 5nm or 5000ft because intentions and Mode C accuracy are unknown.
Heathrow CTR busts cause carnage - huge increase in workload, huge delays, expense and waste of time and fuel, and are a serious risk to flight safety, hence zone-busters are not at all popular. The Controlled Airspace Incursion Tool highlights intruders in order to provide a bit of early warning.
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In the UK and under a radar control service I must seek to achieve the required minima against unknown traffic, even if the aircraft concerned reports the unknown traffic in sight. It is accepted that the minima may not be achieved against an unknown aircraft but all reasonable endeavours shall be made. We can use vertical if the mode C is showing, verified or not, but have to have 5000 feet and in the case of unverified mode C the radar returns must not merge.
Incidentally, I don't think you can change the mode C output of the transponder as it is encoded from a pressure of 1013 mbar/hectopascal regardless of the pressure set on your altimeter. (Admittedly it may be malfunctioning, hence the verification checks.) Below the transition level, my radar makes the necessary calculations based on our QNH to convert the displayed level into an altitude. This is displayed as e.g. A030 and for a flight level it will show e.g. F140. If you don't have mode C it shows ???? where the level would normally be.
Edit: Talkdownman can obviously type faster than me!
Incidentally, I don't think you can change the mode C output of the transponder as it is encoded from a pressure of 1013 mbar/hectopascal regardless of the pressure set on your altimeter. (Admittedly it may be malfunctioning, hence the verification checks.) Below the transition level, my radar makes the necessary calculations based on our QNH to convert the displayed level into an altitude. This is displayed as e.g. A030 and for a flight level it will show e.g. F140. If you don't have mode C it shows ???? where the level would normally be.
Edit: Talkdownman can obviously type faster than me!
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1 - As mike says, primary returns would show just an indication of something at that location, no altitude or code. In the video you actually see the infringing aircraft with an SSR return (mode A 7000, a conspicuity code which broadly means 'not receiving an ATS', with no mode C data).
2 - You probably need to think about this from a different perspective. For a controller, amongst other differentiations, a flight is either 'known traffic' or 'unknown traffic'.
Known traffic means that the controller knows about a particular aircraft and what it is going to do. It may seem strange but it doesn't mean that the aircraft is talking to that controller, in some cases the controller may have been told that the aircraft squawking XXXX wants to fly through a particular piece of airspace that he/she is responsible for at 3000ft and has agreed to it. This is known as co-ordination.
Unknown traffic is simply a flight that the controller has no knowledge of. In a radar environment one example is the infringing aircraft, which the controller can see is there but it doesn't have a clearance. If the aircraft is showing a level that is above or below the airspace for which the controller is responsible then he/she can assume that it is outside the airspace unless there is any information to suggest that the level information is not reliable. Because the controller doesn't know if the level information has been checked, in this situation there is a margin for error built into the procedures.
In the UK the rules for controllers about what to do if there is unknown traffic in airspace that they are looking after depend on the class of airspace in question. In the video you were looking at the Heathrow area which is class A and the rules say ' If radar derived, or other information, indicates that an aircraft is making an unauthorised penetration of the airspace, is lost, or has experienced radio failure avoiding action shall be given and traffic information shall be passed' - which is pretty much what you saw (the avoiding action bit, at least).
The comment - Because a mode C return can obviously be altered and be incorrect - I've many times flown with them being well off or have the wrong pressure altitude input - is based on an incorrect assumption I'm afraid. The level information contained in an SSR return is derived from a completely separate sensor from those the pilot is using and is always 'set' to 1013 hPa. It doesn't matter what setting the altimeter sub-scale is turned to, the mode C data will always show the level based on 1013 hPa. The radar display systems used by controllers will convert this information to show an altitude if this is necessary - if you do a search you'll find lots of posts on this particular topic and how it all works.
No doubt others will have typed faster than me but I hope this helps to explain things.
2 - You probably need to think about this from a different perspective. For a controller, amongst other differentiations, a flight is either 'known traffic' or 'unknown traffic'.
Known traffic means that the controller knows about a particular aircraft and what it is going to do. It may seem strange but it doesn't mean that the aircraft is talking to that controller, in some cases the controller may have been told that the aircraft squawking XXXX wants to fly through a particular piece of airspace that he/she is responsible for at 3000ft and has agreed to it. This is known as co-ordination.
Unknown traffic is simply a flight that the controller has no knowledge of. In a radar environment one example is the infringing aircraft, which the controller can see is there but it doesn't have a clearance. If the aircraft is showing a level that is above or below the airspace for which the controller is responsible then he/she can assume that it is outside the airspace unless there is any information to suggest that the level information is not reliable. Because the controller doesn't know if the level information has been checked, in this situation there is a margin for error built into the procedures.
In the UK the rules for controllers about what to do if there is unknown traffic in airspace that they are looking after depend on the class of airspace in question. In the video you were looking at the Heathrow area which is class A and the rules say ' If radar derived, or other information, indicates that an aircraft is making an unauthorised penetration of the airspace, is lost, or has experienced radio failure avoiding action shall be given and traffic information shall be passed' - which is pretty much what you saw (the avoiding action bit, at least).
The comment - Because a mode C return can obviously be altered and be incorrect - I've many times flown with them being well off or have the wrong pressure altitude input - is based on an incorrect assumption I'm afraid. The level information contained in an SSR return is derived from a completely separate sensor from those the pilot is using and is always 'set' to 1013 hPa. It doesn't matter what setting the altimeter sub-scale is turned to, the mode C data will always show the level based on 1013 hPa. The radar display systems used by controllers will convert this information to show an altitude if this is necessary - if you do a search you'll find lots of posts on this particular topic and how it all works.
No doubt others will have typed faster than me but I hope this helps to explain things.
Adam
Looking at your original questions, I am not sure of the relevance of the video clip. In that specific example, avoiding action had to be taken because there was no height information and the aircraft was observed to be within CAS, that part being the control zone, i.e. from surface level upwards.
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Looking at your original questions, I am not sure of the relevance of the video clip. In that specific example, avoiding action had to be taken because there was no height information and the aircraft was observed to be within CAS, that part being the control zone, i.e. from surface level upwards.
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Thanks for your explanations.
I'm just a little baffled that the radars used can't derive altitude. Had they been able to, then maybe a CAS bust without mode C, as in this case, would cause much less interruption. Surely a modern radar must be technically able to do this?
I'm just a little baffled that the radars used can't derive altitude. Had they been able to, then maybe a CAS bust without mode C, as in this case, would cause much less interruption. Surely a modern radar must be technically able to do this?
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Surely a modern radar must be technically able to do this?
We had once in France (last year, IIRC) an aircraft with a false altitude report (mode C).
When the pilot said he wasn't sure about his real altitude (FL 270 ?), controller asked the military for a check. They used their primary radar and said the actual level was between 250 and 290.
Great approximation, surely precise enough to lead an interceptor to a target : the plane was actually at FL 290, which was confirmed by a passing-by traffic who had to avoid it at the last second.
Modern technology radars are very precise : they were right in their calculation based on primary (
), but this is not enough to provide any vertical separation, ATCwise. As there is a doubt, the result is inevitably a lateral avoidance clearance.
A primary radar can be designed with stacked beams which can give a broad indication of the level band of a target; also, a specialist height finder primary radar, which scans verically in one direction at a time, could do the same thing. However, there is just no good reason for the expenditure on that sort of equipment in civil ATC, even if it could be obtained, and it would only be of very limited value as rather large minima for avoidance would have to be specified due to the radar tolerance and the aircraft's unknown intentions.
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If you have seen the MayDay series (if not, I really recommend it) there was one chapter about the Aeroperú 603 crash. Let me quote from the wiki
This stuck to me as the most vivid reminder that ATC can not obtain the altitude independently of the airplane's instruments (other than, as previously stated, an aproximation by the military)
As a result of the blocked static ports, the basic flight instruments relayed false airspeed, altitude and vertical speed data. Because the failure was not in any of the instruments but rather in a common supporting system, thereby defeating redundancy, the altimeter also relayed the false altitude information to the Air Traffic Controller, who was attempting to provide the pilots with basic flight data.
Even though an aircrafts transponder is always set at 1013.2hPa, errors can still occur by the pilot selecting the wrong QNH. This is because the pilot won't actually be at the altitude he thinks he is.
eg. on a ICAO SA day where a pilot is flying at A050 indicated but has incorrectly set 993 QNH, the aircraft will be at 5,600ft which, provided there are no techical issues, is what the controller will see on the RADAR. This is obviously out of tolerance but can be fixed by setting the correct QNH and descending to A050
PS. I hope my maths are correct
eg. on a ICAO SA day where a pilot is flying at A050 indicated but has incorrectly set 993 QNH, the aircraft will be at 5,600ft which, provided there are no techical issues, is what the controller will see on the RADAR. This is obviously out of tolerance but can be fixed by setting the correct QNH and descending to A050
PS. I hope my maths are correct
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but have to have 5000 feet
I note an aircraft doesn't have to squawk mode C under the TMA and is already deemed to be below 2500ft.
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AlanM:
Indeed. But it's worse than that. Aircraft with no Mode anything - primary returns only - can be directly overflown even though the controller has no information whatsoever on whether the aircraft concerned is at 6 ft, 66,000 ft, or anywhere in between. They're also deemed to be below controlled airspace. I've always thought it's an entirely bonkers practice, but it's done every day of the week at Heathrow and everywhere else, and of course these airports would be closed down if you didn't allow this "deeming".
Not sure what you mean by that - care to elaborate?
NS
Aircraft at the base of CAS at 2450ft with Mode C can be overflown at 3000ft legally as they are deemed to be outside CAS
to be fair, it is more pragmatic now, in terms of 'loss of separation' stats
NS
