Radar information - what's the altitude?
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When passing traffic information, the Mil only refer to traffic being "At" a level, altitude or height, when that traffic has been co-ordinated or under the control of the same controller and the Mode C has been verified. With regards to the original post, by inputting the regional QNH into the radar every hour, Mode Cs below the Tansition Altitude are calculated by the computer to the same QNH and displayed as an altitude, ie A30. When aircraft climb/descend through the TA, the Mode C will adjust on the display to a 1013 conversion. Therefore, during periods of high/low pressure, an aircraft displaying FL060 can in fact be at the same level/altitude as an aircraft at 5500 ft on the regional QNH.
When passing traffic information, the Mil only refer to traffic being "At" a level, altitude or height, when that traffic has been co-ordinated or under the control of the same controller and the Mode C has been verified.
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basically - yes. Obviously unknown A/c squawking 7000 with mode C will by definition be unverified (also referred to as "indicating") because you're not talking to the pilot to effect verification!
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"I might identify the aircraft on the 7000 squawk"
Interesting idea Spitoon,
what method of ident would you use...not a secondary method I hope?
'Good Book' page 1-5-6 para
4.1.c) Observing an IDENT feature when it has been requested... Aircraft
displaying the conspicuity code are not to be identified by this method.
Interesting idea Spitoon,
what method of ident would you use...not a secondary method I hope?
'Good Book' page 1-5-6 para
4.1.c) Observing an IDENT feature when it has been requested... Aircraft
displaying the conspicuity code are not to be identified by this method.
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For RAC/OPs.
If an acft is wearing a validated mode 3A code then the mode c displayed is deemed by other viewers as verified - so the mil would describe its level as "AT" even without coordination. If the controller working that traffic notices an error in the acfts mode C it is normally turned off - unless mode C and A are linked as in some older kit and cant be turned off without also turning off the Squawk. Then the controller should pass the word down the line to adjacent units/ viewers that the mode c is corrupt.
DogGone
If an acft is wearing a validated mode 3A code then the mode c displayed is deemed by other viewers as verified - so the mil would describe its level as "AT" even without coordination. If the controller working that traffic notices an error in the acfts mode C it is normally turned off - unless mode C and A are linked as in some older kit and cant be turned off without also turning off the Squawk. Then the controller should pass the word down the line to adjacent units/ viewers that the mode c is corrupt.
DogGone
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Well I must admit that it is a bit more complicated than I had thought! I do dislike being told that an aircraft is "2000 ft below" when I am in descent, because I suspect that I was higher the last time the ATCO looked at me on her radar screen, and therefore the other aircraft isn't 2000 ft lower at all.
It is the uncertainty that I don't like, and I'd certainly feel happier if I was told that the aircraft was "at 3000 ft" whether verified, unverified, or "at". Then I would feel I knew where it was, +/- 200 ft or so.
However I am not knocking the service, which is usually very good and only making a pilot's subjective comment. Not many other pilots have joined in with my view, so maybe it is not widely held.
I do feel that we sometimes make quite odd changes to the way things are said because "something once happened". I know we have to learn from experience, but I feel we do rather overdo it at times.
It is the uncertainty that I don't like, and I'd certainly feel happier if I was told that the aircraft was "at 3000 ft" whether verified, unverified, or "at". Then I would feel I knew where it was, +/- 200 ft or so.
However I am not knocking the service, which is usually very good and only making a pilot's subjective comment. Not many other pilots have joined in with my view, so maybe it is not widely held.
I do feel that we sometimes make quite odd changes to the way things are said because "something once happened". I know we have to learn from experience, but I feel we do rather overdo it at times.
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Not if you want to remain in VMC and levelling off would involve entering cloud. If I was in that position I would seriously consider requesting a RAS cos I would have lost all possibility of seeing the traffic.
NS
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Whilst all in favour of clear, concise and helpful R/T the problem comes when reported height information is based solely on SSR Mode C. I think the verified/unverified part is a red herring - the following applies whether verified of not.
As many above may have already said, the Controller is using a display where all Mode C information is converted to the same pressure setting(s). It is therefore deemed better for the Controller to relay relative height information than the observed height readout.
For example: Let's assume you're in receipt of RIS, decending through 2800' to 2000' on an QNH of 983mbs. The controller has unknown traffic indicating 3000' on the display. This height readout has been corrected to the SAS so is actually reading 900' high (1013-983 = 30. 30x30=900). If you were told the a/c was at 3000' you might be fooled into thinking "I'm below that and descending, it isn't a factor", whereas in truth you're still descending towards the other traffic.
To avoid this situation therefore, the Controller should compare your SSR height read-out (that has also been converted) with that of the other a/c and only pass relative height information i.e. "indicating 700' below you". True there will be a minor time-lag due to SSR data-transmission/display update rates/RT time - but ISTM that is still safer than giving a completely false impression?
As many above may have already said, the Controller is using a display where all Mode C information is converted to the same pressure setting(s). It is therefore deemed better for the Controller to relay relative height information than the observed height readout.
For example: Let's assume you're in receipt of RIS, decending through 2800' to 2000' on an QNH of 983mbs. The controller has unknown traffic indicating 3000' on the display. This height readout has been corrected to the SAS so is actually reading 900' high (1013-983 = 30. 30x30=900). If you were told the a/c was at 3000' you might be fooled into thinking "I'm below that and descending, it isn't a factor", whereas in truth you're still descending towards the other traffic.
To avoid this situation therefore, the Controller should compare your SSR height read-out (that has also been converted) with that of the other a/c and only pass relative height information i.e. "indicating 700' below you". True there will be a minor time-lag due to SSR data-transmission/display update rates/RT time - but ISTM that is still safer than giving a completely false impression?
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Pierre
I believe you're 1/2 right...the levels shown on the screen ARE transmitted on 1013.2 AND converted to the same datum (below TA) which will be whatever is input into your radar display/system.
Some use 1013 (scary) and some input their local QNH. If QNH is input, and we are talking at or below TA (which in your example of 3000' you are), then unlike in your example, the mode C readout will be relevant, i.e. 2800ft descending will be below unknown traffic @ 3000ft...and better still, this will be based on 1013.2 set in the encoding altimeter and not dependent on the pressure set by the pilot on the sub-scale. WYSIWYG
I believe you're 1/2 right...the levels shown on the screen ARE transmitted on 1013.2 AND converted to the same datum (below TA) which will be whatever is input into your radar display/system.
Some use 1013 (scary) and some input their local QNH. If QNH is input, and we are talking at or below TA (which in your example of 3000' you are), then unlike in your example, the mode C readout will be relevant, i.e. 2800ft descending will be below unknown traffic @ 3000ft...and better still, this will be based on 1013.2 set in the encoding altimeter and not dependent on the pressure set by the pilot on the sub-scale. WYSIWYG
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With regard to the "Traffic XXX feet above/below you", the useful part of it for VMC flight is the "above/below". Over the years I've had plenty of controllers say: "Traffic below you in your 10 o'clock". So long as you know to look up or down, and vaguely what direction to gaze in, you're most of the way to spotting it.
David C
David C
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torichelli is, I suggest, being a bit pedantic - factually correct but over emphasising the wrong point - let's take it up a couple of thousand from 3000 to FL50? (In my expereince I have never seen/worked at a unit that inputs QNH on the grounds that it is inviting an input error - but that's not to say there aren't units that do?)
DScartwright has hit the nail - such traffic information includes advisory height information, it isn't going to be spot on accurate! all that is surely important is a guide whether to look above, well above/ below, well below?
DScartwright has hit the nail - such traffic information includes advisory height information, it isn't going to be spot on accurate! all that is surely important is a guide whether to look above, well above/ below, well below?
"I think the verified/unverified part is a red herring"
(Still can't get the "blue panel" quote system to work!)
Hardly a red herring - the inclusion of "unverified" in the case of most unknown traffic is saying that there is a chance that the height information could be completely wrong.
(Still can't get the "blue panel" quote system to work!)
Hardly a red herring - the inclusion of "unverified" in the case of most unknown traffic is saying that there is a chance that the height information could be completely wrong.
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the inclusion of "unverified" in the case of most unknown traffic is saying that there is a chance that the height information could be completely wrong
(Politely) Get back in your shed - either of them!
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Pierre
"In my experience I have never seen/worked at a unit that inputs QNH"...in 4 units over 21 (radar) years, that's the only kit I've ever worked with
"DScartwright has hit the nail - such traffic information includes advisory height information, it isn't going to be spot on accurate! all that is surely important is a guide whether to look above, well above/ below, well below?"...isn't that what the standard phrase for unknown traffic in the MATS Pt1 says? as per my original post on this thread?
Tori
"In my experience I have never seen/worked at a unit that inputs QNH"...in 4 units over 21 (radar) years, that's the only kit I've ever worked with
"DScartwright has hit the nail - such traffic information includes advisory height information, it isn't going to be spot on accurate! all that is surely important is a guide whether to look above, well above/ below, well below?"...isn't that what the standard phrase for unknown traffic in the MATS Pt1 says? as per my original post on this thread?
Tori
