Radar information - what's the altitude?
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Radar information - what's the altitude?
When being given an RIS, I don't like the current practice of advising aircraft that they have conflicting traffic at (for instance) 10 o'clock "2500ft below" or "1500 ft above". 2500 ft below isn't very helpful to me when I am descending, because I have to do some arithmetic and by the time my slow brain has worked it out I am probably 1000 ft closer to the traffic than I was! I'd rather be told that it is at a particular altitude - "3000 ft", so that I can quickly and easily picture where the traffic is, and assess the significance.
Why did the practice change?
Why did the practice change?
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As far as I know, there were some instances where people were mistaking that as an instruction to climb/descend to that altitude, so they changed it soay it was a certain number of feet above/below. Im sure someone can confirm/correct me...
DF
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You what??
As an PPL IMC Holder for 12 years and a current ATC for 6 years, we tell you what it is on our screens! Under RIS i should remind you are responsible for your own separation! And why would I know what pressure setting say a 7000 squawk was under? can only go on what the screen tells us!! Do you want me to fly the plane for you?
NM
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Why did the practice change?
It hasn't . If in doubt ask the ATCO to give you the contacts level , be it verified or unverified
And why would I know what pressure setting say a 7000 squawk was under?
neilmac
Isn't the altitude displayed dependent on the pressure set in the equipment, therefore what the A/c has set is irrelevant?
Any way under the proposed changes all you might get in future will be
"
, that looked close "
It hasn't . If in doubt ask the ATCO to give you the contacts level , be it verified or unverified
And why would I know what pressure setting say a 7000 squawk was under?
neilmac
Isn't the altitude displayed dependent on the pressure set in the equipment, therefore what the A/c has set is irrelevant?
Any way under the proposed changes all you might get in future will be
"
, that looked close "
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As NM says the current hourly regional QNH should be typed into the radar database. All acft flying away from the circuit below the TA would be on this If memory serves me corectly, the controller will then see an altitude relevant to that setting. Cant remember exactly how the computer assimilated the altitude of acft above this. I think that what you saw was always displayed relative to the QNH value entered just that above 3000, the altitude had a 0 put in front of it to show a FL?
Anyone??
As to whether its verified or not the give away used to be in the ATC phraseology. If the conflicting traffic was wearing a known SSR code then its vertical position would be described to you using the term :
" ....AT 3000 etc"
If however the SSR was unknown i.e 7000 then the term :
"... INDICATING 3000 etc" was used.
Was 10 years ago though so things in the UK (MIL) may have changed.
DogGone
Anyone??
As to whether its verified or not the give away used to be in the ATC phraseology. If the conflicting traffic was wearing a known SSR code then its vertical position would be described to you using the term :
" ....AT 3000 etc"
If however the SSR was unknown i.e 7000 then the term :
"... INDICATING 3000 etc" was used.
Was 10 years ago though so things in the UK (MIL) may have changed.
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Originally Posted by neilmac
Your right radar set on 1013mbs, I have PM 'd Riverboat to explain!
Originally Posted by BurglarsDog
All acft flying away from the circuit below the TA would be on this If memory serves me corectly, the controller will then see an altitude relevant to that setting. Cant remember exactly how the computer assimilated the altitude of acft above this. I think that what you saw was always displayed relative to the QNH value entered just that above 3000, the altitude had a 0 put in front of it to show a FL?
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This covers it i think , more rasy than risy but you get the idea
"Under some circumstances, controllers may consider it prudent to inform a pilot of other traffic which is separated from his aircraft. In such cases, to prevent any possible confusion, no reference should be made to the actual level of the other aircraft. If necessary, the pilot should be informed that the other aircraft is '(number) thousand feet above/below'".
DTUP
"Under some circumstances, controllers may consider it prudent to inform a pilot of other traffic which is separated from his aircraft. In such cases, to prevent any possible confusion, no reference should be made to the actual level of the other aircraft. If necessary, the pilot should be informed that the other aircraft is '(number) thousand feet above/below'".
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On a point of pedantry. I believe the term "Regional QNH" is incorrect. As I understand it there is a "regional pressure setting" and a QNH.
The Regional Pressure Setting is a forecast of the lowest QNH value within an
altimeter setting region. The values which are made available hourly for the period H + 1 to H + 2, are given in whole millibars. MATS Pt1 Sec 1 Ch 6 Page 1.
I'd be interested to know if it is the QNH or the RPS that is being fed in to the Mil radar sets.
BurglersDog is not quite correct when he says that all aircrsft away from the circuit would be on RPS. No datum is specified (except when flying beneath a control are). I fly around on the local QNH whenever I can. Getting this from a military radar unit can be like pulling teeth though!
The "traffic 1000' above you" type of phraseology works well in controlled airspace where people tend to fly around at specified levels and there is scope for confusion. Outside controlled airspace I don't believe such confusion would be generated by actually reporting the level of the conflicting traffic eg. " traffic indicating 3200' unverified" etc.
I am all for standardisation, but I believe it can be taken too far so that the unexpected consequences outweigh the expected benefits. Giving the runway entry position at the same time as a line up instruction is another case in point. I now have to read back so much before I can get on to a runway that I hold all the information in my (very) short term memory. If you asked me 30s later what I had just read back I would struggle to remember. So whilst someone in an office thought they were making things safer by making me say "After the departing Midland A320 line up and wait runway 27L via N1" (even though the holding point between me and the runway is NB1), the key fact that I should line up after a Midland aeroplane is potentially lost as I try to resolve a bit of confusion as to where I should line up. There should be no confusion as there is only one way to get from where I am on to the runway, but still I am made slightly uncertain.
I rambled there a bit. The point I was trying to make is that we are starting to overcomplicate things. If you hear "Wembley-Hogg 001" on frequency, please just tell me what level the other traffic is at if I'm outside controlled airspace.
G W-H
The Regional Pressure Setting is a forecast of the lowest QNH value within an
altimeter setting region. The values which are made available hourly for the period H + 1 to H + 2, are given in whole millibars. MATS Pt1 Sec 1 Ch 6 Page 1.
I'd be interested to know if it is the QNH or the RPS that is being fed in to the Mil radar sets.
BurglersDog is not quite correct when he says that all aircrsft away from the circuit would be on RPS. No datum is specified (except when flying beneath a control are). I fly around on the local QNH whenever I can. Getting this from a military radar unit can be like pulling teeth though!
The "traffic 1000' above you" type of phraseology works well in controlled airspace where people tend to fly around at specified levels and there is scope for confusion. Outside controlled airspace I don't believe such confusion would be generated by actually reporting the level of the conflicting traffic eg. " traffic indicating 3200' unverified" etc.
I am all for standardisation, but I believe it can be taken too far so that the unexpected consequences outweigh the expected benefits. Giving the runway entry position at the same time as a line up instruction is another case in point. I now have to read back so much before I can get on to a runway that I hold all the information in my (very) short term memory. If you asked me 30s later what I had just read back I would struggle to remember. So whilst someone in an office thought they were making things safer by making me say "After the departing Midland A320 line up and wait runway 27L via N1" (even though the holding point between me and the runway is NB1), the key fact that I should line up after a Midland aeroplane is potentially lost as I try to resolve a bit of confusion as to where I should line up. There should be no confusion as there is only one way to get from where I am on to the runway, but still I am made slightly uncertain.
I rambled there a bit. The point I was trying to make is that we are starting to overcomplicate things. If you hear "Wembley-Hogg 001" on frequency, please just tell me what level the other traffic is at if I'm outside controlled airspace.
G W-H
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GWH Correct 
I was only generalising. RPS it is: Barnsley Holyhead etc
And of course being the lowest forecast for the period anyone flying on that instead of a local QNH will always be higher/ safer where terrain is concerned - but of course nearer to anyone overflying them, on the local QNH (or in the case of the mil within a MATZ- QFE), at what appears initially to be a safe alt above.
I cant remember what the mil or civs put into their radars,(1013 maybe as a standard ref) Im sure someone will soon tell. But I do know that when trying to coordinate arrivals and deps with LARS traffic, quick, accurate mental arithmatic was part and parcel of the daily tasks in order to work out whether you had the 500 or 1000' needed. Indeed as an RAF Instructor I often found that the pressure questions in an ATC groundschool phase were always a good test of the speed of a students processor so to speak. Often those that struggled to add or subtract correctly under a modicum of time pressure werent so good in the sim.
DogGone
I was only generalising. RPS it is: Barnsley Holyhead etc
And of course being the lowest forecast for the period anyone flying on that instead of a local QNH will always be higher/ safer where terrain is concerned - but of course nearer to anyone overflying them, on the local QNH (or in the case of the mil within a MATZ- QFE), at what appears initially to be a safe alt above.
I cant remember what the mil or civs put into their radars,(1013 maybe as a standard ref) Im sure someone will soon tell. But I do know that when trying to coordinate arrivals and deps with LARS traffic, quick, accurate mental arithmatic was part and parcel of the daily tasks in order to work out whether you had the 500 or 1000' needed. Indeed as an RAF Instructor I often found that the pressure questions in an ATC groundschool phase were always a good test of the speed of a students processor so to speak. Often those that struggled to add or subtract correctly under a modicum of time pressure werent so good in the sim.
DogGone
Last edited by BurglarsDog; 22nd Jun 2007 at 11:02.
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neilmac:
But that's just what you don't do - as riverboat said, what you actually do is read the Mode C of the other traffic, check against the Mode C of your own traffic, subtract one from the other, and give the result to the pilot of your traffic. Must be quite a lot of extra workload when busy, and lots of scope for error and confusion, not that I'd suggest ATCOs ever make errors
NS
we tell you what it is on our screens
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Transponder outputs altitude report in 100ft (or 25ft if Mode S and capable) based upon 1013.25 mB pressure. Setting QNH on altimeter, etc, will have no effect on the transponder. This will lead to transponder reported height being different to altimeter report based on QNH. Some of the more advanced radar processing and display systems will QNH convert the transponder altitude report when below transition altitude to give aircraft altitude in feet based on QNH rather than a Flight Level on 1013.25mB
What will be consistant is the difference in height between targets using the same 1013.23 mB pressure reference. So it is probably more correct to state differences in height of local traffic rather than their actual height AMSL that the radar display shows.
oh, and before someone makes a smartarse comment about transponder altitude reports being called Mode C, Mode S equipped aircraft (88%+ of all transponder equipped aircraft) do not use Mode C when responding in Mode S - hence I didn't call it Mode C.
I'll get off my Mode S soapbox now.........
What will be consistant is the difference in height between targets using the same 1013.23 mB pressure reference. So it is probably more correct to state differences in height of local traffic rather than their actual height AMSL that the radar display shows.
oh, and before someone makes a smartarse comment about transponder altitude reports being called Mode C, Mode S equipped aircraft (88%+ of all transponder equipped aircraft) do not use Mode C when responding in Mode S - hence I didn't call it Mode C.
I'll get off my Mode S soapbox now.........
Last edited by Radarspod; 22nd Jun 2007 at 11:20. Reason: small clarification ...
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As Radarspod points out, most radar display systems can be configured to convert the level reported by the transponder to another datum (instead of 1013.25 hPa). The setting chosen is going to be that which best suits the ATC operations. I'm an aerodrome person and all the radars I've ever worked have used the aerodrome QNH but if a unit provides a service that is not orientated around a particular aerodrome, a LARS for example (OK, a very UK example), it would probably make more sense to use the RPS because it is likely that many pilots will be using this setting.
Again, Radarspod pointed out that what we can be reasonably sure of is that the relative difference in reported altitudes is correct. As a controller providing services outside controlled airspace, I am going to be very aware of the differences in actual levels that may exist because of the different pressure settings used, quite legitimately, by different pilots. Where I give traffic information on another aircraft that I know is on a markedly different pressure setting I will probably give the level in relative terms - because, quite frankly, I can't be bothered to do the math. If I know the aircraft are using the same - or very close - data for altimeter setting I will probably give the level reported by the transponder. Bear in mind that the level information is likely to be unverrified anyway!
I would make one final observation. The pilot is flying according to the VFR - the information that the controller provides is intended to assist the pilot, not to replace looking out of the window, and is subject to workload and other factors. If a pilot wants more assurance of collision avoidance from the air traffic service there are more appropriate services to request.
Again, Radarspod pointed out that what we can be reasonably sure of is that the relative difference in reported altitudes is correct. As a controller providing services outside controlled airspace, I am going to be very aware of the differences in actual levels that may exist because of the different pressure settings used, quite legitimately, by different pilots. Where I give traffic information on another aircraft that I know is on a markedly different pressure setting I will probably give the level in relative terms - because, quite frankly, I can't be bothered to do the math. If I know the aircraft are using the same - or very close - data for altimeter setting I will probably give the level reported by the transponder. Bear in mind that the level information is likely to be unverrified anyway!
I would make one final observation. The pilot is flying according to the VFR - the information that the controller provides is intended to assist the pilot, not to replace looking out of the window, and is subject to workload and other factors. If a pilot wants more assurance of collision avoidance from the air traffic service there are more appropriate services to request.
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At the end of the day if I am providing a service to A/C they will be on my pressure setting, unless they are flying on 1013.2 .Therefore why have I got to worry about what pressure setting they are on .
Thats why I give the a/c my QNH.
If I am not working them, depending on the service I'm providing the maximum I have to do is , either seek to achieve 5nm or 3000' if I'm going for vertical.
If the squawk and charlie readout is validated and verified by an adjacent unit and co-ordination is acheived the slight difference between QNHs will hardly be noticed since the mode C readouts are to the nearest hundred.
Besides QNH is adjusted locally and A/c have A next to the level and Flight level has F next to it .
Where is the problem guys?
Thats why I give the a/c my QNH.
If I am not working them, depending on the service I'm providing the maximum I have to do is , either seek to achieve 5nm or 3000' if I'm going for vertical.
If the squawk and charlie readout is validated and verified by an adjacent unit and co-ordination is acheived the slight difference between QNHs will hardly be noticed since the mode C readouts are to the nearest hundred.
Besides QNH is adjusted locally and A/c have A next to the level and Flight level has F next to it .
Where is the problem guys?
Avoid imitations
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In my experience, ATC may say something along the lines of: "Traffic 11 o'clock, 3 miles, indicating 2400 feet unverified".
I take this to mean they are not in comms with the other aircraft and are merely reading off his Mode C indication. All encoding altimeters use 1013 as the datum so if necessary I might dial in 1013 mb on my second altimeter to check how his altitude compares to my own. Not difficult and is normally enough to help spot and ensure separation from him.
It is important to realise that his transponder may be giving a false readout; it would not have been confirmed in real time by the other pilot, due to the lack of ATC comms with him.
I also have the benefit of a TCAS; my readout should match the ATC report. However, as it also relies on his (the other pilot's) transponder being correct, it isn't completely infallible (in reality a transponder is only seldom very far out, it is checked at least annually, as part of the C of A airtest).
I take this to mean they are not in comms with the other aircraft and are merely reading off his Mode C indication. All encoding altimeters use 1013 as the datum so if necessary I might dial in 1013 mb on my second altimeter to check how his altitude compares to my own. Not difficult and is normally enough to help spot and ensure separation from him.
It is important to realise that his transponder may be giving a false readout; it would not have been confirmed in real time by the other pilot, due to the lack of ATC comms with him.
I also have the benefit of a TCAS; my readout should match the ATC report. However, as it also relies on his (the other pilot's) transponder being correct, it isn't completely infallible (in reality a transponder is only seldom very far out, it is checked at least annually, as part of the C of A airtest).
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Traffic 11 o'clock, 3 miles, indicating 2400 feet unverified
It is ambiguous, and short and choppy. I also emphasise the INDICATING and UNVERIFIED bit.
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I usually add "OH MY GOD HE'S HEADING STRAIGHT FOR YOU!!!!" and that tends to get someone's attention.
GWH, I agree with the new line-up phraseology. Hate it. One has to say it all very slowly to many operators to ensure they understand you, and it seems to go on forever!
GWH, I agree with the new line-up phraseology. Hate it. One has to say it all very slowly to many operators to ensure they understand you, and it seems to go on forever!
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""In my experience, ATC may say something along the lines of: "Traffic 11 o'clock, 3 miles, indicating 2400 feet unverified".I take this to mean they are not in comms with the other aircraft and are merely reading off his Mode C indication. All encoding altimeters use 1013 as the datum so if necessary I might dial in 1013 mb on my second altimeter to check how his altitude compares to my own. Not difficult and is normally enough to help spot and ensure separation from him.""
It is pointless to dial in 1013. Below the Transition Altitude the Mode C is automatically converted from that encoded on 1013 to altitude, verified or not. Remain on the controller's QNH. That is the setting fed into the radar.
It is pointless to dial in 1013. Below the Transition Altitude the Mode C is automatically converted from that encoded on 1013 to altitude, verified or not. Remain on the controller's QNH. That is the setting fed into the radar.
Avoid imitations
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Talkdownman,
Ah, point taken, but I might not be on the local QNH at all; I might be on RPS if it's a military radar unit. Local QNH at military airfields seems to be a military secret
I did say my second altimeter (co-pilot's side and I don't have a co-pilot). I obviously don't fly on 1013 if not at a flight level. I do sometimes need to have 1013 set on the other altimeter anyway, for example if climbing IFR to cruise in Class G under airspace which has a lower limit defined as a flight level.
Ah, point taken, but I might not be on the local QNH at all; I might be on RPS if it's a military radar unit. Local QNH at military airfields seems to be a military secret
I did say my second altimeter (co-pilot's side and I don't have a co-pilot). I obviously don't fly on 1013 if not at a flight level. I do sometimes need to have 1013 set on the other altimeter anyway, for example if climbing IFR to cruise in Class G under airspace which has a lower limit defined as a flight level.