Adjusting the ILS minima
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Altimeter Check
Very Dangerous quoting old AIP reference. The current date for ENR 1.5 - 32 para 7 is 27 AUG 09
Currently if there is an unexplained discrepancy at the check point then an immediate go around is called for.
So if temperature has been taken into account and all is as calculated then continue.
And remember a correction calculation must be made for every check height,
GS intercept-OM/DME check and minima.
Currently if there is an unexplained discrepancy at the check point then an immediate go around is called for.
So if temperature has been taken into account and all is as calculated then continue.
And remember a correction calculation must be made for every check height,
GS intercept-OM/DME check and minima.
sleeve of wizard
I’m not sure what you are getting at? If you are in the terminal area you should be on QNH, not standard. If, as I think you are alluding to, you should correct the “Minimum Route Altitude” for high wind speeds which can cause the barometric altimeters to over read because of a possible non-standard atmospheric pressure, i.e. on the lee side of the mountains, then I agree with you. Most airlines should have correction tables for this in their ops manual.
If though you are suggesting while being radar vectored in a TMA, ie MVA that you need to make a correction simply because the QNH is different to standard then I don’t agree. If you are descending to an MRA after say a depress then you would be descending on an area QNH, not standard. Wind correction would be required if in my companies case the winds are greater than 30 kts at MRA.
I’m not sure what you are getting at? If you are in the terminal area you should be on QNH, not standard. If, as I think you are alluding to, you should correct the “Minimum Route Altitude” for high wind speeds which can cause the barometric altimeters to over read because of a possible non-standard atmospheric pressure, i.e. on the lee side of the mountains, then I agree with you. Most airlines should have correction tables for this in their ops manual.
If though you are suggesting while being radar vectored in a TMA, ie MVA that you need to make a correction simply because the QNH is different to standard then I don’t agree. If you are descending to an MRA after say a depress then you would be descending on an area QNH, not standard. Wind correction would be required if in my companies case the winds are greater than 30 kts at MRA.
as this is the GA section i can only assume the original question was regarding the good old "trying to trip you up" questions used by interviewers and on renewals.
as i understand it, if there is an unexplained discrepancy you have two options.
1. continue with the LLZ app
2. conduct a missed app.
and FRQ CB as to your question ie if your below LLZ minima you only have one choice, missed app!
as i understand it, if there is an unexplained discrepancy you have two options.
1. continue with the LLZ app
2. conduct a missed app.
and FRQ CB as to your question ie if your below LLZ minima you only have one choice, missed app!
The subject has been discussed numerous times in the past as this thread from the year 2000 shows
http://www.pprune.org/tech-log/10870...r-checked.html
The Flight Safety Foundation also have a publication related to this
http://flightsafety.org/files/alar_bn3-1-altimeter.pdf
Altitude/Temperature correction charts show only a small correction if the temperature is above -20C and the airfield below 700' elevation. -30C and 5000' gives an 820' error
Barometric altimeters and manual flying obviously have their limitations, hence Rad Alt and autopilot for CAT 3.
Some airlines won't allow this below a certain altitude as there isn't sufficient time to adjust, a go around is mandatory
http://www.pprune.org/tech-log/10870...r-checked.html
The Flight Safety Foundation also have a publication related to this
http://flightsafety.org/files/alar_bn3-1-altimeter.pdf
Altitude/Temperature correction charts show only a small correction if the temperature is above -20C and the airfield below 700' elevation. -30C and 5000' gives an 820' error
Barometric altimeters and manual flying obviously have their limitations, hence Rad Alt and autopilot for CAT 3.
as i understand it, if there is an unexplained discrepancy you have two options.
1. continue with the LLZ app
1. continue with the LLZ app
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Digging up this old thread after a considerable amount of research (PPRuNe, AIP, textbooks, YouTube etc) I thought I should point out a new link to an old video about NZ60 into Faleolo.
This video, whilst not exactly about Temp corrections, is about altitude cross checking and for that reason is entirely relevant to the topic at hand (i.e. an "unexplained discrepancy").
FRQ CB
PS For some reason this video keep getting deleted despite the fact that it shows ANZ in a good light... maybe because people keep editing it and make the airline look bad. Not much of an issue now that YouTube don't have the old 10.5 minute limit.
This video, whilst not exactly about Temp corrections, is about altitude cross checking and for that reason is entirely relevant to the topic at hand (i.e. an "unexplained discrepancy").
FRQ CB
PS For some reason this video keep getting deleted despite the fact that it shows ANZ in a good light... maybe because people keep editing it and make the airline look bad. Not much of an issue now that YouTube don't have the old 10.5 minute limit.
Great training video!
I wonder if there would have been a very different outcome if they were in IMC to the minimas (ie. not seeing the lights - trigger mechanism).
** Note Armchair expert hat on.
I wonder if there would have been a very different outcome if they were in IMC to the minimas (ie. not seeing the lights - trigger mechanism).
** Note Armchair expert hat on.
Last edited by havick; 19th Apr 2012 at 10:35.
as i understand it, if there is an unexplained discrepancy you have two options.
1. continue with the LLZ app
2. conduct a missed app.
1. continue with the LLZ app
2. conduct a missed app.
Think about the reason behind the rule. If you have an unexplained error at the check altitude (so we are not talking about temperature corrections) then you MUST suspect your altimeter is mis-set (or has a large error). You thus would be pretty stupid to continue to descend IFR to ANY minima (such as a LLZ minima) knowing that your altimeter is mis-set.
The AIP rule is there to get you to go-around, identify and fix the problem (confirm the QNH, inquire as to the serviceability of the Glide Slope, inquire as to whether an aircraft was taxiing past - ie. it wasn't protected, cross-check altimeter/static sources etc etc) - and once it is fixed, you may attempt another approach (of whatever type).
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Regarding temperature corrections.
You can get used to the topic, by always considering "hot day or cold day?" when flying an ILS. Get used to the altimeter under- or over-reading and you'll develop a feel for what looks right on any given day. This will help greatly when one day you have a 50' error at the FAP because it's 40 degrees at sea level.
On another note. Why do Australian pilots like to check height only at a marker beacon, notwithstanding Ancient's advice? DME (or GPS in lieu of DME) is both more accurate and more flexible.
You can get used to the topic, by always considering "hot day or cold day?" when flying an ILS. Get used to the altimeter under- or over-reading and you'll develop a feel for what looks right on any given day. This will help greatly when one day you have a 50' error at the FAP because it's 40 degrees at sea level.
On another note. Why do Australian pilots like to check height only at a marker beacon, notwithstanding Ancient's advice? DME (or GPS in lieu of DME) is both more accurate and more flexible.
