Airbus FPA cold Weather
Thread Starter
Join Date: Nov 2019
Location: unknown
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
Airbus FPA cold Weather
I know it has been discussed before.
I was just reading an article about cold weather corrections in general and this statement was made...
"In 2015 there was a crash of an Airbus where the crew employed a company sanctioned procedure to increase their Flight Path Angle (FPA) to compensate for their increased Final Approach Fix altitude, which was temperature compensated. Flying the charted FPA from the higher indicated altitude at the FAF would result in arriving over the runway at too high an altitude. In theory, computing a higher FPA based on the expected indicated altitudes would get them over the threshold at the correct height. The problem with this theory is that the corrected FPA needs to be constantly updated. Airbus has since abandoned this procedure. If you've picked it up somewhere, you also need to abandon the procedure. Fly the charted FPA, even when using temperature compensated altitudes."
https://code7700.com/altimetry_tempe...ection.htm#fpa
I don't believe the writer is an Airbus pilot. Is this paragraph accurate, especially about the change of procedure and that no flight path angle change is made anymore?
I was just reading an article about cold weather corrections in general and this statement was made...
"In 2015 there was a crash of an Airbus where the crew employed a company sanctioned procedure to increase their Flight Path Angle (FPA) to compensate for their increased Final Approach Fix altitude, which was temperature compensated. Flying the charted FPA from the higher indicated altitude at the FAF would result in arriving over the runway at too high an altitude. In theory, computing a higher FPA based on the expected indicated altitudes would get them over the threshold at the correct height. The problem with this theory is that the corrected FPA needs to be constantly updated. Airbus has since abandoned this procedure. If you've picked it up somewhere, you also need to abandon the procedure. Fly the charted FPA, even when using temperature compensated altitudes."
https://code7700.com/altimetry_tempe...ection.htm#fpa
I don't believe the writer is an Airbus pilot. Is this paragraph accurate, especially about the change of procedure and that no flight path angle change is made anymore?
I know it has been discussed before.
I was just reading an article about cold weather corrections in general and this statement was made...
"In 2015 there was a crash of an Airbus where the crew employed a company sanctioned procedure to increase their Flight Path Angle (FPA) to compensate for their increased Final Approach Fix altitude, which was temperature compensated. Flying the charted FPA from the higher indicated altitude at the FAF would result in arriving over the runway at too high an altitude. In theory, computing a higher FPA based on the expected indicated altitudes would get them over the threshold at the correct height. The problem with this theory is that the corrected FPA needs to be constantly updated. Airbus has since abandoned this procedure. If you've picked it up somewhere, you also need to abandon the procedure. Fly the charted FPA, even when using temperature compensated altitudes."
https://code7700.com/altimetry_tempe...ection.htm#fpa
I don't believe the writer is an Airbus pilot. Is this paragraph accurate, especially about the change of procedure and that no flight path angle change is made anymore?
I was just reading an article about cold weather corrections in general and this statement was made...
"In 2015 there was a crash of an Airbus where the crew employed a company sanctioned procedure to increase their Flight Path Angle (FPA) to compensate for their increased Final Approach Fix altitude, which was temperature compensated. Flying the charted FPA from the higher indicated altitude at the FAF would result in arriving over the runway at too high an altitude. In theory, computing a higher FPA based on the expected indicated altitudes would get them over the threshold at the correct height. The problem with this theory is that the corrected FPA needs to be constantly updated. Airbus has since abandoned this procedure. If you've picked it up somewhere, you also need to abandon the procedure. Fly the charted FPA, even when using temperature compensated altitudes."
https://code7700.com/altimetry_tempe...ection.htm#fpa
I don't believe the writer is an Airbus pilot. Is this paragraph accurate, especially about the change of procedure and that no flight path angle change is made anymore?
That author is wrong.
From the current A319 FCOM:
I actually shot an RNAV approach in FPA at sea level at -27°C just 5 days ago. If I'd used the charted FPA (-2.54°) I'd have missed for sure.
I don't use the following in anger because of the variables but I got bored one day many moons ago and worked it out theoretically (cut and paste from my old notes):
•H = FAFcorr – MINIMAcorr (in feet)
•D=(Distance FAF to MINIMA )nm * 6072 (turns miles into feet)
•On your iPhone calculator – turn sideways for scientific….
a)Find H/D
b)Press tanh gives angle in radians
c)*180/pi
This is the Actual FPA that needs to be dialled into the FCU
From the current A319 FCOM:
When the temperate is lower than ISA:
‐ The true altitude of the aircraft is lower than the altitude that the ADIRS computes.
‐ The FPA that the aircraft actually flies, is less steep than the FPA that the ADIRS computes.
If appropriate, the flight crew should therefore apply corrections on the altitudes and on the FPA (in vertical selected FPA mode), and they should be vigilant on the parameters that are displayed.
....
FPA Correction
When the temperature is lower than ISA, the FPA that the aircraft actually flies is less steep than the FPA that the ADIRS (ISA referenced) computes. In vertical selected mode FPA, to correct the FPA for this ISA deviation effect, the flight crew should select on the FCU a FPA slightly different from the FPA that the aircraft needs to fly.
In any case, the check "altitude (corrected in temperature) versus distance" remains the reference.
‐ The true altitude of the aircraft is lower than the altitude that the ADIRS computes.
‐ The FPA that the aircraft actually flies, is less steep than the FPA that the ADIRS computes.
If appropriate, the flight crew should therefore apply corrections on the altitudes and on the FPA (in vertical selected FPA mode), and they should be vigilant on the parameters that are displayed.
....
FPA Correction
When the temperature is lower than ISA, the FPA that the aircraft actually flies is less steep than the FPA that the ADIRS (ISA referenced) computes. In vertical selected mode FPA, to correct the FPA for this ISA deviation effect, the flight crew should select on the FCU a FPA slightly different from the FPA that the aircraft needs to fly.
In any case, the check "altitude (corrected in temperature) versus distance" remains the reference.
I don't use the following in anger because of the variables but I got bored one day many moons ago and worked it out theoretically (cut and paste from my old notes):
•H = FAFcorr – MINIMAcorr (in feet)
•D=(Distance FAF to MINIMA )nm * 6072 (turns miles into feet)
•On your iPhone calculator – turn sideways for scientific….
a)Find H/D
b)Press tanh gives angle in radians
c)*180/pi
This is the Actual FPA that needs to be dialled into the FCU
Last edited by compressor stall; 18th Mar 2020 at 09:39.
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,407
Likes: 0
Received 0 Likes
on
0 Posts
The article appears to be from aviation journalist and is vague. In any NPA using barometric altitude the correction will have to be applied. Airbus having FLS uses automatic correction and aircraft capable of GLS or SLS use geometric altitude so the correction is not applicable. However these approaches are performed ILS like with FDs and presently are not available in Airbus narrow bodies or A330.
Join Date: Jun 2004
Location: Just Around The Corner
Posts: 1,395
Likes: 0
Received 0 Likes
on
0 Posts
tcasblue and Vilas - it appears his mistake is to assume that the aircraft gemoetrically descends at the increased FPA. He analysed the AC624 crash here https://code7700.com/altimetry_tempe...ection.htm#fpa
Half way down he states that the aircraft descends geometrically at the increased FPA from the uncorrected altitude, ending up low.
In any case, TC states that the aircraft ended up low due to momentary windshears and does not correct (which it won't). The crew then did not monitor the profile as per the FCOM. The requirement to refine the FPA during the descent has nothing to do with the cold (assuming a uniform temperature gradient and level ground under the approach)
Half way down he states that the aircraft descends geometrically at the increased FPA from the uncorrected altitude, ending up low.
In any case, TC states that the aircraft ended up low due to momentary windshears and does not correct (which it won't). The crew then did not monitor the profile as per the FCOM. The requirement to refine the FPA during the descent has nothing to do with the cold (assuming a uniform temperature gradient and level ground under the approach)
Last edited by compressor stall; 18th Mar 2020 at 11:19.
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,407
Likes: 0
Received 0 Likes
on
0 Posts
The real problem was their SOP wrongly asked the crew not carry out Distance/ altitude checks. What the article meant by corrected FPA needs to be continuously updated was height needs to be checked Vs Dist and adjusted as required which is done even at normal temperature. But the conclusion is opposite and wrong. They had also sued Airbus on this. What came out of it I don't know.
Thread Starter
Join Date: Nov 2019
Location: unknown
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
This is not in my QRH(320 series). I see the date on your page is a 2012 issue date. The accident happened in 2015. What is the date of your QRH publication?
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,407
Likes: 0
Received 0 Likes
on
0 Posts
tcasblue
First low temperature correction has to be applied to final descent altitude and the minimum. To track this corrected vertical profile you use corrected FPA. The responsibility to ensure you are tracking correct vertical path is with crew by normal DME/altitude (corrected) checks.
First low temperature correction has to be applied to final descent altitude and the minimum. To track this corrected vertical profile you use corrected FPA. The responsibility to ensure you are tracking correct vertical path is with crew by normal DME/altitude (corrected) checks.
Thread Starter
Join Date: Nov 2019
Location: unknown
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
tcasblue
First low temperature correction has to be applied to final descent altitude and the minimum. To track this corrected vertical profile you use corrected FPA. The responsibility to ensure you are tracking correct vertical path is with crew by normal DME/altitude (corrected) checks.
First low temperature correction has to be applied to final descent altitude and the minimum. To track this corrected vertical profile you use corrected FPA. The responsibility to ensure you are tracking correct vertical path is with crew by normal DME/altitude (corrected) checks.
Reading the report here...
https://www.tsb.gc.ca/eng/rapports-r.../a15h0002.html
The published descent angle was almost 3.1 degrees with a temperature of -5C. Yet they chose to use an FPA of 3.5 which the report says was in agreement with the company procedures(which were different than Airbus procedures). But it seems like the chart published on this thread(which is not in my QRH) shows that one might use 3.2 degrees. I this correct.
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,407
Likes: 0
Received 0 Likes
on
0 Posts
tcasblue
The following faulty procedure of Air Canada was an accident waiting to happen:
The following faulty procedure of Air Canada was an accident waiting to happen:
Air Canada's practice was that, once the aircraft was past the FAF, the flight crews were not required to monitor the aircraft's altitude and distance from the threshold, nor to make any adjustments to the FPA.
Join Date: Jul 2006
Location: Somewhere over the rainbow
Posts: 946
Likes: 0
Received 0 Likes
on
0 Posts
I'm a bit confused. I understand that on cold weather the real aircraft altitude is lower than the indicated one. I never knew that the FPA that the aircraft actually flies, is less steep than the FPA that the ADIRS computes. How is that possible? I would think the opposite to be true.
FPA is calculated from Baro inputs. When showing 2200 (and it’s actually at 2000) it “thinks” it’s higher then it is. Ergo it needs a higher descent angle to compensate to the threshold where the correction is zero.
Remember the correction amount is relative to height over ground. The correction at 2000’ is twice that at 1000’ etc. Rather than the complex formula and apps, just use 4•ISAD•height over ground/1000.
Remember the correction amount is relative to height over ground. The correction at 2000’ is twice that at 1000’ etc. Rather than the complex formula and apps, just use 4•ISAD•height over ground/1000.
Join Date: Jul 2006
Location: Somewhere over the rainbow
Posts: 946
Likes: 0
Received 0 Likes
on
0 Posts
Sorry Compressor stall, I still don't understand. Could you give an example using your formula?
You quote from the FCOM:
The way I understand: when it's colder than ISA: If you select FPA-3.0, and it's minus 30 degrees outside, the actual FPA flown by the plane will be lower than 3.0 degrees, so according to the correction table above, the crew needs to set FPA -3.3 degrees on the FCU. Am I correc?
That's why I don't understand when you say: It ''thinks'' it's higher then it is.
Thank you.
You quote from the FCOM:
When the temperate is lower than ISA:
‐ The true altitude of the aircraft is lower than the altitude that the ADIRS computes.
‐ The FPA that the aircraft actually flies, is less steep than the FPA that the ADIRS computes
‐ The true altitude of the aircraft is lower than the altitude that the ADIRS computes.
‐ The FPA that the aircraft actually flies, is less steep than the FPA that the ADIRS computes
That's why I don't understand when you say: It ''thinks'' it's higher then it is.
Thank you.
Essentially yes I think your summary is correct. Re it "thinking" it is higher that it is - let me explain my logic and terminology.
Assume:
If you did no temp correction, the aircraft would fly at 2000 on the FCU, but be actually around 1720' on the RADALT. (The 1720 is calculated by 2000-(4*35*2)). If you set -3° on the FPA, the aircraft "thinks" it's at 2000' (its getting baro info, not RADALT or geometric info) and would fly a profile to the threshold quite successfully (assuming it didn't hit anything on the way
). It, however, has not flown a geometric 3 degree slope, rather it has flown a slope of 1720' over 6.3*6072' which is about 2.57° geometric.
If you temp correct:
That said, I think the figures in the table above are slightly conservative. I don't know why (nor why they are not in the A320 FCOM) The manuals seem to be updated in late 2017 for the A32F and interestingly not in the Main FCOM/FCTM changes documents from that period that I can find.
Assume:
- Sea level airport
- METAR calling -20°C at the runway
- That's ISA-35
- Uniform atmosphere, and approach overwater.
- NPA FAF@ 2000' at 6.3nm from threshold (3°slope).
- Minima 250 (ignoring PEC) 0.8nm from threshold (I know there's another 50' over the threshold but it doesn't really matter here)
If you did no temp correction, the aircraft would fly at 2000 on the FCU, but be actually around 1720' on the RADALT. (The 1720 is calculated by 2000-(4*35*2)). If you set -3° on the FPA, the aircraft "thinks" it's at 2000' (its getting baro info, not RADALT or geometric info) and would fly a profile to the threshold quite successfully (assuming it didn't hit anything on the way
). It, however, has not flown a geometric 3 degree slope, rather it has flown a slope of 1720' over 6.3*6072' which is about 2.57° geometric.If you temp correct:
- For the FAF: to have the RADALT at 2000' you'd need to set 2000+(4*35*2)=2280' on the FCU. Call this FAFcorr. The cold weather correction is 280' at the FAF
- For the minima: to have the RADALT at 250' you'd need to be at 250+(4*35*.25) = 285. Call this MINcorr The cold weather correction at the minima is 35' (the correction is less the closer to the ground).
That said, I think the figures in the table above are slightly conservative. I don't know why (nor why they are not in the A320 FCOM) The manuals seem to be updated in late 2017 for the A32F and interestingly not in the Main FCOM/FCTM changes documents from that period that I can find.
Last edited by compressor stall; 19th Mar 2020 at 11:33.
The published descent angle was almost 3.1 degrees with a temperature of -5C. Yet they chose to use an FPA of 3.5 which the report says was in agreement with the company procedures(which were different than Airbus procedures). But it seems like the chart published on this thread(which is not in my QRH) shows that one might use 3.2 degrees. I this correct.
Thread Starter
Join Date: Nov 2019
Location: unknown
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
Almost. Because the chart’s based on ISA deviation rather than raw temperature, you’re looking at around ISA-20C (actually -19 for the elevation there, but near enough), so 3.1 degrees becomes 3.3. The airfield temperature would have to have been -25C (ISA-40) for 3.5 degrees to be correct.
I wonder if the 0.2 degree difference between this chart and what was actually used correspond with the flight path error.
The report seems to be careful to say that the correction they made was in accordance with company procedures(which were different from Airbus procedures but approved by the regulator) but they do not say if these procedures were accurate.
Thread Starter
Join Date: Nov 2019
Location: unknown
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
A lot of interesting information(although they only seem to mention for A350 and A300) but nothing about adjusting FPA descent angle. Apparently, my company is not the only narrowbody Airbus operator without the FPA adjustment chart that was posted earlier from an A330 QRH.