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Temperature correction on Baro-VNAV approach
Hello everybody,
I know Baro-VNAV approaches have been discussed on PPRuNe before, but I haven't been able to find a definitive answer to my question. Even after reading the FCOM as well as any relevant reference material available in my company, I'm still not sure what I'm really supposed to do. Let me give you the following situation: RNP APCH with VNAV minima OAT -10 degr. Note on plate: uncompensated Baro-VNAV not authorised below -20 degr. "RNP APCH APV procedures are designed with a linear obstacle profile from the FAF to the DA. This obstacle clearance is assured down to the minimum temperature as mentioned in the minima box in the ‘notes’ section. This means that no temperature corrections in the final approach segment are necessary if the OAT is higher than the value mentioned in the note. Note that for temperatures below zero, corrections to MDA and DA should be applied for both types of approaches." The information sounds quite contradictory to me. Yes, the temperature is below zero ("corrections to DA should be applied"), and yes, the OAT is higher than the value mentioned in the note ("no temperature corrections in the final approach segment (which includes the DA) are necessary"). So, should I correct the DA or not? Thanks! |
There are two different questions. 1) Do I need to correct my DA/MDA 2) Am I allowed to follow the vertical path and related LNAV/VNAV minima.
To answer question 1. --> Every time the temperature drops below 0, the DA/MDA needs to be corrected. My company uses 10% of the height, to be added to the DA/MDA. So if the minima is 400'(300), where the height is in brackets, the new minima becomes 400' plus 10% of 300' --> 430'*. The second question depends on the equipment that you have on board. On some airplanes you'll have temperature compensated systems, like FLS on some Airbuses. If you do NOT have temperature compensated equipment, you can only follow the vertical path until the published temperature on the chart, or 0ºC. In your example the published temperature is -20º, so you're authorized to follow the vertical guidance down to LNAV/VNAV minima (but these need to be corrected, see question 1). |
The information sounds quite contradictory to me. Yes, the temperature is below zero ("corrections to DA should be applied"), and yes, the OAT is higher than the value mentioned in the note ("no temperature corrections in the final approach segment (which includes the DA) are necessary"). So, should I correct the DA or not? |
For a new student, it might be a logical interpretation. "The profile takes you from FAF to 50' over the threshold (by definition) and indeed the DA is somewhere on it. With cold airmass, the whole slope gets flattened: yet there is no need to make corrections as the profile has been smartly designed to cater for this effect down to -20 deg.C - NICE. At the same time, the DA needs to be manually adjusted at -0 already ?! WTF...."
Dutch: - the (M)DA is the minimum and we are not allowed to go lower than that, geometrically. Hence the correction. - the profile is just the slope from FAF to THR. You are safe as the flattening had been taken care of, as long as you observe geometrical the (M)DA. |
Thank you for your suggestions. It sounds really natural to correct the DA since you don't want to go below the actual published minimum altitude, so I see what you guys are doing. However, in my company's latest documentation (August 2018) I can read the following statement: "As per EASA regulation temperature corrections for the FAF and DA are no longer allowed when flying RNP approaches down to VNAV minima." Could this mean that the published FAF and DA are determined using the minimum temperature for the procedure. Then no correction would be necessary, even if you're below zero (but not exceeding -20 in this case). For the second question, we operate the 737 so it's uncompensated Baro-VNAV. Means we can fly the approach down to the minimum temperature, like you said. Thanks again! |
Re read your SP 16. n altitude correction due to cold temperature is not needed for the following conditions: • while under ATC radar vectors • when maintaining an ATC assigned flight level (FL) • when the reported airport temperature is above 0°C or if the airport temperature is at or above the minimum published temperature for the procedure being flown. |
Dutchman95, it could be though unlikely unless you have some very customised approach plates? However, I would really like to read the two lines before and after the above quote.
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AMC2 CAT.OP.MPA.126
(i) For RNP APCH operations to LNAV/VNAV minima using Baro VNAV: (A) the flight crew should not commence the approach when the aerodrome temperature is outside the promulgated aerodrome temperature limits for the procedure unless the area navigation system is equipped with approved temperature compensation for the final approach; (B) when the temperature is within promulgated limits, the flight crew should not make compensation to the altitude at the FAF and DA/H; (C) since only the final approach segment is protected by the promulgated aerodrome temperature limits, the flight crew should consider the effect of temperature on terrain and obstacle clearance in other phases of flight. |
Thanks FlyingStone for the reference. Despite that, my company just started with cold temp corrections to all published altitudes below corrected MSA on baro-VNAV.. Apparently there were two different schools, and someone's ego stronger than the others. :zzz: |
172 driver, Do you have an fcom?�� |
Originally Posted by de facto
(Post 10296476)
172 driver, Do you have an fcom?�� I found it strange that Boeing would publish something like that. Though most, not all ATC units correct for low temperature. Oslo TMA for instance. |
I believe the confusion is between the applicable correction and the DA(DH) that pilots do actually "bug" on the PFD. No corrections are applicable between the FAF and DA(DH) but Your company procedures may require You to "bug" a temperature corrected DA which has obviously zero effect on the profile.
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Actually, this is a big discussion in our airline as well(another Dutch company). The initilal guidance in our manual when we first started flying RNP approaches was that you did have to correct the DA for low temperatures, even though you were within the temp bracket to fly to LNAV/VNAV minima. I did some research and have found several documents backing this up. However, as a previous poster already posted, since 2016, EASA guidance states that when above the minimum temperature stated on the approach chart, temperature corrections are not to be made to the DA, even though the temperature is below 0!! |
Originally Posted by flyburg
(Post 10296651)
Actually, this is a big discussion in our airline as well(another Dutch company). The initilal guidance in our manual when we first started flying RNP approaches was that you did have to correct the DA for low temperatures, even though you were within the temp bracket to fly to LNAV/VNAV minima. I did some research and have found several documents backing this up. However, as a previous poster already posted, since 2016, EASA guidance states that when above the minimum temperature stated on the approach chart, temperature corrections are not to be made to the DA, even though the temperature is below 0!!
Originally Posted by sonicbum
(Post 10296582)
I believe the confusion is between the applicable correction and the DA(DH) that pilots do actually "bug" on the PFD. No corrections are applicable between the FAF and DA(DH) but Your company procedures may require You to "bug" a temperature corrected DA which has obviously zero effect on the profile.
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172driver.... Your lack of basic knowledge is frightening. |
172driver.... Your lack of basic knowledge is frightening. Cmon then keyboard warrior... explain what I am lacking: So far I've stated; 1. Our company applies cold temp corrections on baro-VNAV, as of recently, to all altitudes below temp corrected MSA. That includes, step-down altitudes, FAF, DA - despite what the FCOM Supp. Proc. says and the reference to AMC.CAT.OP.MPA. It ain't dangerous, we're just flying slightly steeper than we would have otherwise done in say - 20 deg. 2. Regardless what the Supp Proc.says, there are ATC units that do not apply cold temp corrections to vector altitudes. We have it in our network. So for Boeing to generalize in such manner, I found rather puzzling. I thought the lawyers what have looked it through? |
Dutchman, What does the chart say? Does it say "uncompensated baro-vnav"?
When we design the procedure, there is the NA above and below temperatures. If you are between the NA above and NA below, the OCS has been validated to avoid the obstacles, from IF onwards. In FAA land, the NA below takes you to a 2.75 degree glidepath (ICAO goes to a 2.5 GPA) The NA above takes to you a 3.5 GPA. So uncompensated, you are between basically 2.5 and 3.5 degrees and the OCS has been validated for this. Therefore, if you are within the temperature boundary, you do not need to correct the FAF nor the DA/MDA altitudes. Again, if the chart states uncompensated baro vnav, which I think they all do, or it is assumed uncomp. IF you get outside the temperature limits, you must either not use the procedure or correct... Bottom line, when you use the procedure, you do not have to compensate if you are within the temperature boundaries. IF your system has the ability to compensate, all the better, but not req'd. The FMS, not the driver outside of the FMS. Keep in mind, if you simply add a factor to the altitude, say the FAF or DA, while your system remains uncompensated, that is a problem. This is why many ATC vectors will not allow for compensation, due to the blend of ac with the system ability or not, and not to rely on the drivers to be consistent in the correction . Our company applies cold temp corrections on baro-VNAV, as of recently, to all altitudes below temp corrected MSA. That includes, step-down altitudes, FAF, DA - despite what the FCOM Supp. Proc. says and the reference to AMC.CAT.OP.MPA. If your FCOM says no, I am not sure what the question is here. I would be curious what your SOP then uses as the temperature limit before you decide to correct? You with AC? |
My understanding, and the procedure at a major UK operator with a large fleet of uncompensated B737s, is that you would fly the approach to LNAV/VNAV minima without any corrections provided the temperature was within the charted limit. If the temperature drops below the charted limit you can still fly the approach, but to LNAV minima only and with temperature corrections applied.
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Originally Posted by Dutchman95
(Post 10296959)
We don't do that, our manual clearly states "the uncorrected DA is set on the PFD". Using a corrected DA on the flatter vertical path would also increase the required distance to make visual contact with the runway.
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It does not affect the profile, but should you raise the DA to the original geometric value, on a flatter profile the point where slope-x-DA would be further from the runway. That, in turn, should (?) force you to recalculate the minimum RVR / OPS 1.430. Shyte what a can of worms.
Originally Posted by underfire
Therefore, if you are within the temperature boundary, you do not need to correct the FAF nor the DA/MDA altitudes.
I trust you the slope covers me over OCA/H until the LO temp limit and that you guys did your math well. The OPS side has, in addition, some minima as well. Such as the DA is never less than 250 ft on RNP-baroVNAV. That's where the old method was more readily understandable. Anyways Dutchman95 thanks for coming here, I learned something through your question. |
Originally Posted by underfire
(Post 10297208)
Dutchman, What does the chart say? Does it say "uncompensated baro-vnav"?
When we design the procedure, there is the NA above and below temperatures. If you are between the NA above and NA below, the OCS has been validated to avoid the obstacles, from IF onwards. In FAA land, the NA below takes you to a 2.75 degree glidepath (ICAO goes to a 2.5 GPA) The NA above takes to you a 3.5 GPA. So uncompensated, you are between basically 2.5 and 3.5 degrees and the OCS has been validated for this. Therefore, if you are within the temperature boundary, you do not need to correct the FAF nor the DA/MDA altitudes. Again, if the chart states uncompensated baro vnav, which I think they all do, or it is assumed uncomp. IF you get outside the temperature limits, you must either not use the procedure or correct... Bottom line, when you use the procedure, you do not have to compensate if you are within the temperature boundaries. IF your system has the ability to compensate, all the better, but not req'd. The FMS, not the driver outside of the FMS. Keep in mind, if you simply add a factor to the altitude, say the FAF or DA, while your system remains uncompensated, that is a problem. This is why many ATC vectors will not allow for compensation, due to the blend of ac with the system ability or not, and not to rely on the drivers to be consistent in the correction . With regard to your last remark, we don't correct while receiving radar vectors, unless (!) one of the minimum altitudes in the procedure is below the minimum vectoring altitude (MVA). Without checking I'm not entirely sure if this is stated in the FCOM or just company policy though. @FlightDetent That's exactly the reason why I believe adjusting the DA on a Baro-VNAV approach doesn't make sense in the first place, because of this increased distance to the threshold. But yeah, it's good for getting a better understanding of what we're actually doing, so cheers for thinking along with me! |
Whats all this nonsense? You should absolutely temperature correct your M(DA). The chart has been designed, as others have stated, to keep you clear of obstacles withinin the temperaure range. The chart designer choses a min temp based on historical min temps at the airport and uses It if he can (ie if the GP is not too shallow (min 2.5deg icao) and obstacles do not penetrate the obstacle clearance screen). If these conditions cannot br met then either the GP is steepened (increase FAF alt), the minimum temp is increased or both. the M(DA) has nothing to do with this. The designer could in theory also correct the M(DA) for us By selecting the most conservative M(DA), ie one that will allow us to be at the minimum geometric altitude at the lowest temp. This however will be overly restrictive for most of the year when the temperature is above that value. This is why we must amend the M(DA) |
Listen to Matey:p |
Originally Posted by de facto
(Post 10298629)
Listen to Matey:p |
Stop with the insults and give us something useful, de facto. |
Originally Posted by InSoMnIaC
(Post 10298441)
Whats all this nonsense? You should absolutely temperature correct your M(DA). For RNP APCH operations to LNAV/VNAV minima using Baro VNAV:
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In addition, AMC stands for Acceptable Means of Compliance, and under EASA that actually is the only approved means of compliance. If you want to do different, you need to apply for an alternative means with EASA themselves (local national CAA won't do). Unlike in the days of EU-OPS / JAA.
Applies for all EU registered aircraft. Presumably, they did the homework rather well, and it is the right thing. Until this thread, my understanding was the same as InSoMnIaC's. |
Originally Posted by FlightDetent
(Post 10298830)
...
under EASA that actually is the only approved means of compliance. If you want to do different, you need to apply for an alternative means with EASA themselves (local national CAA won't do). Unlike in the days of EU-OPS / JAA. ... . EASA maintains a list of notified AltMoCs, which are available for use by other organidsations with the agreement of their competent authority. |
:ooh: Sepp is perfectly correct: ARO.GEN.150.
Now that the book is opened - the relation between the approach angle, (M)DA and min RVR is explained in AMC5 CAT.OP.MPA.110. (Not that I really understand how to apply it, luckily not my job.) |
It is my understanding that you can fly it within the temperature limit stated on the chart, BUT the DA or MDA should be corrected because it is not taken in account when constructing the path, in fact you can use different minima depending on the onboard equipment and certification, the path flown will be the same whatever minima you use, and will be flatter if cold or steeper if warm, but the minima should be temperature corrected.
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I have had this discussion with my current UK airline too.
We currently correct everything below the temp corrected MSA, for all approaches. In my previous airline, we did not correct anything between and including the FAF - DA on a Baro-VNAV approach. I showed the AMC to the company who replied that they were within their right to be more conservative and correct anyway - I disagreed as it explicitly states that we should not do it - but was over-ruled. I still disagree - but nonetheless, I suppose this shows how straight forward and unified this all is. |
t is my understanding that you can fly it within the temperature limit stated on the chart, BUT the DA or MDA should be corrected because it is not taken in account when constructing the path, in fact you can use different minima depending on the onboard equipment and certification, the path flown will be the same whatever minima you use, and will be flatter if cold or steeper if warm, but the minima should be temperature corrected. Again... When we design the procedure, there is the NA above and below temperatures. If you are between the NA above and NA below, the OCS has been validated to avoid the obstacles, from IF onwards. In FAA land, the NA below takes you to a 2.75 degree glidepath (ICAO goes to a 2.5 GPA) The NA above takes to you a 3.5 GPA. So uncompensated, you are between basically 2.5 and 3.5 degrees and the OCS has been validated for this. Therefore, if you are within the temperature boundary, you do not need to correct the FAF nor the DA/MDA altitudes. Again, if the chart states uncompensated baro vnav, which I think they all do, or it is assumed uncomp. |
That is fine, as long as the ac system accepts the input. If it does not, and you are simply manually adding corrections, (not in the system) that is a problem. That means the ac thinks it it here, while you think it is there. Again, it depends on the level of automation and system capabilities. In your statement, who is providing or correcting the MSA temp? If your FCOM says no, I am not sure what the question is here. I would be curious what your SOP then uses as the temperature limit before you decide to correct? You with AC? We use tables (or these days the EFB for more accurate numbers) and add to step-down and FAF altitudes in the FMC. So that'd make it a manual entry. Where our SOP (and they changed recently) seem to differ from others is that FAF should be corrected when using VNAV minima, and you are within the temp limits for the procedure. I am aware of the FCOM SP.16, the EASA AMC, your POV as a procedure designer(?) but I just go by our OM-B. It tells us to correct FAF. Not really sure what the big problem is here. We correct up a bit, even if the path has been validated down to typically minus 20 C. So we come in slightly steeper, but not steeper than we would have on an ISA day. If temp is outside the limit for the procedure we fly it down to LNAV minima instead and keep correcting. Not with AC, but another northern carrier in Europe. We correct from 5 deg C (so ISA-10). That changed, we used to correct only from 0 deg C, after a 737 got a hard terrain warning approaching a level off altitude on a non-precision appr. It was a few degrees above zero and they hadn't corrected. They did come down pretty fast being a bit hot and high, but nothing out of the extreme ordinary. . |
Well, messing with manual additions in the FMS can have unintended consequences (as you illustrated)
A. Following the release of OPSB 0166-17 Rev 4 in December 2017, Rockwell Collins has continued to discuss this issue with the FAA. These discussions have resulted in the release of the following publications. The FAA performed a review of these documents and provided feedback on their content before release.
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When correcting DA or MDA for cold temperature I understand it is on the PFD, not on the FMC, that it is not allowed according to the manuals. From FAF/FAP onwards we are not allowed to modify anything, or else we are messing with the vertical path, that is clearly stated on the manuals (B737NG). the path calculated by the FMC should, as pointed out by some, take in account the worse case within the limits of temperature on the chart, but the Minima at which you initiate your Go around needs to be increased on your PFD. Do you correct DA for an ILS if it is -20C?, I take that the answer is a yes, same should be done for other type of approaches. |
Originally Posted by LEVC
(Post 10300409)
Do you correct DA for an ILS if it is -20C?, I take that the answer is a yes, same should be done for other type of approaches. |
When correcting DA or MDA for cold temperature I understand it is on the PFD, not on the FMC, that it is not allowed according to the manuals. We use tables (or these days the EFB for more accurate numbers) and add to step-down and FAF altitudes in the FMC. My understanding, and the procedure at a major UK operator with a large fleet of uncompensated B737s, is that you would fly the approach to LNAV/VNAV minima without any corrections provided the temperature was within the charted limit. 1. Our company applies cold temp corrections on baro-VNAV, as of recently, to all altitudes below temp corrected MSA. That includes, step-down altitudes, FAF, DA - despite what the FCOM Supp. Proc. says and the reference to AMC.CAT.OP.MPA. It is my understanding that you can fly it within the temperature limit stated on the chart, BUT the DA or MDA should be corrected because it is not taken in account when constructing the path, in fact you can use different minima depending on the onboard equipment and certification, the path flown will be the same whatever minima you use, and will be flatter if cold or steeper if warm, but the minima should be temperature corrected. Do you correct DA for an ILS if it is -20C?, I take that the answer is a yes, same should be done for other type of approaches. Holy :mad: what is going on up there?!?!?!?! When adjusted, they came in high and hot???? oh well, they landed....That seems okay? Adjust in PFD, FMC or well, somewhere? Where EXACTLY do you think the NA above and NA below temperatures come from? The DA/MDA NOT accounted for in the design??? Some adjust, some dont, some do it here, some do it there, some just think about it....no problems with the flightpath, obstacle clearances, missed approach, TCH, or min airspace separation???? Correct the MSA??? dont correct the MSA... What 1000 feet doesnt matter in the airspace? min sep???? This thread has been very enlightening on the basics of baro-vnav....damn. finally.....phew....it is just this simple... As stated by someone else before, AMC2 CAT.OP.MPA.126 is quite clear about this: For RNP APCH operations to LNAV/VNAV minima using Baro VNAV:
Again, procedures are designed with NA below at at 2.75 degree GPA (2.50 ICAO) and 3.5 GP NA above. NO correction to the DA/MDA.... |
underfire, I, too, am somewhat surprised by the variety of answers. Until recently we did not correct FAF. Now we do. The training department had a change of mind and I am quite sure they are knowledgeable about the AMC, the Boeing SP and general procedure design. What led them to that change, I do not know. I am still unsure as to why this is a big thing? We're putting the plane back onto a 3 degree path. Not that we need to, but we do. Correcting the DA is often no more than 50 ft, even on the coldest of days. If it's not necessary, as per procedure design, fine. Then we're just erring on the side of caution. Come to think of it, we used to have slightly different SOP for NPA-approaches (VOR, NDB), LNAV, VNAV and RNP AR. It was confusing and standardization was poor. Now we fly them the same way whether it's a VOR or RNP AR. It's a valid argument, I'd say. The MSA is part of your mental map of where you are. I don't go into Chicago, or New York, in blizzards with tight layers of traffic. Many of our destinations are fairly remote places, with terrain and cold temperatures. Separation to other traffic is not a factor. Descending procedurally on a FMC guided path is. Not correcting could be right out suicidal. And I am talking in general terms, not specifically about the VNAV approach. |
Some here must be quite happy to fly into terrain as long as they can quote the relevant AMC when asked at the pearly gates. Noone is advocating changing the FMC numbers beyond the FAF. We are simply saying “decide earlier”. This does not change the calculated or flown VNAV angle. |
N.b. IF you correct the FAF and then descend continiously on a 3 deg geometrical profile, then the raise of (D)DA does not move the intersect point away from the threshold, so one of the undesirable effects is well mitigated. If someone manages to merge the SOP for various NPA, err 2D approaches, into one drill for crews, it is a massive improvement on safety. The S word is being misapplied more often than not, but less workload and clearer standards is definitely the way to go. I can only imagine what a huge burden is lifted from the training system if the above is achieved. And how much good can be done with the freed-up resources! As for correcting the MSA: if left uncorrected, the nubmer loses its meaning completely. The connection between MSA and traffic separation is completely lost on this guy. |
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