Final Aib world

[michelda]

Hi all,

I’m flying a GNSS approach on FINAL mode down to vnav minima. Actual OAT is above the minimum temperature reported on chart.
OAT is below 0 C do I need to correct the minima?

thanks,
if you have the reference it’s better

D.

[Banana Joe]

No, you must not apply any correction to the VNAV minima. If the temperature is below the minimum temperature for the associated procedure, you apply the temperature correction to the LNAV minima but you can fly it with VNAV PTH if your SOPs allow it.

https://skybrary.aero/bookshelf/books/2315.pdf

[Capt Scribble]

If the temp is lower than that on the plate, you are not permitted to fly the procedure (with those minimums). If the approach is within the temp limits, look to see what it says in your SOPs in regard to temp error corrections. There has been much discussion in the past on here. I saw a reference given that said no temp corr required, but my Co’s SOP required one to be applied to procedural alts, minimum alts and go around alts (but you must tell ATC if you are radar controlled).
https://www.pprune.org/tech-log/623584-cold-temp-barovnav-easa-language.html?highlight=Temperature+corrections

[FlightDetent]

Banana Joe is correct. The question is well placed, however.

Let's say for -10 degrees you'd be flying inside the temp envelope for the procedure, designer's work protects you from the obstacles. But your on-board altimeter mis-indicates due to cold temperature error (ISA-25). So home come do not need to increase the minima (moreover, the correct wording is must not increase)? After all, Doc 8168 tells you to compensate for that and the geometry is rather clear - don't correct = get below. Hm?

Nice catch.

Short review: the Operator minima altitude is the operators' add-on PLUS [the higher of (obstacle elevation + minimum obstacle clearance);(system minima)]

A) Hence in a case where the minima are restricted by the obstacle, the OCA = ELEV + MOC is calculated by the designer with non-compensated baro already accounted for down to the low temp limit.
B) If there are no /low obstacles and the lowest system minima (arbitrary number) defines the value, there are no obstacles to hit by definition.

Wait, the "b" above would work, but in aviation is just plain wrong just by the sound of it. Being clear of the terrain does not make it right. Plus, how do you justify being lower than the minima as that's where the altimeter will take you?

Answer: Lesser of two evils.

If you would compensate the minima while flying a not-compensated profile as authorised by the temperature envelope, you'd effectively move the point of reaching that minima further from the runway. This will invalidate the RVR / VIS calculation and might have detrimental effects on the safety level end economy.

Then: As you are always safe from obstacles by the full prescribed margin with altimeter error already accounted for (OCA by procedure design in case A), it is accepted to have MDA geometrically lower then system minima (case B) for the sake of retaining RVR/VIS values and increasing the likelyhood of obtaining sufficient visual reference.

Capt Scribble Many operators require correcting the MisAp alt, without seeing that by definition is not a minimum altitude but a maximum "climb-to" altitude.

[michelda]

Thanks guys but still I have few doubts.

basically flying vnav or worse scenario flying lpv approach without minima correction, I’ll start the missed approach at lower altitude and probably outside the obstacle margin envelope (Theoretically).

the lvp approach is basically an “ils approach” (Most of the time with same minima) so why I have to correct the minima in one side and no in the other?

thanks

[FlightDetent]

Thanks guys but still I have few doubts.

basically flying vnav or worse scenario flying lpv approach without minima correction, I’ll start the missed approach at lower altitude and probably outside the obstacle margin envelope (Theoretically).

the lvp approach is basically an “ils approach” (Most of the time with same minima) so why I have to correct the minima in one side and no in the other?

thanks

No. Obstacle clearance is always assured by the virtue of OCH calculation.

BaroAPV is very different from ILS, since in cold air you will fly authotized but still on a flatter angle. And that is wwhen raising minima up to the geometrical value would bite.

[deltahotel]

Hi.

1. LVP is not an ILS. It’s a PBN approach with lower minima because it has more accuracy due to correction from an external source. eg WAAS, EGNOS etc

2. Correct the minima for any approach for low temps.

HtH

[FlightDetent]

2. Correct the minima for every approach for low temps. Careful, please. My bolding.


AMC2 CAT.OP.MPA.126 Performance-based navigation
(d) Altimetry settings for RNP APCH operations using Baro VNAV
(2) Temperature compensation
(i) For RNP APCH operations to LNAV/VNAV minima using Baro VNAV:
(B) when the temperature is within promulgated limits, the flight crew should not make compensation to the altitude at the FAF and DA/H;

[Capt Scribble]

Some guidance from Jeppeson, page 8 para a seems relevant.
http://www.jeppesen.com/download/briefbull/den00-arnav.pdf

[FlightDetent]

The French CAA document Banana Joe linked in post #3 is excellent. 7.5.2 through 7.5.3.

[michelda]

Thanks to everybody,

FlightDetent..I read that amc but what’s your interpretation of the amc2 spa.pbn.105(d) point (j)?

D.

[FlightDetent]

That it fits my explanation and reasoning behind it (which I borrowed somewhere on this site) perfectly. The DGAC paper in 7.5.4. note 2 tells you the same.

What I haven't seen yet, that if you are flying inside the temp envelope on the cold side, is it permissible to use the compensation function in the avionics? It's a trick question.

[turbidus]

Does the chart say uncompensated baro vnav? Pretty sure that means all of the information in the chart is based on uncompensated, with the NA above/below temperatures built into the obstacle clearance areas and the DA/MDA...

From what I remember, if the chart says uncompensated, you fly uncompensated...

If you want to compensate, you must inform ATC and seek permission. It is usually no, as the means and methods of compensation are varied, and most dont understand where and when to add. The compensation factors can lead to loss of separation if applied randomly. This can happen by a number of factors, as some ac have a compensation feature, while others do not...

[FlightDetent]

Not speaking about the altitude to FAF per se, rather about the profile / angle after FAF. My machine does not have such feature, hence the child-like question. The key word in it was permissible, mind you. From the regs I've noticed so far, there is no guidance and no exclusion. Somehow I feel it might cause more troubles than bring solutions.

[deltahotel]

Well it’s a mess, isn’t it. Plenty of conflicting information from too many sources. FAA makes reference to applying temperature corrections , as does PANSOPS. Other sources don’t appear to and there seems to be some conflict between the meanings of compensation (FMC) and correction.

Intuition, experience and logic would say that if a known error can be corrected for then it should be, so in the meantime I’ll continue to use my airline’s SOP which is to apply temperature error correction for all approaches when the airfield temp drops below 0.

Stay safe, all

[FlightDetent]

experience and logic would say that if a known error can be corrected for then it should be, so in the meantime I’ll continue to use my airline’s SOP which is to apply temperature error correction for all approaches when the airfield temp drops below 0. Used to do the same until CAA audit came and overruled the SOPs with the EASA paragraph linked above, which says the opposite. I can't blame them from throwing the book around, yet struggle to see the benefit of making things less clear and more complex.

[Skyjob]

The difference is in the procedure design.
For LNAV/VNAV approaches, no changes are made to the coded crossing altitudes, procedure temperature restrictions are in place to mitigate flying a flatter profile.
For all approaches minima on the altitude reference are corrected for cold weather operations, including LNAV/VNAV minima, as they are correcting for lowest altitude above ground to make a decision, nothing to do with coding of the approach.

So:

if you fly an ILS, you correct all altitudes as the angle is fixed;
if you fly APV or LNAV/VNAV, you do not correct altitudes coded for the profile as they are protected by temperature usage on the chart;
if you fly any approach below 0 C you must use temperature corrections for the minima on the reference selector as this is read by temperature prone instruments (altimeter).
if you fly to a DA based on RAD ALT, this temperature correction is not required s this instrument is not prone to temperature errors (hence no correction for LVP using RAD ALT

[FlightDetent]

Would somebody kindly tell the gentleman above, that he’s wrong on bullet point 3 - for APV baro-VNAV within the promulgated temperature envelope?

[Skyjob]

Would somebody kindly tell the gentleman above, that he’s wrong on bullet point 3 - for APV baro-VNAV within the promulgated temperature envelope?
You are indeed correct, apologies

[FlightDetent]

I was banging the wrong drum with vigour for at least 4 years, through all the threads
https://www.pprune.org/tech-log/607100-lnav-vnav-barovnav-approach.html,
https://www.pprune.org/tech-log/601732-cold-temp-corrections-lnav-appr-2.html
https://www.pprune.org/tech-log/601732-cold-temp-corrections-lnav-appr.html

ignoring all the good advice from aterpster, underfire and countless others. Until FlyingStone force-opened my skull here https://www.pprune.org/tech-log/614852-temperature-correction-baro-vnav-approach.html#post10295989. You may have been there all along. :)

Sorry for being rude with my previous remark.