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RNP approaches. A question about the APV version and low temperature

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RNP approaches. A question about the APV version and low temperature

Old 3rd Dec 2018, 12:20
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RNP approaches. A question about the APV version and low temperature

Fellow aviators,


I try to come to a full understanding of the RNP APV (LNAV/VNAV) approaches and I am still lacking some understanding… Who can help me out here?

In ICAO doc 8168 II.1.4.1 it says:
1.4.1 Pilots are responsible for any necessary cold temperature corrections to all published minimum altitudes/heights. This includes:
a) the altitudes/heights for the initial and intermediate segment(s);
b) the DA/H; and
c) subsequent missed approach altitudes/heights.
Note.— The final approach path vertical path angle (VPA) is safeguarded against the effects of low temperature by the design of the procedure.

I am looking specifically at the correction for the DA.
The EASA AIR OPS AMC2 SPO.OP.116 2(i)(a) says for a RNP APCH LNAV/VNVAV:

when the temperature is within promulgated limits, the flight crew should not make compensation to the altitude at the FAF and DA/H; and

As I interpret this, there is a difference between ICAO and EASA. Anyone who can shine a light on this?

Regards,
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Old 3rd Dec 2018, 13:32
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Discussed here, I think the general opinion was, do what is says in your Ops manual!
Cold temperature corrections on LNAV/VNAV minima
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Old 3rd Dec 2018, 14:45
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Note.— The final approach path vertical path angle (VPA) is safeguarded against the effects of low temperature by the design of the procedure.
when the temperature is within promulgated limits, the flight crew should not make compensation to the altitude at the FAF and DA/H; and
Technically, these are saying the same thing....

and yes, when a temperature correction is required, the pilot is responsible, but it must be cleared with ATC or you dont use the procedure.

It is discussed in detail at the link Capt S provided.
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Old 3rd Dec 2018, 16:34
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Originally Posted by underfire View Post
Technically, these are saying the same thing....

and yes, when a temperature correction is required, the pilot is responsible, but it must be cleared with ATC or you dont use the procedure.

It is discussed in detail at the link Capt S provided.
Technically they are not the same thing. APV has a geometrical descent path, whereas an RNP approach to LNAV/VNAV minima has a path based on barometric data. Therefore, the APV is in the regard to low temp correction more akin to other geometric approaches, like ILS and GLS approaches. The LNAV/VNAV one however is not, its approach path will change with temperature, it is just designed to be safe within the published temperature limit without adjusting the DA, whereas on a geometric path correction is absolutely necessary.
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Old 4th Dec 2018, 15:13
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Sorry, didnt notice APV in the question.
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Old 5th Dec 2018, 16:09
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Capt Scribble, thanks for the link. As you said, do what your manual says. No argument about that. I just like to know where the difference is coming from.

Denti, thanks for pointing out the difference APV, and lnav/vnav.

According EASA the design of the procedure is including the cold temperature effect in de DA for the lnav/vnav when within the temperature range. ICAO suggests it is not. My question is just a basic question about the design of the procedure. But apparently difficult to find an answer for.

Other question, same topic:

What if the OCA is raised by NOTAM to a value in excess of the original DA? Should you raise the new DA to a value equal to the NOTAM OCA and does this OCA then include the cold temperature correction as the DA does? Or should for a case like this specifically a new DA be promulgated?
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Old 6th Dec 2018, 10:11
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Apologies for the thread drift, but can anyone enlighten us on the effect low temperature has on the A320 FPV. Most folks believe that it is purely IRS derived, but it has a barometric input too which must be affected by temperature.
I tried following the ILS GP in ISA -20 using the FPV and it appeared that around -3.7 was selected to maintain the GP but the actual FPV appeared to be indicating less than that. The sim was a CAE device recently upgraded to 1.9.
Any ideas?
Cheers all
mcdhu
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Old 6th Dec 2018, 22:50
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Originally Posted by mcdhu View Post
Apologies for the thread drift, but can anyone enlighten us on the effect low temperature has on the A320 FPV. Most folks believe that it is purely IRS derived, but it has a barometric input too which must be affected by temperature.
I tried following the ILS GP in ISA -20 using the FPV and it appeared that around -3.7 was selected to maintain the GP but the actual FPV appeared to be indicating less than that. The sim was a CAE device recently upgraded to 1.9.
Any ideas?
Cheers all
mcdhu
Yes. The FPA is computed by inertial (GS) and barometric data (baro rate of descent) and it is ISA referenced.

What you noticed is correct.
In cold temperatures the ADIRS sense higher altitudes and thus steeper calculated paths have to be flown by the pilot to compensate this effect.

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Old 7th Dec 2018, 00:31
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[QUOTE]Apologies for the thread drift, but can anyone enlighten us on the effect low temperature has on the A320 FPV. Most folks believe that it is purely IRS derived, but it has a barometric input too which must be affected by temperature.

Of course the barometric input is affected. Depending on the ac, that is where the IRU gets the data from.

tried following the ILS GP in ISA -20 using the FPV and it appeared that around -3.7 was selected to maintain the GP but the actual FPV appeared to be indicating less than that. The sim was a CAE device recently upgraded to 1.9.
ILS is not affected by temperature. FPV ?? I thought even Boeing states not to rely on that...

Bottom line, the procedures are designed NOT to be corrected if within the posted temperature limits.

Last edited by underfire; 7th Dec 2018 at 01:09.
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