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Can someone explain this paragraph from the A320 FCTM about minimum temperatures for non-precision approaches? I can't understand it.

COLD WEATHER OPERATIONS For all Non Precision Approaches, there is a minimum OAT. Below this temperature, the error on the barometric altitude is no longer acceptable, and altitude should be corrected in temperature. As it is not authorized to make these altitude corrections to the final approach segment of the FM Flight Plan (F-PLN) through the MCDU, it is not possible to use FINAL APP when OAT is below this minimum OAT. The flight crew must then use selected vertical guidance. This minimum OAT is indicated on the approach chart or must be defined by the operator based on the terrain profile (plus adequate margin).

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    $\begingroup$ Can you tell us which part you don't understand? This question explains the background about cold weather and approaches, but not the avionics part. $\endgroup$
    – Pondlife
    Commented Sep 24, 2017 at 18:37
  • $\begingroup$ I am surprised that there is not a max OAT, as that can be a factor as well. $\endgroup$
    – mongo
    Commented Sep 24, 2017 at 23:43
  • $\begingroup$ well, high OAT will just put you higher, so that's not really considered a big issue. other than a little extra energy descending on final you should be fine $\endgroup$
    – Radu094
    Commented Sep 25, 2017 at 7:02
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    $\begingroup$ Possible duplicate of Do instrument approach procedures sometimes have a minimum temperature? $\endgroup$
    – user14897
    Commented Sep 25, 2017 at 14:49

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I am not sure which part you don't understand, but here is my attempt to explain in more laymen terms.

Short version: When it is too cold, a certain mode for flying non-precision approaches using the Airbus flight computer cannot be used. This is because the altimeter reading is inaccurate when it is too cold, but the computer is not designed to compensate that.

Long version: For all non-precision approaches (i.e. approaches where ground equipment is not providing glideslope signal), there is a minimum Outside Air Temperature.

Since the reading of the barometric altimeter is affected by temperature, when it is too cold outside, the reading can no longer be considered accurate enough for the safety of flight. Corrections should be made (using a mechanical flight computer / lookup table / other tools) to convert the indicated altitude on the instrument to the reading it would have indicated under normal temperature.

Since it is not authorized to make these corrections in the autopilot computer, it is not possible to use the "FINAL APP" mode to fly the approach when the outside air temperature is below this minimum.

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  • $\begingroup$ I see got it 👍🏻 $\endgroup$
    – Jai
    Commented Sep 25, 2017 at 7:18

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