RNP

[FR9999]

Hi guys,

Im sorry the following question may sound stupid, but English is not my native language and I just cant get my head around the following sentence find on a lot of GNSS approaches.

"Uncompensated BARO VNAV NA below -10°c"

How to interpret this?

Thanks

[underfire]

It means you cannot use the procedure if the temperature is below 10°C

As temperature is dropping, the actual altitude vs reported altitude is dropping.

For non comp baro, you will be lower on the glideslope, thus losing the obstacle clearance. http://code7700.com/altimeter_temperature_correction.html

http://code7700.com/images/altimeter_temperature_correction_example.png

[Matey]

It means that, if the temperature is below the published minimum and you are operating in an aircraft with an uncompensated system (B737 is one), then you cannot operate to the published VNAV minima (LNAV/VNAV minima on a Jeppesen chart.) You can still fly the procedure, but to LNAV minima only, and with appropriate cold temperature corrections applied. The corrections will reinstate the aircraft at the correct true barometric altitude (3500 in underfire's example above), whilst actually reading a higher indicated altitude on your altimeter.

[oggers]

"Uncompensated BARO VNAV NA below -10°c"

NA = Not Authorised

[FR9999]

Thank you guys for your time. I really do appreciate it. So as I understand, you dont have to apply a temperature correction to this LNAV/VNAV minima in this case?

[FlightDetent]

VNAV is driven by the machine, being out of temperature envelope legally precludes you from using it. Therefore the VNAV/LNAV minima are N/A too.

One would fly plain LNAV approach i.a.w. the DIST/ALT table, having applied the temp correction to the declared values. Down to plain LNAV minima that need to be corrected upwards too! See Matey above.

my 2c, FD.

[oggers]

FR9999, you do have to apply temperature correction to the minima. It is the pilot's responsibility to make a temperature correction whenever it is 'very cold'. 'Very cold' translates to an airfield temperature of <0°C generally, or for the US a temperature published on the plate for certain airports. The temperature correction to procedure minima applies to all procedures including those made using compensated Baro VNAV.

The webpage that underfire linked to offers a good explanation and references for all of this.