B737NG Vertical NPS scales

[Pin Head]

Hi

The default value is 125fpm on the vertical scale.

Can I ask were this value comes from? There is a reason as years ago heard some refer to it.

Thanks

[victorpapa]

From FCTM
For airplanes with NPS, the flight crew may​ enter 125 feet for vertical RNP. While ​there are no vertical RNP​ values published on the approach chart, the use of 125 ​feet will cause the NPS amber deviation exceedance alert to​ occur at 75 feet or ​slightly​ less deviation, since vertical​ ANP​ will be at least 50 feet at all times.​

[Sciolistes]

And 75 feet is the vertical deviation limit for RNP approaches.

[aterpster]

The Baro VNAV Vertical Error Budget (VEB) gets smaller with lower RNP minimums; i.e. 0.10 or 0.20 vice 0.30. The scaling should follow suit for the final approach segment.