VNAV approach guidance to a DA is not authorized if the reported surface temperature is what?

VNAV (Vertical Navigation) approach guidance to a Decision Altitude (DA) is dependent on specific temperature limitations to ensure safe operations. The correct answer indicates that if the reported surface temperature is below the Baro-VNAV minimum temperature limitation, then VNAV guidance is not authorized for the approach.

Baro-VNAV systems require a minimum temperature for accurate altitude calculations and performance. When temperatures fall below these minimums, there is a risk of unreliable altimeter readings and potential anomalies in vertical guidance during the approach, which can compromise safety. Therefore, adherence to these temperature limitations is crucial, and flying below the established minimums is not allowed because it could result in inaccurate altitude information and unsafe approach conditions.

The other temperature scenarios mentioned do not directly address the critical nature of operating within the specified minimum temperature limit, which governs the safety and reliability of the VNAV approach.