Definition
A navigation system that computes a vertical glidepath on an instrument approach using altitude information derived from the aircraft's barometric altimeter rather than from satellite-based vertical guidance. It presents the pilot with a descent path that can be flown with reference to onboard equipment, provided the altimeter setting is current and the outside air temperature is within the approach's published limits.
Plain English
A way of showing the pilot a steady descent path during an approach, where the up-and-down position is worked out from the cabin pressure altimeter instead of from GPS height. As long as the altimeter setting is right and the air isn't too cold, it gives a smooth path down to the runway.
Context Anchor
Seen in instrument approach and WAAS discussions when comparing pressure-based vertical guidance with satellite-based vertical guidance.
Derivation
‘Barometric’ comes from the Greek baros meaning ‘weight,’ referring to the weight of the atmosphere measured by a barometer. ‘Vertical navigation’ simply means guidance in the up-down dimension. Together it signals that the vertical guidance is built from air-pressure measurements, not from satellites.
Why Pilots Care
Provides usable vertical guidance on approaches lacking WAAS vertical service, allowing stabilized descents and lower decision altitudes than step-down procedures.
Intuition Check
Do not assume barometric vertical navigation is satellite-measured height guidance. “Barometric” means the vertical guidance is based on air pressure, so pressure setting and temperature errors matter.
Example Sentence 1
On the RNAV approach into the mountain airport, the crew checked that the outside air temperature was above the chart's Baro-VNAV minimum before flying the LNAV/VNAV minimums.
Example Sentence 2
When WAAS vertical guidance was unavailable, barometric vertical navigation supplied the required descent profile to the runway.