For example, performing a Baro-VNAV approach during a hot day would result in
guidance relative to a glide path angle steeper than the published glide path angle.
On the contrary, during a cold day, a Baro-VNAV approach would be based on
guidance relative to a glide path smoother than the published glide path angle.
The approach plates indicate a temperature range for which the approach has
been designed.
Within this temperature range, the LNAV/VNAV can be used with uncompensated
Baro-VNAV systems.
Outside of this temperature range, LNAV/VNAV minimums shall not be used with
uncompensated Baro-VNAV systems.
The Garmin approach Baro-VNAV system is automatically temperature-
compensated to produce a glidepath position in space such that Baro-VNAV
approaches are always flown at the published glide path angle when the actual
temperature deviates from the ISA model. This produces results similar to ILS
glideslopes and LPV glide-paths that remain in the same position in space without
respect to temperature.
To produce the correct geometric glide path angle on the final approach segment,
temperature compensation is applied to the barometric altitude and used to
determine the displayed vertical deviation.
However, the altimeter continues to display uncompensated barometric altitude.
The temperature compensation required depends on the temperature profile over
the altitude range between the point at which the barometric setting is measured
(presumed to be the approach airport) and the present altitude of the airplane.
This temperature profile is estimated by using the air data system static air
temperature (SAT) and applying the standard temperature lapse rate to determine
the temperature over the rest of the range.
When using barometric altitude for vertical guidance along the final approach
segment, temperature compensation is applied whether the temperature is above
or below standard temperature. The actual compensated altitude is not displayed
to the pilot during an approach.
Compensating Waypoint Altitudes
Depending on the terrain, temperature compensation may be required for
waypoints in the approach prior to the final approach segment due to terrain
and/or obstacle clearance requirements.
Temperature Compensation of Approach Minimums
Section 7
Description
Pilot's Information Manual
PIM TBM 960 - Edition 0
Rev. 01
Page 7.15.11
PIM - DO NOT USE FOR FLIGHT OPERATIONS
