Page 8 - Jan23T

Baro-VNAV Limits
The RNAV (GPS) RWY 18 approach (Figure 3) to Sedalia, Missouri (KDMO) shows a Baro-VNAV tem- perature limitation. When the ambient temperature is below -16 C (+3 F) or above 54 C (130 F), the LNAV/VNAV approaches are not authorized. I served at nearby White- man Air Force Base and my first flight instructor job was at Sedalia. It’s
not likely to get above 130 F, but there were many times (in that pre-GPS era) that the temperature was below 3 F.
Baro-VNAV and the VDP are both no authorized when using the Whiteman AFB altimeter setting, and night landings are not au- thorized on Runway 5/23.
Figure 3
glidepath using barometrically de- rived altitude information. But the FAA warns there may be temperature limitations on Baro-VNAV approaches. The Aeronautical Information Manual (AIM) tells us:
Hot and Cold Temperature Lim- itations. A minimum and maximum temperature limitation is published on procedures which authorize Baro- VNAV operation. These temperatures represent the airport temperature above or below which Baro-VNAV is not authorized to LNAV/VNAV minimums. As an example, the limita- tion will read: “Uncompensated Baro- VNAV NA below -8°C (+18°F) or above 47°C (117°F).” This information will be found in the upper left hand
box of the pilot briefing. When the temperature is above the high tem- perature or below the low tempera- ture limit, Baro-VNAV may be used to provide a stabilized descent to the LNAV MDA; however, extra caution should be used in the visual segment to ensure a vertical correction is not re- quired. If the VGSI is aligned with the published glidepath, and the aircraft instruments indicate on glidepath, an above or below glidepath indication on the VGSI may indicate that tempera- ture error is causing deviations to the glidepath. These deviations should be considered if the approach is contin- ued below the MDA.
NOTE: Many systems which apply Baro-VNAV temperature
compensation only correct for cold temperature. In this case, the high temperature limitation still applies. Also, temperature compensation may require activation by maintenance personnel during installation in or- der to be functional, even though the system has the feature. Some systems may have a temperature correction ca- pability, but correct the Baro-altimeter all the time, rather than just on the final, which would create conf licts with other aircraft if the feature were activated. Pilots should be aware of compensation capabilities of the sys- tem prior to disregarding the tempera- ture limitations.
There’s good news for pilots of WAAS GPS-equipped aircraft:
NOTE: Temperature limitations do not apply to flying the LNAV/ VNAV line of minima using approach certified WAAS receivers when LPV or LNAV/VNAV are annunciated to be available.
In other words, if you’re flying a GPS approach using a non-WAAS approach-certified GPS, watch for limitations on the use of the advisory glidepath in very hot or very cold con- ditions. If you’re using a WAAS GPS or the temperatures are not extreme, you’ll quickly dismiss this warning when you see it.
Other NAs
This is not an all-inclusive list of the procedures that may not be autho- rized for a given approach. Read the notes thoroughly as you brief for the approach. Remember, your success is in the details.
Won’t Controllers Protect Me?
Controllers won’t prevent you from trying to fly an unauthorized approach. According to the FAA’s guidance to controllers in Air Traffic Organization Policy JA 7110.65V, sec- tion 4-8-1 (with my emphasis add- ed in italics):
Approach clearances are issued based on known traffic. The receipt of an approach clearance does not relieve the pilot of his/her respon- sibility to comply with applicable
6 • TWIN & TURBINE / January 2023
NC-3, 01 DEC 2022 to 29 DEC 2022
NC-3, 01 DEC 2022 to 29 DEC 2022