Approaches (Part Fourteen)

Baro-VNAV

Baro-VNAV is an RNAV system function that uses barometric altitude information from the aircraft’s altimeter to compute and present a vertical guidance path to the pilot. The specified vertical path is computed as a geometric path, typically computed between two waypoints or an angle based computation from a single waypoint. Operational approval must also be obtained for Baro− VNAV systems to operate to the LNAV/VNAV minimums. Baro−VNAV may not be authorized on some approaches due to other factors, such as no local altimeter source being available. Baro−VNAV is not authorized on LPV procedures.

 

For the RNAV (GPS) RWY 30 approach, the note “DME/ DME RNP-0.3 NA” prohibits aircraft that use only DME/ DME sensors for RNAV from conducting the approach. [Figure 4-16]

Figure 4-16. North Platte Regional (KLBF), North Platte, Nebraska, RNAV (GPS) RWY 30.

Figure 4-16. North Platte Regional (KLBF), North Platte, Nebraska, RNAV (GPS) RWY 30.

Because these procedures can be flown with an approach approved RNP system and “RNP” is not sensor specific, it was necessary to add this note to make it clear that those aircraft deriving RNP 0.3 using DME/DME only are not authorized to conduct the procedure.

The least accurate sensor authorized for RNP navigation is DME/DME. The necessary DME NAVAID ground infrastructure may or may not be available at the airport of intended landing. The procedure designer has a computer program for determining the usability of DME based on geometry and coverage. Where FAA flight inspection successfully determines that the coverage and accuracy of DME facilities support RNP, and that the DME signal meets inspection tolerances, although there are none currently published, the note “DME/DME RNP 0.3 Authorized” would be charted. Where DME facility availability is a factor, the note would read, “DME/DME RNP 0.3 Authorized; ABC and XYZ required,”meaning that ABC and XYZ DME facilities are required to assure RNP 0.3.

 

Hot and Cold Temperature Limitations

A minimum and maximum temperature limitation is published on procedures that authorize Baro−VNAV operation. These temperatures represent the airport temperature above or below which Baro−VNAV is not authorized to LNAV/VNAV minimums unless temperature compensation can be accomplished. As an example, the limitation will read, uncompensated Baro−VNAV NA below −11 °C (12 °F) or above 49 °C (120 °F). [Figure 4-15] This information will be found in the upper left hand box of the pilot briefing. When the temperature is above the high temperature or below the low temperature 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 required. If the VGSI is aligned with the published glide path, and the aircraft instruments indicate on glide path, an above or below glide path indication on the VGSI may indicate that temperature error is causing deviations to the glide path. These deviations should be considered if the approach is continued below the MDA.

Figure 4-15. RNAV RNP approach procedure with curved flight tracks.

Figure 4-15. RNAV RNP approach procedure with curved flight tracks.

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 order to be functional, even though the system has the feature. Some systems may have a temperature correction capability, but correct the Baro−altimeter all the time, rather than just on the final, which would create conflicts with other aircraft if the feature were activated. Pilots should be aware of compensation capabilities of the system prior to disregarding the temperature limitations. The information can be seen in the notes section in Figure 4-16.

In response to aviation industry concerns over cold weather altimetry errors, the FAA conducted a risk analysis to determine if current 14 CFR Part 97 instrument approach procedures, in the NAS place aircraft at risk during cold temperature operations. This study applied the coldest recorded temperature at the given airports in the last five years and specifically determined if there was a probability that during these non-standard day operations, anticipated altitude errors in a barometric altimetry system could exceed the Required Obstacle Clearance (ROC) used on procedure segment altitudes. If a probability of the ROC being exceeded went above one percent on a segment of the approach, a temperature restriction was applied to that segment. In addition to the low probability that these procedures will be required, the probability of the ROC being exceeded precisely at an obstacle position is extremely low, providing an even greater safety margin.

 

Pilots need to make an altitude correction to the published, “at”, “at or above” and “at or below” altitudes on designated segment(s) of IAPs listed at specific airports, on all published procedures and runways, when the reported airport temperature is at or below the published airport cold temperature restriction.

This list may also be found at the bottom of the, “Terminal Procedures Basic Search” page found at: http://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dtpp/ search/

Pilots without temperature compensating aircraft are responsible to calculate and make a manual cold-temperature altitude correction to the designated segment(s) of the approach using the AIM 7-2-3, ICAO Cold Temperature Error Table.

No extrapolation above the 5000 ft column required. Pilots should use the 5000 feet “height above airport in feet” column for calculating corrections of greater than 5000 feet above reporting station. Pilots will add correction(s) from the table to the segment altitude(s) and fly at the new corrected altitude. PILOTS SHOULD NOT MAKE AN ALTIMETER CHANGE to accomplish an altitude correction.

Pilots with temperature compensating aircraft must ensure the system is on and operating for each segment requiring an altitude correction. Pilots must ensure they are flying at corrected altitude. If the system is not operating, the pilot is responsible to calculate and apply a manual cold weather altitude correction using the AIM 7-2-3 ICAO Cold Temperature Error Table.

Pilots must report cold temperature corrected altitudes to Air Traffic Control (ATC) whenever applying a cold temperature correction on an intermediate segment and/ or a published missed approach final altitude. This should be done on initial radio contact with the ATC issuing approach clearance. ATC requires this information in order to ensure appropriate vertical separation between known traffic. ATC will not beproviding a cold temperature correction to Minimum Vectoring Altitudes (MVA). Pilots must not apply cold temperature compensation to ATC assigned altitudes or when flying on radar vectors in lieu of a published missed approach procedure unless cleared by ATC.

 

Pilots should query ATC when vectors to an intermediate segment are lower than the requested intermediate segment altitude corrected for temperature. Pilots are encouraged to self-announce corrected altitude when flying into uncontrolled airfields.

The following are examples of appropriate pilot-to-ATC communication when applying cold-temperature altitude corrections:

On initial check-in with ATC providing approach clearance: Hayden, CO (example below).

Intermediate segment: “Require 10600 ft. for cold temperature operations until BEEAR”,

Missed Approach segment: “Require final holding altitude, 10600 ft. on missed approach for cold temperature operations”

Pilots cleared by ATC for an instrument approach procedure; “Cleared the RNAV RWY 28 approach (from any IAF)”. Hayden, CO (example below).

Intermediate Segment: “Level 10600 ft for cold temperature operations inside HIPNA to BEEAR”

Pilots are not required to advise ATC if correcting on the final segment only. Pilots must use the corrected MDA or DA/DH as the minimum for an approach. Pilots must meet the requirements in 14 CFR Part 91.175 in order to operate below the corrected MDA or DA/DH. Pilots must see and avoid obstacles when descending below the MDA. The temperature restriction at a “Cold Temperature Restricted Airport” is mutually exclusive from the charted temperature restriction published for “uncompensated baro-VNAV systems” on 14 CFR Part 97 RNAV (GPS) and RNAV (RNP) approach charts. The charted temperature restriction for uncompensated baro-VNAV systems is applicable to the final segment LNAV/VNAV minima. The charted temperature restriction must be followed regardless of the cold temperature restricted airport temperature.

Pilots are not required to calculate a cold temperature altitude correction at any airport with a runway length of 2,500 feet or greater that is not included in the airports list found at the URL above. Pilots operating into an airport with a runway length less than 2,500 feet, may make a cold temperature altitude correction in cold temperature conditions.

Cold Temperature Restricted Airports: These airports are listed in the FAA Notices To Airmen Publication (NTAP) found here: https://www.faa.gov/air_traffic/publications/notices/.

Airports are listed by ICAO code, Airport Name, Temperature Restriction in Celsius/Fahrenheit and affected Segment. One temperature may apply to multiple segments. Italicized airports have two affected segments, each with a different temperature restrictions. The warmest temperature will be indicated on Airport IAPs next to a snowflake symbol (see below), in the United States Terminal Procedure Publication. The ICON will be added to the TPPs incrementally each charting cycle.