RNAV approaches

Read each RNAV line as a different operation

An RNAV (GPS) chart can publish several lines. They do not all become available merely because the procedure loads. Read the approved installation capability and actual service annunciation, then select the matching published line and category. Equipment, local restrictions, notices, visibility and usable altimeter source must support that operation.

LP is not LPV without the glidepath and is not an automatic fallback from LPV. It must be published and supported; some older LPV receivers lack LP approval. LPV and LNAV/VNAV are approaches with vertical guidance (APV) in FAA/ICAO terminology, rather than ICAO precision approaches. Current ACS Appendix 3 uses approved vertical guidance to a DA for Task B preparation; that does not make every APV formally an ILS-style precision procedure.

A lower printed MDA on another line does not make it interchangeable with a DA. Obstacle assessment and operational conditions differ. Select an operation deliberately, brief its minimum and restrictions, and stay with a usable supported procedure.

AIM 5-4-5: RNAV chart lines and APV terminology · AIM 1-1-18: WAAS capability, LP and service annunciations · ACS Appendix 3, printed 33–34: MDA/approved-vertical DA approach tasks

Verify capability and the named procedure

Confirm aircraft installation and operating approval in the AFM/POH supplement, not just a receiver’s marketing description or TSO label. Review supported approach types, sensors, limitations, database requirements and any required pilot training/authorization. Portable/VFR GPS and tablet position are situational aids, not approved final guidance. RNAV (RNP) authorization-required operations, RF-leg capability and their special approvals must not be inferred from RNAV (GPS) approval.

Retrieve the exact named approach and assigned transition from the appropriate current airborne navigation database. Compare airport/runway, suffix, fixes, leg order, courses, altitude constraints and missed with the current chart/NOTAMs. The procedure must be available by name; constructing an approach from manually entered coordinates or bearing/distance fixes is not permitted. Do not modify protected final legs or use Direct To to skip a required segment. Review database discrepancies before flight; a map that merely depicts a conventional procedure does not make it an authorized GPS approach.

Loading places a procedure in the flight plan; activation and sequencing determine what the system will navigate. Verify active leg, source, direction and expected turn behavior. Select a transition matching the clearance. A vectors-to-final selection can omit earlier fixes and increase reprogramming workload when ATC later clears to one of them. Know the actual installation’s behavior and request time or revised routing when needed.

AIM 1-1-17: approach installation/data approval and named retrieval · AIM 1-1-18: WAAS AFM/supplement requirements · AIM 5-4-6: cleared entry, RF capability and vectors-to-final cautions · IPH Chapter 6, printed 6-14–6-17: chart/database discrepancies

Prove the supported mode before descending

Before final, confirm the actual GPS/RNAV source, active final leg, supported approach level, approach activation, integrity and appropriate sensitivity. An armed procedure or a magenta course line is not proof of valid final mode. Labels, messages, source switching and autopilot capture differ by installation; train with the actual supplement. If the system cannot meet the needed final operation, do not descend as though it can.

For basic GPS LNAV equipment, the current AIM describes sensitivity changing from terminal ±1 NM to final ±0.3 NM as the approach becomes active near the final approach waypoint. WAAS LP/LPV final guidance uses different, angular behavior. Do not treat one dot as a constant distance for all modes. A sensitivity change can make an existing displacement look larger; monitor track/cross-track trend and use small corrections rather than chasing it.

Comply with entry/initial/intermediate restrictions even when a glidepath is displayed early. Outside final, approved vertical guidance does not waive crossing limits. Within final, LNAV-only stepdowns do not apply to a supported approved LPV/LNAV/VNAV DA path flown on its valid vertical guidance; they do apply when flying LNAV/LP MDA operations. Configure and stabilize in time, use a planned initial descent rate appropriate to actual angle/groundspeed, and continuously cross-check airspeed, altitude, mode, integrity and path.

AIM 1-1-17: approach activation, sensitivity and FAWP checks · AIM 1-1-18: WAAS approach service selection and angular guidance · AIM 5-4-5: outside-final and MDA-only final stepdowns · ACS VI.B.K2/K4, printed 15–16

A descent cue does not grant a lower operation

Approved LPV or LNAV/VNAV service provides a final glidepath to the published DA when the installation and procedure conditions are met. An advisory cue on LNAV or LP is a planning/control aid. Manufacturer labels such as “LNAV+V” or “LP+V” must be interpreted through that installation’s documentation: the plus sign does not create another FAA minima line or convert MDA to DA.

When using advisory guidance, protect each stepdown and MDA, assess any VDP, and plan a CDFA decision high enough to avoid going below MDA during a missed transition. A VDA or advisory cue does not ensure obstacle clearance below MDA. With approved vertical guidance, make the decision promptly at the correct DA; do not level there or continue searching without the required conditions.

Both kinds of operation need §91.175 normal-descent position, flight visibility and a listed identifiable reference before continuing below minimums. All three conditions remain independent. Review the MDA technique in Approaches without vertical guidance and the DA visual transition in ILS approaches.

AIM 5-4-5: RNAV minima, VDA and VDP · AIM 1-1-18: WAAS announced level of service · AC 120-108A §3.7–3.8: MDA/DDA technique · 14 CFR §91.175(c)–(e): cumulative visual conditions

Prepare for an unavailable or lost service

Review GPS/WAAS and procedure NOTAMs and the prediction/integrity requirements for the actual installation. A basic GPS RAIM prediction is a planning check, not proof of in-flight integrity. A receiver can show plausible position while required integrity is unavailable. If RAIM/approach activation is not available before final, do not begin the final descent; follow the approved failure procedure and obtain a usable alternative. A required lateral-integrity alarm during final demands prompt appropriate missed/failure action.

WAAS announces the supported published service. Current AIM cautions that receivers do not automatically “fail down” to lower levels after approach activation. A vertical-only off flag may permit use of LNAV minima when the rules and actual installation permit a change, but the pilot must still meet LNAV restrictions, MDA, visibility and a stable supported path. A late loss below the usable MDA or with no time to rebuild the operation is not permission to keep descending. Loss of lateral integrity on LP requires a missed; there is no active-approach reset to a looser limit.

If only LNAV is available before final, consciously rebrief it if usable; otherwise choose another approach. If a better level returns, do not assume the active approach upgrades: the current AIM says a more accurate service cannot return until the next activation. Report unexpected GNSS anomalies promptly using current guidance when workload permits, state remaining capability, and use real AFM/supplement failure actions. An autopilot follows the selected guidance; it does not restore integrity.

AIM 1-1-17: RAIM/approach failure action and GNSS reporting · AIM 1-1-18: active-approach service/vertical flag/lateral integrity limitations · 14 CFR §91.187: equipment-malfunction reporting

Treat Baro-VNAV as an altitude-sensitive system

Baro-VNAV uses barometric altitude for approved vertical guidance. An incorrect altimeter setting can create an incorrect vertical path even while lateral GPS position is accurate. Current AIM requires a local altimeter setting for Baro-VNAV. If the local setting is unavailable, an authorized remote-setting note does not make Baro-VNAV usable. An approved WAAS LNAV/VNAV operation may remain available using a chart-authorized nonlocal setting and its required raised minima.

Read the exact uncompensated Baro-VNAV temperature range. On an RNAV (GPS) chart it restricts the LNAV/VNAV Baro-VNAV operation outside that range unless the approved temperature-compensation capability/procedure applies. It does not, by itself, prohibit WAAS geometric LPV or WAAS LNAV/VNAV merely because the temperature is outside the Baro range. On RNAV (RNP) procedures, the uncompensated range can apply to the entire procedure; those authorization/capability requirements require separate training.

Cold barometric altimetry puts true altitude below indicated, and uncompensated Baro-VNAV can produce a shallower true path; warmth has the opposite path effect. Do not invent compensation by changing pressure setting or editing a protected glidepath. Use the approved system’s method and scope. The Baro-VNAV range and the Cold Temperature Airport snowflake procedure are separate requirements and may both apply.

AIM 5-4-5: local/nonlocal setting and Baro-VNAV restrictions · AIM 7-3-3: uncompensated Baro-VNAV range and geometric-guidance distinction · IPH Chapter 4, printed 4-31: Baro-VNAV operational principles

Correct barometric altitudes when CTA rules apply

A snowflake and temperature on an FAA approach identify a Cold Temperature Airport (CTA). At or below the published trigger, apply the current AIM method to the affected approach segments. Use the current CTA list for an individual-segment method, or follow the all-segments method and its specified calculation. The table uses reported airport temperature and height above airport, not MSL altitude alone. Check compensation capability from the actual supplement; some systems do not correct DA/MDA, or only correct loaded procedure altitudes.

Keep the current pressure setting. Add the applicable correction to the altitude to fly; do not change the altimeter setting to implement temperature correction. For the DA/MDA correction, use the calculated value or round up, never down. Request ATC approval on initial contact (or as soon as practical) for applicable CTA corrections outside the final segment, and advise the corrected altitudes under the current AIM procedures. Approval is also required before correcting any ATC-assigned altitude. No final-segment correction report is required. Under the specified table/segment methods, the missed correction applies to the final missed holding altitude, not generically to every missed turn/climb gate. Do not apply these CTA corrections to SID, ODP or STAR altitudes.

ILS and WAAS geometric paths are not bent by cold temperature, but barometric intercept altitudes and minimums can still need CTA correction. Intercept at the applicable corrected intermediate altitude and follow the actual guidance to the corrected DA. For a labeled arithmetic example, if a verified table/system calculation gives a 70-foot DA correction and published DA is 900 feet, use 970 feet or an allowed upward rounding; not 930 feet and not a modified pressure setting. Use actual chart/table values in flight.

AIM 7-3-4: CTA identification and methods · AIM 7-3-5: corrected altitudes, rounding, coordination and geometric-path note · AIM 7-3-1, Table 7-3-1: height/temperature calculation

Fly the missed path while managing the navigator

Brief the complete missed: initial climb and track, turn/altitude restrictions, climb gradient, missed fix/hold and required equipment. Confirm whether the actual navigator suspends sequencing at the MAP, requires acknowledgement/activation or has a different approved procedure. Know how the flight director/autopilot responds to go-around and any navigation source/mode change. No universal “press this button twice” sequence applies to all installations.

At DA without required landing conditions, immediately start the aircraft missed procedure. For an MDA operation, remain above the floor, make the decision at the appropriate point and preserve the MAP path before any early missed turn. Activating the missed does not authorize cutting a turn early or bypassing an altitude gate. Confirm positive climb/performance, source, active leg and actual tracking; use the manufacturer’s configuration/checklist sequence.

If the GNSS source itself is lost, a GPS-coded missed may also be unavailable. Maintain control, use the actual failure procedure and any valid remaining navigation capability, promptly tell ATC what is available, and request assistance/amended routing appropriate to terrain and position. Do not assume Direct To a hold is a safe obstacle-cleared substitute. Rebrief another approach or diversion after reaching a safe workload.

AIM 1-1-17: missed sequencing and GPS familiarization · AIM 5-4-21: missed protection and routing limits · AIM 5-5-5: missed responsibilities · ACS VI.C, printed page 17: aircraft-specific missed preparation

Explore a change in the available operation

Invented study case: a chart offers LPV DA 900 feet, LNAV/VNAV DA 980 feet and LNAV MDA 1,180 feet, with different visibility values. The aircraft is approved for LPV and LNAV/VNAV via WAAS, but it has no approved Baro-VNAV. Before final the receiver announces LNAV. Select a line that the aircraft/service actually supports; do not use the planned LPV DA. If LNAV is usable, rebrief its MDA, stepdowns, visibility, VDP/MAP and missed before beginning final.

Now change one fact: usable LPV service is announced, the chart has a negative-W symbol, and a CTA correction is required. Negative W calls for LNAV/circling minima in flight planning, while actual announced vertical service may be used operationally. Apply the actual CTA corrections to applicable barometric altitudes even on WAAS guidance; the uncompensated Baro range alone does not restrict this geometric path. This example is not alternate-airport planning authority beyond current AIM requirements.

Finally simulate a vertical-only flag late in final. Explain why a conditional LNAV option is not an automatic safe downgrade, especially below its MDA or with unverified stepdowns. State the aircraft failure/missed action and the request for a supported next clearance. Practice these choices with a real chart and actual supplement. This prepares VI.A.S10/S13 and VI.B.S10/S13 minima/visual decisions; no flight performance or immediate DA missed proficiency is demonstrated.

AIM 1-1-18: annunciation, service loss and planning-versus-operation · AIM 5-4-5: negative-W note and line restrictions · AIM 7-3-3–7-3-5: separate temperature requirements · ACS VI.A/VI.B minima and visual-decision skills, printed 14–16

FLIGHT SCENARIO

What would change your plan?