ILS vs RNAV approach explained: compare guidance sources, vertical paths, minima, cockpit setup and when pilots use each.
In aviation and real-world flying, an ILS approach uses runway-based radio transmitters to provide lateral localiser and vertical glideslope guidance. An RNAV approach uses an aircraft’s navigation system, usually GNSS/GPS and an FMS, to follow database waypoints. ILS always supplies a vertical path; RNAV may provide lateral guidance only or both lateral and vertical guidance.
The fundamental difference is the source of the guidance. ILS needles respond to radio signals transmitted near the runway, while RNAV guidance is calculated aboard the aircraft from its position and a coded procedure. RNAV is therefore a family of capabilities rather than one fixed type of approach.
ILS vs RNAV approach at a glance
| Feature | ILS approach | RNAV approach |
|---|---|---|
| Guidance source | Ground-based localiser and glideslope transmitters | Aircraft navigation system using GNSS/GPS or other approved RNAV sensors |
| Lateral guidance | Localiser | Database waypoints and calculated flight-path legs |
| Vertical guidance | Glideslope is part of a full ILS | Depends on the minima: LNAV has none; LNAV/VNAV and LPV provide an approved vertical path |
| Final approach geometry | Normally a straight final aligned with the runway, although some localisers are offset | Can support more flexible transitions and, where authorised, curved or offset segments |
| Cockpit source | VLOC, NAV or equivalent radio-navigation source | GPS or FMS source |
| Typical minima | DA or DH for the full ILS, with the category stated on the chart | MDA for LNAV; DA for LNAV/VNAV or LPV |
| Main dependencies | Serviceable runway transmitters, receiver and protected signal area | Approved equipment, position integrity and a valid procedure database |
How does an ILS approach work?
An ILS provides two separate radio beams: the localiser guides the aircraft left and right, while the glideslope guides it vertically. The paired frequency is tuned or selected automatically, but the crew must still identify the station, set or verify the front course and select the radio-navigation source.
The aircraft should intercept the localiser before reaching the glideslope and normally capture the glideslope from below. Intercepting from above is a common cause of failed capture and can expose the receiver to false glideslope lobes. Pressing the approach button only arms the modes; the flight-mode annunciator must confirm actual LOC and GS capture.
Our practical MSFS 2024 sequence for tuning and capturing an ILS shows how those stages appear in a simulator cockpit.
Is an RNAV approach the same as a GPS approach?
RNAV is the broader navigation concept; GPS is one possible position source. Most RNAV approaches encountered by general-aviation pilots and simmers are GNSS-based, and a chart labelled RNAV (GPS) specifically requires approved GPS capability. Other RNAV operations can combine GNSS, DME/DME and inertial sensors, subject to the procedure and aircraft approval.
RNP is a form of RNAV that adds onboard performance monitoring and alerting. Ordinary RNP approaches should not be confused with RNP AR procedures, which require specific aircraft capability, crew approval and operational authorisation. We explain that distinction in our guide to RNP guidance and approach requirements.
What do LNAV, LNAV/VNAV and LPV mean?
The minima line determines what guidance the pilot may legally use; a magenta path on the display does not by itself prove that vertical guidance is approved.
- LNAV: Lateral guidance only. The pilot observes step-down restrictions and normally descends to an MDA. An advisory glidepath displayed by some avionics does not turn LNAV minima into a vertically guided approach.
- LNAV/VNAV: Approved lateral and vertical guidance, normally flown to a DA. The vertical path may use barometric VNAV or satellite-based augmentation, depending on the installation; temperature restrictions can apply to baro-VNAV.
- LPV: Satellite-based augmentation provides increasingly sensitive lateral guidance and an approved glidepath to a DA. The aircraft, receiver and service availability must support LPV.
- LP: Satellite-based lateral guidance with localiser-like sensitivity but no approved vertical guidance.
The loading, sequencing and source-selection process is covered in our step-by-step method for flying RNAV approaches in Microsoft Flight Simulator.
Is an LPV approach the same as an ILS?
No. LPV can look and feel similar to an ILS because both provide angular lateral guidance and a glidepath, but LPV uses augmented GNSS rather than localiser and glideslope transmitters. An LPV approach remains an RNAV procedure and must be flown using the GPS or FMS navigation source.
ILS is conventionally classified as a precision approach. LPV provides precision-like approach guidance, but its formal classification and approval basis are different. The practical rule is simple: use the minima and equipment requirements printed for the procedure rather than treating LPV as an interchangeable ILS.
Which approach should a pilot choose?
The correct approach is the one cleared or authorised, available for the runway, supported by the aircraft and suitable for the weather. ILS is not automatically better than RNAV, and RNAV is not automatically more modern or more accurate.
- Compare the published minima: An ILS often has low minima at a well-equipped airport, but an LPV can be comparable. The chart decides, not the approach label.
- Check aircraft capability: An ILS receiver cannot fly LPV, while a basic GPS installation may support LNAV but not LNAV/VNAV or LPV.
- Check serviceability: An ILS may be unavailable because of maintenance or a protected-area restriction. An RNAV approach can be affected by integrity warnings, augmentation outages or database problems.
- Consider the arrival geometry: RNAV can provide convenient waypoint transitions where an ILS would require radar vectors, but the loaded transition must match the clearance.
- Plan the missed approach: Confirm that the aircraft can sequence and fly the published missed procedure before starting the approach.
Why will an ILS or RNAV approach not capture in a simulator?
Most failed captures come from the wrong navigation source, unsuitable intercept geometry or unsupported minima rather than a broken autopilot.
| Symptom | Likely cause | Fix |
|---|---|---|
| ILS localiser never captures | GPS/FMS is still selected, or the frequency and front course are wrong | Verify the correct runway ILS, identify it and select VLOC or NAV before intercept |
| Localiser captures but glideslope does not | The aircraft is above the glideslope, the approach is localiser-only, or the glideslope is unavailable | Check the chart and annunciations; intercept an operational glideslope from below |
| RNAV tracks laterally but will not descend | LNAV minima provide no approved vertical path, or VNAV/GP is not supported or armed | Fly the charted step-downs for LNAV or use a supported vertically guided minima line |
| RNAV turns away from final | Wrong transition, a procedure discontinuity or an inappropriate direct-to command | Reload the exact cleared procedure and verify every leg before activating the approach |
A mistake we see constantly is selecting approach mode without checking the flight-mode annunciator. Verify both the active source and the captured modes: VLOC with LOC/GS for ILS, or GPS/FMS with the appropriate lateral and vertical modes for RNAV. If the chart and navigation database disagree, use matching valid data; never improvise a real-world instrument procedure.