Learn the types of instrument approaches—ILS, RNAV, RNP, VOR and more—and when each is used, including guidance, minima and common traps.
In real-world aviation, instrument approaches fall into three practical groups: precision approaches, approaches with vertical guidance, and non-precision approaches. Pilots use the procedure authorised for the aircraft and crew that best suits the runway, available navigation equipment, weather and serviceability; the published minima determine how low they may descend.
Terminology differs between regulators. A 3D instrument approach operation provides approved lateral and vertical guidance, while a 2D operation provides lateral guidance only. The familiar precision, approach with vertical guidance (APV) and non-precision groupings remain useful, although they are not exact synonyms for every ICAO or national classification.
Main types of instrument approaches
The following grouping connects each approach name with its guidance, normal use and principal limitation.
| Approach type | Guidance | When it is used | Main limitation |
|---|---|---|---|
| ILS | Ground-based localiser and glideslope | For a stabilised straight-in approach, particularly in low cloud or visibility. CAT II and CAT III operations support lower visibility where fully approved. | Requires a serviceable runway installation and compatible aircraft. Lower categories also require qualified crews, aircraft and airport facilities. |
| GLS | GBAS-corrected satellite lateral and vertical guidance | Provides an ILS-like precision approach at suitably equipped airports. | Both the airport and aircraft must support the published GLS service. |
| LPV or LNAV/VNAV | Approved RNAV lateral and vertical guidance | Used for a continuous descent to a decision altitude, often at runways without an ILS. | The available minima depend on the receiver, satellite augmentation or barometric VNAV capability, and chart notes. |
| RNP AR | FMS path with onboard performance monitoring, often including curved RF legs | Used where terrain, airspace or runway alignment requires a tightly contained flight path. | Requires specified aircraft capability, crew training and operator or regulatory authorisation. |
| RNAV LNAV or LP | Approved lateral guidance only | Used for GPS/RNAV approaches when approved vertical guidance is unavailable. | Normally uses an MDA. A displayed advisory glidepath does not change the approach into a vertically guided procedure. |
| LOC, LDA or SDF | Localiser-type lateral guidance | Used when only lateral ground guidance is published, including some offset approaches. A localiser-only procedure may remain available when an ILS glideslope is unavailable. | No approved glideslope; minima are generally higher than for the full ILS. |
| VOR or NDB | Ground-beacon course or bearing guidance | Used where these conventional procedures remain published, including some remote airports and backup operations. | No approved vertical guidance, with accuracy and minima affected by aid geometry and procedure design. |
| PAR or ASR | Controller-issued radar instructions | Used at aerodromes providing surveillance approaches, commonly in military, training or contingency operations. | PAR supplies precision azimuth and elevation guidance; ASR normally provides lateral guidance without an approved glidepath. |
Our operational comparison of ILS and RNAV guidance explains why neither family is automatically the better choice. For conventional-navigation practice, simmers can also practise VOR and NDB tuning and tracking before attempting an associated approach.
What do LNAV, LPV and LNAV/VNAV mean?
The RNAV approach title alone does not identify the guidance a pilot may use; the applicable minima line does. The principal options are:
- LPV: SBAS-supported lateral and vertical guidance flown to a decision altitude. It behaves much like an ILS in the cockpit but is commonly classified as APV rather than a precision approach.
- LNAV/VNAV: approved lateral and vertical guidance using suitable satellite or barometric VNAV equipment. Baro-VNAV procedures can carry temperature, altimeter-source and equipment restrictions.
- LP: enhanced SBAS lateral guidance without approved vertical guidance, normally flown to an MDA.
- LNAV: lateral guidance only, also normally flown to an MDA. Any generated vertical path may be advisory unless the chart and aircraft approval say otherwise.
Our simulator walkthrough of LNAV, LP and LPV approach modes covers how these differences appear in the cockpit. RNP AR is a separate concern: the ability to load the procedure does not prove that the aircraft or operator is authorised to fly it. We cover the FMS workflow and performance monitoring in our guide to loading and monitoring an RNP procedure in a flight simulator.
How is an instrument approach selected in practice?
Pilots select or accept an approach only after checking that it is suitable, available and legal for the planned landing. ATC may assign the procedure, but the pilot must request an alternative or report unable when the aircraft, crew or conditions do not meet its requirements.
- Check the runway and conditions. Consider wind, visibility, cloud, runway state, landing distance and operational restrictions. The approach with the lowest minima may lead to an unsuitable runway.
- Confirm aircraft and crew eligibility. Check the required navigation equipment, aircraft documentation, database validity and any operator or regulatory approval. An installed GPS does not automatically authorise every RNAV or RNP procedure.
- Verify serviceability. Review relevant notices, navigation-aid status, satellite-availability requirements, altimeter sources and temperature limitations.
- Compare the published minima. Use the correct aircraft category and the minima line supported by the equipment and annunciated approach mode. Required visibility and approach-ban rules also depend on the governing authority.
- Brief and cross-check the procedure. Verify the runway, transition, final approach course, altitude constraints, minima and missed-approach instructions against the chart rather than trusting the loaded route unquestioningly.
How do DA, MDA and circling minima affect the approach?
Decision altitude and minimum descent altitude define different actions at the bottom of an approach. Precision and APV procedures normally use a DA/DH: if the required visual reference is not established, the pilot initiates the missed approach rather than levelling at DA.
A 2D approach normally uses an MDA/MDH and a missed-approach point. The aircraft must not descend below MDA without the required visual reference. A continuous-descent final approach can improve stability, but a calculated or advisory descent path is not permission to descend below a published altitude.
Circling is not a separate navigation system. It is a visual manoeuvre following an instrument procedure, used when landing on another runway or when the final approach is not aligned for a straight-in landing. The aircraft must remain within the protected circling area and at or above circling MDA until a normal descent can be made.
Aircraft approach categories such as A, B, C and D determine the applicable minima row and protected area based on approach-speed criteria. They are unrelated to ILS CAT I, II and III, which describe low-visibility precision operations and their associated approvals.
Are visual and contact approaches instrument approaches?
Visual and contact approaches may be conducted while operating under IFR, but they are not instrument approach procedures in the same sense as ILS, RNAV or VOR approaches. They rely on specified visual conditions and references, and a contact approach is available only under the rules of authorities that permit it.
Common approach-selection and flying errors
A mistake we see constantly in simulators—and one that matters in real operations—is treating every displayed glidepath as authorised vertical guidance. Other frequent errors include:
- Choosing LPV minima when the avionics have downgraded to LNAV, or using an LNAV/VNAV line without the required equipment.
- Descending below an MDA because an advisory VNAV path looks centred.
- Flying an ILS with the wrong navigation source, frequency or front course, or attempting to intercept the glideslope from above instead of joining it from below at the published altitude.
- Loading the correct approach but the wrong transition, runway suffix or missed-approach procedure.
- Ignoring a navigation-aid outage, temperature restriction, altimeter note or loss of required navigation-performance monitoring.
- Continuing after the approach becomes unstable or required guidance is lost instead of applying the published missed-approach procedure or an authorised alternative.