What are the types of instrument approaches, and when is each used?

Instrument approaches are used according to the guidance available, aircraft and crew approval, weather, runway and published minima. A 2D approach gives lateral guidance only; a 3D approach adds approved vertical guidance. Common types include ILS, GLS, RNAV/RNP, localiser, LDA, SDF, VOR, NDB and radar approaches.

For readers in our Aviation & Real-World Flying section, the same distinctions apply when practising in a simulator. The chart, supported avionics and active cockpit mode determine what may be flown—not the fact that an approach can be selected from an FMS menu.

Main types of instrument approaches

The most useful way to compare instrument approach types is by the guidance they provide, their normal minima and the circumstances in which they are chosen.

ILS is not automatically preferable to RNAV. The better option is the suitable, serviceable procedure supported by the aircraft and crew, as explained in our comparison of ground-based ILS and FMS/GNSS-based RNAV guidance. Where no ILS is installed or available, consider the practical alternatives available at a non-ILS runway.

2D vs 3D approach: what is the difference?

A 2D instrument approach operation provides approved lateral guidance only, while a 3D instrument approach operation provides approved lateral and vertical guidance.

A calculated continuous-descent path can make a 2D approach more stable, but it remains a 2D operation. For example, an avionics indication such as LNAV+V generally represents advisory vertical guidance; it is not an LNAV/VNAV or LPV approval.

What does lateral guidance mean?

Lateral guidance tells the pilot whether the aircraft is left or right of the required course and how to regain it. It may come from a localiser, GNSS/FMS path, VOR radial, NDB bearing or controller instructions.

Lateral guidance alone provides no authority to follow a generated glidepath or descend early. The pilot must still comply with every published crossing altitude, step-down fix, MDA and missed-approach point. In a simulator, also verify that the CDI or HSI is using the intended source—typically GPS/FMS or VLOC—not merely showing a centred needle from another source.

Are precision, APV and non-precision approaches the same as 2D and 3D?

The terms overlap, but they are not exact synonyms under every regulatory system. A non-precision approach normally corresponds to a 2D operation. A precision approach is 3D, but a 3D approach is not necessarily classed as precision.

• Non-precision approach: approved lateral guidance without approved vertical guidance, such as VOR, LOC or RNAV LNAV.
• Approach with vertical guidance (APV): approved lateral and vertical guidance that was not placed in the legacy precision category, commonly LPV or LNAV/VNAV.
• Precision approach: approved lateral and vertical precision guidance, such as ILS, GLS, MLS or PAR where published and authorised.

ICAO material may also describe Type A and Type B instrument approach operations. Type A has a minimum height at or above 250 feet; Type B has a decision height below 250 feet. These labels classify the operation and minima rather than naming the navigation system.

What do instrument approach categories A, B, C and D mean?

Aircraft approach categories determine which minima row and protected area apply based on the aircraft's defined approach speed. They are unrelated to the A/B distinction for ICAO Type A and Type B operations.

The governing authority and aircraft documentation define the speed calculation to use. If the approach is flown faster than the upper limit for its normal category, higher-category minima or restrictions may apply.

ILS CAT I, CAT II and CAT III mean something different again. They describe progressively lower-visibility precision operations and the facilities, aircraft systems, crew qualifications and approvals needed to conduct them; they do not describe aircraft speed.

What do LNAV, LP, LNAV/VNAV and LPV mean on an RNAV approach?

The minima line supported by the active avionics mode determines how an RNAV approach may be flown; the RNAV or RNP title alone does not.

• LNAV: basic approved lateral guidance, normally with an MDA. A displayed advisory path does not alter the LNAV minima.
• LP: more angular and sensitive SBAS lateral guidance than LNAV, but no approved vertical guidance. It is normally flown to an MDA.
• LNAV/VNAV: approved lateral and vertical guidance flown to a DA. Vertical guidance may come from approved Baro-VNAV or another authorised system, depending on the installation and procedure.
• LPV: SBAS-supported lateral and vertical guidance flown to a DA. It can feel like ILS in the cockpit, but it does not use an ILS localiser or glideslope transmitter.

LPV is not simply LP with an advisory glidepath. It is a distinct, approved minima capability. If the avionics downgrade from LPV or LNAV/VNAV, the pilot must use a minima line and procedure permitted by the resulting annunciation, or discontinue the approach when the approved procedure requires it.

RNP adds onboard performance monitoring and alerting to area navigation. Standard RNP approach capability does not by itself authorise an RNP AR procedure, where AR means Authorisation Required.

What Baro-VNAV equipment does an RNP AR approach require?

For RNP AR operations requiring barometric vertical navigation, the approved Baro-VNAV system must be integrated with a flight director and/or autopilot as specified by the aircraft and operational approval. The installation also requires the applicable RNP performance-monitoring and alerting capability.

The correct local altimeter setting and any charted temperature limits are critical because Baro-VNAV derives its vertical path from barometric information. Some approved installations provide temperature compensation, but its presence must not be assumed. Loading an RNP AR procedure into a simulator or FMS does not demonstrate that the aircraft configuration, crew or operator is authorised to fly it.

LDA vs SDF: what is the difference?

An LDA normally provides localiser-like accuracy on a course that may be offset from the runway, while an SDF provides a wider and less precise lateral course. Both names are associated particularly with United States procedure terminology.

Neither should be treated as a full ILS unless the procedure explicitly supplies and authorises the required vertical guidance. Follow the charted final course and minima rather than aligning visually with the runway too early. A back course must not be inferred merely because a signal can be received; it must be a published procedure.

How is an instrument approach selected in practice?

The selected approach must be suitable for the runway and conditions, available, supported by the aircraft, and legal for the crew or operator to fly. ATC may assign an approach, but the pilot remains responsible for accepting it or reporting unable.

1. Choose a usable runway. Check wind, runway condition, landing distance and operational restrictions. The approach with the lowest minima is not useful if it leads to an unacceptable tailwind or insufficient runway.
2. Compare weather with the correct minima. Use the minima row for the aircraft category and the guidance the aircraft can actually provide. Include applicable visibility and approach-ban rules.
3. Confirm eligibility. Check required navigation equipment, aircraft approval, crew qualification, navigation-database validity and any special authorisation. An installed GPS does not authorise every RNAV or RNP procedure.
4. Check serviceability and restrictions. Review navigation-aid status, satellite or augmentation availability, required altimeter sources, temperature limits and relevant operational notices.
5. Cross-check the loaded procedure against the chart. Verify the runway suffix, transition, fixes, final course, altitude constraints, minima and missed approach. Simulator navigation data and chart revisions may not match.
6. Brief the mode changes and failure plan. Decide which lateral and vertical modes should be armed or active, where capture is expected, and what will trigger an immediate missed approach.

For practical cockpit execution, our step-by-step simulator approach workflow covers loading, briefing, intercepting and monitoring the procedure.

How do DA, MDA and circling minima affect the approach?

A decision altitude or height (DA/DH) is normally used for a 3D approach. If the required visual reference is not established at DA, the missed approach is initiated; DA is not a level-off altitude.

A minimum descent altitude or height (MDA/MDH) is normally used for a 2D approach. The aircraft must not descend below it without the required visual reference and must start the missed approach no later than the applicable missed-approach point. A continuous-descent final approach may avoid levelling at MDA, but it does not cancel any published altitude.

Circling is a visual manoeuvre conducted after an instrument approach, usually to land on another runway or when straight-in alignment is unsuitable. The aircraft must remain within the protected circling area and at or above circling MDA until a normal landing descent can be made.

Published altitude and visibility limits both matter. Our guide to DA, MDA and visibility minima in a simulator explains how to identify the applicable figures and decide whether the approach may continue.

Are visual and contact approaches instrument approaches?

Visual and contact approaches can be conducted while operating under IFR, but they are not instrument approach procedures in the same sense as ILS, RNAV or VOR. They depend on specified visual conditions and references, and contact approaches are available only under authorities and circumstances that permit them.

Common approach-selection and simulator errors

The mistake we see most often is treating every magenta or green glidepath as approved vertical guidance. Several other errors produce convincing cockpit indications while putting the aircraft on the wrong procedure or below a protected altitude.

• Wrong navigation source: the approach is loaded in the FMS, but the CDI remains on VLOC—or an ILS is expected to capture while the display remains on GPS. Confirm the required source and annunciation before final intercept.
• Incorrect ILS setup: verify the frequency, identifier and front course. Intercept the glideslope from below at the charted altitude rather than descending onto it from above.
• Advisory path mistaken for approval: on LNAV, LP, LOC, VOR or NDB minima, comply with published altitudes and MDA even if the avionics draw a smooth descent path.
• Wrong RNAV minima after a downgrade: use only the minima supported by the active approach mode and approved equipment. Do not continue on LPV minima after an LNAV downgrade.
• Incorrect altimeter data: a wrong setting, remote source used contrary to a chart note, or ignored temperature restriction can invalidate Baro-VNAV guidance and obstacle clearance assumptions.
• Procedure and database mismatch: compare every fix and altitude with the chart. If the simulator's navigation cycle differs, do not repair the route by inventing constraints.
• RNP AR treated as ordinary RNAV: curved legs on the display do not prove that the add-on models the required containment, monitoring, alerting or vertical guidance.
• No missed-approach plan: brief the initial altitude, track and mode changes before reaching final. Guidance loss, an unstable approach or missing visual reference should lead to the published missed approach, not improvised manoeuvring.