Approach & Landing
ILS, VOR, RNAV/GPS, and visual approach procedures — decision heights, minimums, and missed approach guidance.
An instrument approach procedure (IAP) is a series of predetermined manoeuvres for the orderly transfer of an aircraft under IFR from the beginning of the initial approach to a landing, or to a point from which a landing may be made visually. Approaches are classified as Precision, APV (Approach with Vertical Guidance), or Non-Precision.
Approach Categories
Precision Approach
Provides lateral AND vertical guidance to minimums. ILS (CAT I/II/III), MLS, GLS (GBAS).
Decision Height (DH)APV (Approach with Vertical Guidance)
Provides lateral and vertical guidance but does not meet ICAO precision approach standards. LPV, LNAV/VNAV, RNP AR.
Decision Altitude (DA)Non-Precision Approach
Provides lateral guidance only. VOR, NDB, LOC, LNAV. Pilot manages own vertical profile.
Minimum Descent Altitude (MDA)The key distinction between DA/DH and MDA is critical: at a DA/DH you must have required visual references before descending below — the aircraft continues descending during the decision. At an MDA you level off and continue to the missed approach point (MAP) — you may not descend below the MDA unless the required visual references are established.
ILS — Instrument Landing System
The ILS is the most common precision approach aid worldwide. It provides two radio beams — the localiser (lateral guidance) and the glide slope (vertical guidance, typically 3°) — along with marker beacons or DME to provide distance/position awareness along the approach.
ILS Components
| Component | Frequency | Function | Notes |
|---|---|---|---|
| Localiser (LOC) | 108.10–111.95 MHz | Lateral guidance along the runway centreline | ±2.5° full-scale deflection; paired with glide slope frequency automatically |
| Glide Slope (GS) | 329.15–335.00 MHz (UHF) | Vertical guidance along the glide path | Typically 3° glide angle (2.5°–3.5° permitted under ICAO); ±0.7° full-scale deflection |
| Outer Marker (OM) | 75 MHz | Position fix approximately 4–7 nm from the threshold | Blue cockpit light; audio: two dashes per second (— —); often replaced by DME fix |
| Middle Marker (MM) | 75 MHz | Alerts crew approaching DH / CAT I minima region | Amber cockpit light; audio: alternating dot-dash (·–·–); approximately 0.5–1 nm from threshold |
| Inner Marker (IM) | 75 MHz | Position fix for CAT II/III operations | White cockpit light; audio: continuous dots (·····); close to the threshold |
| DME | Paired with ILS LOC | Distance to touchdown — replaces or supplements markers | Referenced as DME ILS or collocated DME; distance 0 typically at threshold |
ILS Categories
| Category | Decision Height (DH) | RVR Minima | Notes |
|---|---|---|---|
| CAT I | ≥200 ft above TDZ elevation | RVR ≥550 m (or visibility ≥800 m) | Standard for most certified ILS approaches; no special crew or aircraft approval beyond basic IR |
| CAT II | 100–199 ft above TDZ elevation | RVR 300–549 m | Requires CAT II approved aircraft, crew training, and aerodrome CAT II infrastructure |
| CAT IIIA | <100 ft above TDZ (or no DH) | RVR ≥200 m | Requires autoland or equivalent; fail-operational or fail-passive systems; full aerodrome CAT III lighting |
| CAT IIIB | <50 ft above TDZ (or no DH) | RVR 50–199 m | Advanced autoland with rollout guidance; fail-operational to touchdown and rollout required |
| CAT IIIC | No DH | No RVR limit (zero visibility) | Full blind landing and taxi — not mandated anywhere as of ICAO publication; requires full taxiway guidance systems |
CAT II and III operations require special crew training, aircraft certification, and aerodrome infrastructure approval. Never attempt CAT II/III operations without appropriate qualifications, currency, and aircraft equipment certification for the specific category.
VOR Approach
A VOR approach uses a VOR station for lateral guidance. The aircraft tracks inbound on a specific VOR radial to the runway or to a point from which the runway is in sight. No vertical guidance is provided — the pilot uses the published step-down altitude profile or a constant descent angle (CDA) technique.
- Final approach course is a specific inbound radial (e.g. "VOR Runway 27 via radial 090 inbound")
- The missed approach point (MAP) is typically overhead the VOR or at a published DME fix
- Aircraft levels off at the Minimum Descent Altitude (MDA) and continues visually to the MAP
- If the required visual reference is not established at the MAP — the missed approach must be executed immediately; no further descent is permitted below MDA
- Typical minima: 400–600 ft above field elevation + visibility (varies widely by procedure design)
- VOR approaches are being phased out in favour of RNAV/GNSS procedures at many aerodromes
RNAV / GPS Approaches
Area Navigation (RNAV) approaches use GNSS (GPS) as the primary sensor, with or without augmentation. Different procedure types offer varying levels of accuracy and vertical guidance.
LNAV — Lateral Navigation
Non-precision approach using GPS for lateral guidance only. No vertical guidance signal — the pilot manages the descent profile using published step-down fixes. Minimums expressed as MDA, typically 250–400 ft above TDZ. The lowest common RNAV approach type; available on basic IFR GPS receivers.
LP — Localiser Performance
Uses SBAS (WAAS or EGNOS) to provide precision GPS lateral guidance with accuracy equivalent to an ILS localiser. No vertical guidance. Expressed as MDA. More accurate laterally than standard LNAV; useful where glide path cannot be coded.
LNAV/VNAV — Lateral Navigation / Vertical Navigation
GPS lateral guidance combined with baro-VNAV (barometric vertical navigation from the FMS) to provide a continuous descent profile. Expressed as DA, typically 250–350 ft above TDZ. Requires a baro-VNAV capable FMS; accuracy affected by cold temperature (apply temperature corrections as published).
LPV — Localiser Performance with Vertical Guidance
Uses SBAS (WAAS in North America, EGNOS in Europe) to provide both precision lateral and vertical guidance. Minimums as low as 200 ft DA — functionally equivalent to ILS CAT I. The most accurate GPS approach type widely available. Requires an SBAS-capable GPS/FMS; vertical guidance is independent of barometric altimeter errors.
RNP AR — Required Navigation Performance (Authorisation Required)
High-accuracy curved approaches designed for airports with significant terrain, obstacles, or airspace constraints. Can fly curved final approach segments using RF (radius-to-fix) legs. Requires specific RNP AR approval for both the aircraft (avionics certification) and the flight crew (training and currency). Minimum navigation performance may be as low as RNP 0.1 nm on final.
SBAS Coverage: LPV approaches require an active SBAS signal (WAAS/EGNOS). Always check NOTAMs for GNSS/SBAS outages before planning RNAV approaches, especially in areas of known solar activity or ground interference. LNAV remains available as a fallback if SBAS is unavailable.
Visual Approach and Circling
Visual Approach
A visual approach is approved by ATC when the pilot has the aerodrome environment in sight and can maintain own terrain and obstacle separation. It still requires an ATC clearance. Once visual, the pilot is responsible for terrain and obstacle clearance. Standard instrument departure and missed approach procedures may not apply — pilots must plan the go-around from a visual approach carefully.
Circling Approach
Used when the instrument approach runway differs from the intended landing runway — for example, when the ILS serves runway 10 but the active landing runway is 28. The aircraft flies the instrument approach to MDA, then manoeuvres visually to align with the landing runway. The circling area is protected based on aircraft performance category.
| Aircraft Category | Maximum Speed (Vat) | Circling Radius |
|---|---|---|
| A | ≤100 kt | 1.68 nm |
| B | 101–135 kt | 2.66 nm |
| C | 136–180 kt | 4.20 nm |
| D | 181–205 kt | 5.28 nm |
| E | 206–240 kt | 6.94 nm |
Aircraft performance categories (A–E) are based on 1.3 × Vso (stall speed in the landing configuration) at maximum certificated landing weight. Never exceed the category speed during circling — doing so takes the aircraft outside the protected area.
Circling in IMC: If visual contact is lost during circling, execute the missed approach immediately. Begin the turn toward the runway that the instrument approach was flown, climb to the missed approach altitude, then proceed as published. Losing visual reference during circling is a high-risk situation.
Missed Approach
The missed approach (go-around) must be executed immediately when any of the following occur:
- Required visual reference is not established at DA/DH (precision / APV) or at the MAP (non-precision)
- Visual reference is lost after DA/DH or below MDA
- ATC instructs a go-around at any point
- A safe landing cannot be assured (runway incursion, wind shear, unstabilised approach)
Do not delay. Execute the published missed approach procedure immediately — do not attempt to salvage the approach.
The published missed approach procedure specifies:
- The initial climb gradient required (e.g. 2.5%) — must be achievable in the go-around configuration
- Turning point(s) — defined by a fix, altitude, or distance
- The holding fix and holding pattern altitude
- ATC may issue a different missed approach clearance — always comply unless safety demands otherwise
Stabilised Approach Criteria
Industry standard (IATA, IFALPA, Flight Safety Foundation) requires all approaches to be stabilised by 1000 ft AAL in IMC and 500 ft AAL in VMC. All parameters must be met and maintained from the stabilisation gate to touchdown.
| Parameter | Requirement |
|---|---|
| On centreline | ≤½ dot localiser / LPV deflection; or within ±5° of runway centreline on visual approach |
| On glide path | ≤1 dot glide slope deflection; or within PAPI guidance (2 red / 2 white = on glidepath) |
| Speed | Within Vref ±10 knots (or as specified in the Operations Manual / FCOM) |
| Rate of descent | ≤1000 fpm (≤1500 fpm only in exceptional, operationally justified circumstances) |
| Configuration | Aircraft in the correct landing configuration — gear down, flap/slat at landing setting |
| Power | Appropriate power set for the approach — not idle; power changes should be small and controlled |
| Checklist | Landing checklist complete and verified by the time of the stabilisation gate |
If any stabilised approach criterion is not met at the applicable gate, a go-around must be initiated without delay. Continued unstabilised approaches are a leading cause of runway excursions and Controlled Flight Into Terrain (CFIT) accidents. Airline Operations Manuals treat the go-around decision as mandatory — not discretionary — when the criteria are not met.