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Instrument Approaches & IFR Procedures

ILS CAT I / II / III

Decision heights, RVR and visibility, aircraft equipment and approval, ground equipment, crew and operator authorisation and the CAT III subcategories.

  • Category minima
  • Equipment and approval requirements
  • CAT III subcategories
STAGEview from the cockpit at the DA / DH with the RVR set · side view of the glide path and the ground in view

Loading the tool…

CONTROLSoperation · DA / DH · RVR · runway and ground equipment · aircraft · crew and operator
READOUTlive · minimums, what is in sight, the rule, continue or missed approach, what is missing
HOW TO USEquick guide

Pick an operation — CAT I, SA CAT I, CAT II, SA CAT II, or CAT III with a fail-passive or a fail-operational landing system — and set the reported RVR. The top view is what you would see from the cockpit at that height: only the lights and markings inside the visual range are drawn. The side view shows the glide path, the DA or DH (or the alert height), the aircraft and, in green, the stretch of ground in view. Drag the aircraft down the glide path to watch more of the runway appear.

At the DA or DH the readout says whether you may continue and why. CAT I and SA CAT I use the ten references of 14 CFR 91.175 (c); CAT II under part 91 uses the six of 91.189 (d); a fail-passive CAT III landing needs the touchdown zone in sight; a fail-operational system with an alert height needs no visual reference at all. The approach lights alone take you down to 100 ft above the touchdown zone — no lower unless the red terminating or red side row bars (or another reference) are in sight.

Lower minimums need more than a lower DH: the runway, the ILS, the RVR sensors, the aircraft and the crew all have to qualify. Switch lights off, take away the radio altimeter or the second pilot, change the ILS classification, and "What is missing?" lists every element the operation still needs, with its source, and names the lowest operation the set-up supports. Practice gives eight approaches: continue or go around?

Assumption: schematic airport, lights and markings drawn after the AIM figures — never a real procedure, never for navigation. 3.00° glide path, 55 ft threshold crossing height, 150 ft wide runway, aircraft exactly on the localizer and glide slope; the reported touchdown RVR is treated as the visual range from the cockpit, and the window shows the ground up to 20° below the horizon (a model value; real cockpit cut-off angles depend on the aircraft); flat terrain under the approach. The decision shown is the regulatory picture only — your authorization (OpSpecs, MSpecs or letter of authorization), the AFM and the chart govern.

SOURCES & METHODformulas · references

Minimums (lowest values; a published, pilot or equipment minimum that is higher governs, 14 CFR 91.175 (b), 91.189 (c)): CAT I DA 200 ft and RVR 1800 (RVR 2400 without touchdown zone and centreline lights unless a flight director, autopilot or HUD is used to the DA; Order 8400.13F ch. 2 and the TPP Inoperative Components table, which also raises the minimum to RVR 4000 with the approach lights out and to 1/2 mile with the RVR out); SA CAT I DH 150 ft on the radio altimeter, RVR 1400 (HAT 150–170) or 1600 (171–185) (8400.13F table 3-1); CAT II DH 100 ft, RVR 1200 (1600 without a rollout sensor; 1000 with autoland or HUD to touchdown, 8400.13F ch. 4 and 6; AC 120-118 table 3-2); SA CAT II DH 100 ft, RVR 1200 with autoland or HUD to touchdown on runways without touchdown zone or centreline lights (8400.13F ch. 5); CAT III by AC 120-118 table 3-3: fail-passive or fail-operational without a rollout system 600 / 600 / 300 (touchdown / mid / rollout RVR, with a DH — 50 ft is the lowest the AC ties to RVR 600), fail-passive with a rollout system 600 / 400 / 300, fail-operational with a fail-passive rollout 400 / 400 / 300, fail-operational with a fail-operational rollout 300 / 300 / 300 (no DH; an alert height at or below 200 ft, typically not below 50 ft); the ILS classification III/D/3 limits CAT III to RVR 700, III/E/3 to 600, III/E/4 allows 300 (8400.13F 7-4 a). RVR is converted to visibility only for CAT I (91.175 (h); AIM 5-4-20 a: use the next higher RVR value).

Requirements checked (each with its source on the page): ground — approach lights (ALSF-2 for standard CAT II and III; SSALR, MALSR or ALSF for CAT I RVR 1800 with reduced lighting, SA CAT I and SA CAT II), high intensity runway lights, touchdown zone and centreline lights, RVR sensors (touchdown always; rollout for CAT II below 1600, midpoint on runways over 8,000 ft; touchdown, midpoint and rollout for CAT III), ILS performance classification (II/D/2 for CAT II and SA CAT II, III/D/3 or better for CAT III), an operating control tower, a grooved runway for CAT III, landing distance (5,000 ft SA CAT I, 6,000 ft SA CAT II); aircraft — two ILS receivers, radio altimeter, rain removal, the flight guidance the operation needs (HUD to DH or a CAT II autopilot for SA CAT I; HUD, autopilot coupled to DH or autoland for CAT II, AC 120-118 3-3 a (5); autoland or HUD to touchdown for SA CAT II and CAT III), the part 91 appendix A equipment; crew — part 91: a pilot in command and a second in command (91.189 (a)), the 61.67 / 61.68 pilot authorization, a letter of authorization and the CAT II / III manual (91.191); certificate holders: OpSpecs / MSpecs C060 (91.189 (g)); SA CAT I is prohibited for single-pilot operations.

Publications differ on CAT III. The Pilot/Controller Glossary still defines CAT IIIA (no DH, RVR not less than 700 ft), IIIB (RVR not less than 150 ft) and IIIC (no RVR minimum); the 2017 Instrument Procedures Handbook adds a DH below 100 / 50 ft and notes that no U.S. operator has been approved for CAT IIIc; AC 120-118 (2018) says the FAA removed the IIIa / IIIb / IIIc definitions in 2011, describes CAT III by fail-passive and fail-operational systems, and gives RVR 300 for touchdown, mid and rollout as the lowest minimums for U.S. operators (its appendix quotes the ICAO definitions, with RVR 600 / 200 ft boundaries). This page follows AC 120-118 and Order 8400.13F and shows the older names only for comparison. The glide path and the ILS needles are the same calculation as the IFR Trainer's ILS module (identical results checked), measured from the glide path intercept point.

  1. 14 CFR 91.175 (b), (c) (1)–(3), (h) (eCFR current, read 2026-10-15): authorized DA/DH, operation below DA/DH, the ten visual references and the 100 ft rule for the approach lights, comparable values of RVR and visibility; 14 CFR 1.1 (Category II and Category III operations, DA, DH)
  2. 14 CFR 91.189 (a)–(g) (crew of two with authorizations, ground and airborne components operating, authorized DH, the six visual references, CAT III without DH by letter of authorization, certificate holders by OpSpecs / MSpecs), 91.191 (CAT II / III manual), part 91 appendix A (CAT II instruments and equipment), 61.67 and 61.68 (CAT II / CAT III pilot authorizations)
  3. FAA Order 8400.13F with Change 1 (Active; change effective 18 Aug 2022), ch. 1–7: CAT I RVR 1800 with reduced lighting, SA CAT I (table 3-1), standard CAT II, SA CAT II, CAT II RVR 1000, standard CAT III (performance classifications II/D/2, III/D/3, III/E/3, III/E/4; lighting, RVR sensors, control tower, landing distance)
  4. FAA Advisory Circular 120-118 (2 July 2018, Active), Criteria for Approval/Authorization of All Weather Operations: 1-1 (nomenclature: CAT IIIa / IIIb / IIIc removed in 2011), 3-3, 3-6, 3-7 (SA CAT I, SA CAT II, CAT II RVR 1000, table 3-2, visual references), 3-8 (alert height, fail-passive and fail-operational systems, table 3-3), appendix 1 definitions, appendix 3 sample OpSpec C060
  5. Pilot/Controller Glossary (current), ILS CATEGORIES; FAA Instrument Procedures Handbook, FAA-H-8083-16B (2017), ch. 4 ILS approach categories and Figure 4-41 (the older CAT IIIa / IIIb / IIIc wording, shown for comparison)
  6. U.S. Terminal Procedures Publication front matter, cycle 2610 (1–29 Oct 2026): Inoperative Components or Visual Aids Table; Aeronautical Information Manual (effective 9 July 2026), 2-1-1 and FIG 2-1-1 (approach light systems), 2-1-4 (runway edge lights), 2-1-5 (centreline and touchdown zone lights), 5-4-20 a (RVR conversion)
  7. Cross-tool: the glide path height and the ILS needles are the same calculation as the IFR Trainer's ILS module, identical results checked; the PAPI picture is the Visual Descent Point Challenge's
  8. Model choices of this tool (stated on the page): schematic airport, lights and markings; 3.00° glide path, 55 ft TCH, 150 ft runway; aircraft on the localizer and glide slope; reported touchdown RVR treated as the visual range from the cockpit; window down to 20° below the horizon; flat terrain; the alert height is an aircraft-specific example
Sources & accuracyAuthority: FAALast checked: 2026-10-18Pilot-reviewed: not yetReport an error