Low Visibility Operations

Low visibility operations (LVO) are the take-offs and approaches flown when fog, low cloud or heavy precipitation push the runway visual range (RVR) or the decision height (DH) below what a standard Category I operation allows. They rest on a chain of four links: an aircraft certified for the operation, a crew trained and current in it, an operator approved to conduct it, and an aerodrome whose guidance, lighting and procedures protect it. If any link is missing, the lower minima are not available.

Europe rewrote its all-weather operations rules through Regulation (EU) 2021/2237, which amended the Air Operations Regulation (EU) No 965/2012 and applied from 30 October 2022. The terms now follow ICAO. Textbooks and question banks still carry the older EU-OPS vocabulary, so this article gives the current EASA framework, flags the old terms, and sets out where the FAA differs. For the ground equipment itself, see the instrument landing system.

What are low visibility operations

EASA defines low visibility operations as approach or take-off operations on a runway with an RVR below 550 m or with a DH below 200 ft (EASA writes "low-visibility"). Instrument approach operations are classified by their lowest minima:

• A Type A operation has a minimum descent height or DH at or above 250 ft.
• A Type B operation has a DH below 250 ft and is subdivided into CAT I, CAT II and CAT III.

Where the DH and the RVR fall into different categories, ICAO's note says the operation is conducted to the requirements of the more demanding one. Each operator establishes its aerodrome operating minima under CAT.OP.MPA.110 (see aerodrome operating minima). Take-offs below 400 m RVR, CAT II and CAT III approaches, and operations with operational credits also need a specific approval under Part-SPA, Subpart LVO (SPA.LVO).

Low visibility procedures (LVP)

Low visibility procedures (LVP) are the measures an aerodrome applies to keep low visibility operations safe. An aerodrome that offers CAT II or CAT III approaches or low visibility take-offs publishes its own procedures and triggers, usually with a preparation phase as the RVR or cloud base falls and full LVP at published thresholds. ICAO's European guidance on all weather operations at aerodromes (EUR Doc 013) describes the elements. Crews normally learn from the ATIS that "LVP are in force". Typical measures are:

• Protection of the ILS critical and sensitive areas, so aircraft hold at CAT II/III holding positions further from the runway.
• Greater spacing between arrivals, so that the preceding aircraft has cleared the sensitive area before the next one is close in.
• Restrictions on vehicles and people on the manoeuvring area, with stop bars in use.
• Monitoring of the ILS, lighting and RVR systems, with standby power ready.

CAT II and CAT III minima depend on these protections, so they are not available unless LVP are in force. The cost is capacity, with holding and delays that the fuel plan must allow for.

Low visibility take-off (LVTO)

Under the 2022 rules, a low visibility take-off (LVTO) is a take-off in an RVR below 550 m. Take-offs between 550 m and 400 m need no specific approval, but the minima still depend on the runway lighting. Below 400 m, the operator needs an LVTO approval under SPA.LVO.

EASA's AMC sets the conditions for the lowest values. Below 150 m, and down to 125 m, the runway must have high-intensity centreline lights no more than 15 m apart and high-intensity edge lights no more than 60 m apart. LVP must be in force, and a 90 m visual segment must be available from the flight deck at the start of the take-off run. The required RVR must be met at every reporting point relevant to the take-off run. Below 125 m the flight manual minimum applies, never lower than 75 m, together with further aircraft and runway requirements.

A 90 m segment at 15 m spacing shows six intervals, or seven centreline lights, enough to track the centreline by eye. A take-off alternate may be required when the weather at the departure aerodrome is below landing minima.

CAT II and CAT III approaches

A CAT II or CAT III approach needs all four links of the chain:

• Aircraft: certified for the category under CS-AWO or equivalent, with its capability stated in the flight manual. The DH is read from the radio altimeter.
• Crew: two pilots, both trained and qualified for the operation and current in it.
• Aerodrome: a suitable ILS or equivalent approach system, lighting that includes touchdown zone and runway centreline lights, and LVP in force.
• Operator: a SPA.LVO approval, with procedures, training and records.

At the DH the pilot needs the required visual reference, a segment of lights long enough to confirm position and trend. With a fail-operational system and no DH, the landing does not depend on seeing the runway before touchdown. The touchdown zone RVR is controlling. Lowest minima generally rely on autoland or a head-up guidance system to touchdown.

The minimum equipment list (MEL) states which items may be inoperative for dispatch. Many entries carry MEL operational and maintenance procedures, marked (O) and (M), which must be completed before the aircraft flies. Separately, the flight manual lists the equipment each landing category needs, so an aircraft dispatched with items inoperative may be downgraded, for example from fail-operational to fail-passive, or to CAT II or CAT I only. The crew checks the landing capability against the forecast before departure and again before the approach.

SA CAT I and SA CAT II (formerly LTS CAT I and OTS CAT II)

Operations with operational credits allow lower minima than the ground facilities alone would support, because the aircraft, the crew or both bring extra capability.

• SA CAT I (special authorisation category I) allows a DH not lower than 150 ft and an RVR that depends on the approach lighting, not lower than 400 m. CS-AWO now contains the airworthiness standard for aircraft flying to these minima.
• SA CAT II (special authorisation category II) is a CAT II approach to a runway that does not meet all the CAT II infrastructure requirements.

Before 2022, EASA called the equivalent operations lower than standard category I (LTS CAT I) and other than standard category II (OTS CAT II). Both terms remain in older manuals and in question banks, where LTS CAT I is tested with an RVR as low as 400 m.

Enhanced flight vision systems (EFVS) earn credits too. Under CAT.OP.MPA.312, an EFVS 200 operation lets an equipped aircraft use reduced RVR minima, but the RVR may not go below 550 m, nor the DH below 200 ft, so EFVS 200 is not a low visibility operation and needs no specific approval. The FAA's 14 CFR 91.176 goes further: EFVS may be used in place of natural vision below the DA or DH, either to 100 ft above touchdown zone elevation or, with the required equipment and authorisation, to touchdown.

Alert height, fail-passive and fail-operational systems

Automatic landing systems are classed by their behaviour after a failure:

• A fail-passive system causes no significant out-of-trim condition or deviation of flight path or attitude after a failure, but the landing is not completed automatically. The pilot takes over, so a DH and visual reference are needed. Airbus annunciates this capability as CAT 3 SINGLE.
• A fail-operational system can still complete the approach, flare and landing automatically after a failure below alert height, the remaining part of the system taking over. Airbus annunciates CAT 3 DUAL. Boeing shows LAND 3 for fail-operational and LAND 2 for fail-passive.

The alert height (AH) is a radio height, set for the aircraft type and its fail-operational landing system. If a failure occurs above it in a redundant part of the landing system, or in the relevant ground equipment, the crew discontinues the approach and goes around. Below it, a single failure no longer stops the landing. Alert height is therefore a failure-management height, not a visual decision point. A fail-operational CAT III approach may be flown with no DH at all; the alert height still applies.

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Eye reference point and cockpit cut-off angle

The design eye reference point is the position for which the manufacturer designed the flight deck view, and markers at each pilot station let the pilot set the seat to it. A pilot sitting too low loses part of the view over the nose, which in fog can mean losing the lights needed at DH.

The cockpit cut-off angle is the angle below the horizontal of the lowest line of sight over the nose. Together with eye height and pitch attitude, it sets the obscured segment, the stretch of ground ahead that the pilot cannot see. The visual segment is what remains between the edge of the obscured segment and the limit of visibility. A higher nose attitude or a lower seat lengthens the obscured segment and shortens the visual segment.

This geometry is why the lowest take-off minima are tied to a visual segment of a set length, not to the RVR alone. On approach, fog is often thicker in the vertical than along the ground (see visibility and RVR), so the slant view at DH can be shorter than the reported RVR suggests.

SMGCS and low visibility taxiing

On the ground, low visibility turns taxiing into the phase with the least margin. A surface movement guidance and control system (SMGCS) is the combination of lighting, markings, signs, procedures and surveillance that keeps aircraft and vehicles on cleared routes. Its key elements are:

• Taxiway centreline lights, alternating green and yellow where they cross the ILS sensitive area or approach a runway.
• Stop bars at runway holding positions, crossed only when switched off.
• Runway guard lights and clearance bars.
• Published low visibility taxi routes.
• Surface movement radar or advanced SMGCS surveillance at larger aerodromes.

The FAA's AC 120-57B set out an SMGCS plan for US airports where scheduled air carriers operate in an RVR below 1,200 ft, and called for taxiway centreline lights, with edge lights on curves, along the taxi routes used below 600 ft RVR. Its 2023 replacement, AC 120-57C, renamed the plan LVO/SMGCS. Crews brief the taxi route on the chart, taxi slowly, read back every holding point and stop to ask when in doubt.

The FAA framework

The FAA reaches similar minima by a different route. Its criteria for take-off, landing and roll-out in all weather are consolidated in AC 120-118 (2018). Air carriers receive their authorisations through operations specifications. The main differences:

The FAA approves SA CAT I and SA CAT II facilities under Order 8400.13, and charts these procedures with a note requiring specific authorisation.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.