Low visibility procedures (LVP)

Low Visibility — Procedures and Hazards

This lesson covers both Low Visibility Procedures (LVP) at airports and VFR-relevant hazards in reduced visibility (fog, icing, cloud base).

Part 1 — LVP at airports

LVP are operational measures at airports under sharply reduced visibility, to ensure the safety of approach, landing, and ground movements.

Source: ICAO Annex 14 Volume I; ICAO Doc 9476 Manual of Surface Movement Guidance and Control Systems (SMGCS); EASA AMC 20-25.

When are LVP activated?

Typical triggers (vary by airport / state):

• RVR < 600 m (or similar).
• Cloud base < 200 ft AAL (Cat II conditioned).
• Planned CAT II/III approaches.

LVP activation is announced in ATIS: "Low Visibility Procedures in operation."

Ground effects

• Larger holding distances: aircraft wait further from the runway edge (CAT III holding position).
• Reduced surface movement: only one aircraft on certain taxiways at a time.
• Extended runway protection zones (ILS critical area, ILS sensitive area) — no traffic inside.
• Runway lights at high intensity.

Airborne effects

• Increased separation between approaching aircraft.
• Only LVP-approved aircraft (CAT II/III avionics) for approaches < CAT I minima.
• VFR traffic in CTR during LVP typically not permitted or sharply restricted.

For PPL-VFR — practical consequences

LVP affects VFR directly:

• VFR flights into an LVP-active CTR: typically not permitted.
• Approach from outside: ATC can refuse VFR approach.
• Alternate needed — plan before flight.

Pre-flight check: current METAR/TAF of the destination for expected LVP activity.

Cat I / II / III — approach categories

(Recap from Subject 060 Lesson "ILS Awareness"):

LVP usually activated at RVR < 600 m or before CAT II approach.

Part 2 — VFR hazards in reduced visibility

Warm-front passage — main VFR hazard

When flying through a warm front, the main hazard for a VFR pilot is a strong reduction in visibility with violation of visual flight conditions (VMC):

• Warm fronts bring extended nimbostratus and stratus decks — visibility may drop to a few hundred metres.
• Drizzle further reduces visibility.
• Low cloud bases (often < 1000 ft AGL) press the VFR pilot toward the ground.
• Consequence: with a warm front along the route or at the destination: divert or postpone the flight.

Temperature approaching dew point in the evening — fog

When the air temperature in the evening hours approaches the dew point (e.g. after a hot, sunny day with high ground moisture), the pilot must expect dense surface fog:

• After sunset the ground cools rapidly by radiation.
• The air directly above the ground cools too and condenses on reaching the dew point.
• Result: radiation fog in the first hours after sunset or before sunrise.
• Consequence: end the flight before fog forms, or divert to a fog-free airfield.

→ Rule of thumb: temperature/dew-point spread < 3 °C in the evening = high fog risk.

Supercooled rain — severe icing

Supercooled rain / freezing rain is an extreme icing hazard: liquid rain below 0 °C that freezes instantly on contact with the cold aircraft.

• Massive ice build-up in a very short time on all surfaces — aerodynamic and static values change dramatically.
• Clear ice is especially dangerous — barely visible, very heavy.
• Effects: wing profile destroyed (lift loss > 50 %), control surfaces stiffened, pitot/static blocked.
• VFR consequence: if freezing rain is suspected, immediately turn back or descend into warmer air (if possible); consider emergency landing.

Icing zone — leave quickly

If the aircraft enters an icing zone (visible ice build-up on wing leading edges, pitot, antenna), the pilot must leave the zone as quickly as possible:

• Change altitude: often up or down (warmer or drier layer).
• Change heading: shortest path out of the cloud/precipitation zone.
• Carb heat ON immediately.
• Pitot heat ON (if equipped).
• If equipped, anti-ice / de-ice activated.
• Mayday/PAN-PAN depending on severity.

Rime ice on the wing — effects

Rime ice on the wing dramatically changes the lift profile and has the following main effects:

The greatest danger of wing icing by rime ice is the combination of:

1. Change of airfoil shape (aerodynamics disturbed),
2. Mass increase (additional weight),
3. Drag increase (higher fuel consumption, worse performance),
4. Loss of lift (resulting from all the above combined).

→ The pilot must assess icing conditions before entering cloud at sub-zero temperatures and abort or re-route the flight as needed.

European specifics

• Major airports (LHR, CDG, FRA, AMS, MUC, ZRH): full LVP infrastructure.
• Regional airports: often only CAT I equipment — at low visibility closed for IFR approach.
• Small airfields (UL, sport): no LVP — closed in fog for all traffic except authorised.