Cloud Separation Rules

Definition

Cloud separation rules define the minimum required distances between an aircraft and clouds during VFR (Visual Flight Rules) operations. These rules ensure that a pilot flying without reference to instruments maintains sufficient visibility and space to avoid terrain, other aircraft, and weather hazards.

Purpose

  • Prevent VFR aircraft from unintentionally entering IMC (Instrument Meteorological Conditions)
  • Ensure see-and-avoid remains possible at all times
  • Maintain legal compliance with VFR operating minima
  • Protect separation between VFR and IFR traffic in mixed airspace

Core Components of Cloud Separation

There are typically three key requirements under VFR:

  • Minimum visibility (horizontal)
  • Minimum distance from clouds (vertical and horizontal)
  • Visual contact with the ground or horizon (in some cases)

The specific values depend on:

  • Airspace class
  • Altitude
  • Type of airspace (controlled vs uncontrolled)
  • Whether the flight is inside or outside controlled airspace

Standard ICAO Cloud Separation Minima (Above 3000 ft AMSL or 1000 ft AGL)

Airspace Visibility Horizontal from Cloud Vertical from Cloud
Classes C, D, E, F, G
(above 3000 ft AMSL or 1000 ft AGL)		 5 km 1500 m 1000 ft

In Class B (where VFR is allowed):

  • Visibility: 5 km
  • Clear of cloud and in sight of the surface

Below 3000 ft AMSL / 1000 ft AGL (Class F & G)

In some countries (including EASA states), reduced VFR minima are allowed below these thresholds in uncontrolled airspace, such as:

  • Visibility: 5 km (or even 1.5 km for aircraft ≤140 kt)
  • Cloud clearance: Clear of cloud and in sight of the surface

These allowances are often referred to as “VFR Special Rules” and depend on national regulations.

Special VFR (SVFR)

  • Inside control zones (CTR), VFR flights may be permitted with lower minima
  • Requires explicit SVFR clearance from ATC
  • Typical minima: 1500 m visibility (or 800 m for helicopters), clear of cloud, in sight of surface
  • Often used for VFR departures in marginal weather

Flight at or above FL100 (10,000 ft)

  • In some FIRs, higher visibility is required:
  • Visibility: 8 km
  • Cloud separation remains the same

These values help compensate for increased speed and closing rates at high altitude.

Key Phraseology Examples

  • “Unable VFR due to cloud separation minima”
  • “Request Special VFR for departure from control zone”
  • “Maintaining visual separation, clear of cloud”

Tips for VFR Pilots

  • ✅ Always cross-check forecast weather and real conditions
  • ✅ Be aware of airspace boundaries where cloud minima change
  • ✅ Never enter cloud unless you are cleared and qualified for IFR