Low visibility definitions

LOW VISIBILITY OPERATIONS

– Weather minima:

It is the limits of usability of an aerodrome for take or landing in terms of  visibility or runway visual range. It consider to be at low visibility conditions ( LVO) when the RVR is less than 400m

   There are different types of weather minima:

• Airfiel operating minima : established in accordance with the airport authority and publish on the approach charts.
• Operator´s minima: Lowest minima that an operator is allowed to use at a specific airfield.
• Crew minima : Lowest minima that an crew is allowed to use at a specific airfield.
• Aircraft minima : Certification of the aircraft.   

– Runway visual Range ( RVR):

Is the range over which a pilot of an aircraft on the centreline of the runway can see the runway surface markings or the lights delineating the runway or identifying  its centreline. It is measured by the transmissometers located at 

• The touch-down zone ( TDZ).
• The mid runway portion ( MID).
• The roll-out portion or stop-end.

          note: ICAO recomends that RVR reports are given with 50m increments when the RVR is less than 800m, and 25m when the RVR is less than 150m. Any change of                                                                      RVR value must be kwonn by the ATC in less than 15 seconds.

– Precision approach:

An approach and landing using instruments for navigation guidance based on an instrument approach procedure. It gives accurate track guidance (azimuth) during the final approach segment and information concerning height above the threshold. (ILS)

– Non precisión approach:

An instrument approach procedure designed for 2D instrument approach . Where there is no ground equipment that can provide height ( elevation) data to the aircraft

– Minimun Decision heigh (MDA):

The Minimum Descent Altitude (MDA) or Minimum Descent Height (MDH) is a specified altitude or height in a Non-Precision Approach or Circling Approach below which descent must not be made without the required visual reference.

– Decision height (DH):

is the height at which the pilots should have runway visuals to continue the landing in a instrumental approach. If runway is not visible, we must perform a  Missed Approach.