This article has been divided into 7 parts:
  1. What is LVP (Low Visibility Procedure)
  2. What are RVR (Runway Visual Range)
  3. What is Visibility
  4. What is SP (Safeguarding Procedures)
  5. Low Visibility Procedures
  6. Description of equipment and services taking Delhi Airport as example
  7. Cancellation of Safeguarding Procedures (SP) and Low Visibility Procedures (LVP)

 1. What is LVP?

Low Visibility Procedures are the actions to ensure the safe operation of aircraft during periods of reduced visibility or low cloud base. These include specific procedures applied at an aerodrome for the purpose of ensuring safe operations during Categories II and III approaches and/or low visibility take-offs.

LVP shall only be implemented when Safeguarding Procedures (SP) has been completed and the airport is configured for low visibility operations.

Based on the RVR and visibility at certain locations weather or not implementation of LVP is required is decided upon.

2. What is RVR?             

(Runway Visual Range) The range over which the pilot of an aircraft on the centerline of a runway can see the runway surface markings or the lights delineating the runway or identify its centerline.

2.1 Reporting of RVR Values at appropriate locations based on category of operations

Touch-down zone RVR needs to be reported for Cat I operations,

touch-down and mid zone RVR for Cat II operations,

touch-down, mid and roll-out zone RVR for Cat III operations.

In all cases, touch-down zone will always be controlling, however if any other RVR is reported and is relevant (operator shall not define relevant depending on runway length/aircraft stopping distance unless approved by FSD, DGCA) it also becomes controlling. The mid zone and roll-out zone can be lower than the touch-down zone provided conditions enumerated below are met.

Type of OperationRVR
 Touch-down ZoneMid zoneRoll-out zone
CAT I550 M125 M125 M
CAT II300 M125 M125 M
CAT III A175 M125 M125 M
CAT III B (with roll-out guidance)75/50 M75/50 M75/50 M

Note: The use of minimum RVRs in the table above is subject to:

  • operator authorization;
  • aeroplane authorization;
  • flight crew training and qualification; and
  • aerodrome facilities.

Note: The use of minimum RVR of 75m or 50m depends on value approved for operators and aeroplanes rollout guidance system.

3. What is Visibility?

Meteorological Service for International Air Navigation defines
visibility for aeronautical purposes as the greater of the greatest distance at which:
a) a black object of suitable dimensions, situated near the ground, can be seen and recognized when observed against a bright background; and
b) lights in the vicinity of 1 000 candelas can be seen and identified against an unlit background.

4. What is SP?

Safeguarding Procedures are instructions for relevant airport departments and airside operators to prepare ground services and facilities for low visibility operations, in order that when LVP are implemented all SP are complete and airport is configured for Low Visibility Procedures and Low Visibility Take-offs.

LVTO: (Low Visibility Take Off) A term used in relation to flight operations referring to a take-off on a runway where the RVR is less than 400m.

Note: So, before the implementation of LVP, SP is implemented to make aerodrome safe for LVP operations.


Criteria for Safeguarding Procedures:

Safeguarding Procedures shall be initiated when the runways in use has:

  1. The RVR is less than 1200 m or visibility is forecast to deteriorate to 800m or less;and/or
  2. The cloud ceiling is 400 ft and forecast to fall to 200 ft or less.

Criteria for implementation of Low Visibility Procedures:

Low Visibility Procedures shall be implemented when –

  1. Either, TDZ, MID or END RVR is less than 800 m; and/or Cloud ceiling is less than200 ft; and
  2. Safeguarding Procedures (SP) have been completed and the airport is safeguarded.

(Note: Though LVP is implemented when RVR is less than 800m, ILS CAT I operation will continue till TDZ RVR is not less than 550m)

5.1 LVP Operations

5.1.1 Aerodrome Control Procedures

  • Arriving aircraft shall be issued landing clearance not later than 2NM from touchdown. If landing clearance cannot be issued when the aircraft is 2NM from touchdown it shall be instructed to carry out a missed approach.
  • Arriving aircraft should be given unimpeded taxi route to allow it to clear the localizer sensitive area expeditiously.
  • Landing clearance shall not be issued until:
    1. A preceding landing aircraft has vacated Localizer Sensitive Area [LSA] AND confirmed by the pilot.
    2. A preceding departing aircraft is airborne and has passed over the localizer antenna.
  • The LSA in front of an arriving aircraft shall not be infringed from the time it is 2NM from the touchdown until it has completed its landing roll.

5.1.2 Surface Movement Control Procedures

  • Pilots need additional guidance and information when taxiing during periods of reduced visibility.
  • Taxiing aircraft should be routed in accordance with the prescribed Low Visibility Routes to ensure a simple one-way traffic flow is maintained, however it may be necessary for operational reasons to sometimes route aircraft via alternative taxiways.
  • AGL (aeronautical ground lights) team / Follow Me vehicles shall monitor the status of taxiway lights and immediately advise ATC Tower of any unserviceability affecting the taxiways during LVP operations.
  • During the period of LVP, the lights on taxiways that are not being used may be switched off.
  • Surface Movement Controller should monitor the progress of arriving aircraft on ASMGCS Display as they vacate the runway after landing and ensure that they do not stop within the Localizer Sensitive Area [LSA]. Pilots shall report runway vacated on RTF when the aircraft has reached the color coded part of the exit taxiway centerline light after making allowance for aircraft size to ensure that the entire aircraft is clear of the ILS sensitive area.
  • Vehicle movement, when RVR is less than 550m, should be restricted. Only operationally essential vehicle duly authorized by Apron Control should be permitted to operate on the maneuvering area. These vehicles shall remain outside the Localizer Sensitive Area [LSA].
  • Any movement of vehicle on the maneuvering area shall be coordinated with ATC. During CAT II/ CAT III operations, vehicles fitted with transponders (vehicle locators) should only be permitted on the maneuvering area. However, other vehicles crossing taxiways on service road and taxiways must be regulated by official of apron control deploying manpower.

5.1.3 Approach/ Radar Control Procedures

In addition to the information normally transmitted by Approach Radar Controller must initiate, the information specifying the unserviceability, if any, of any component parts of CAT II/CAT IIIA/IIIB facilities not previously broadcast on ATIS for publication.

During LVP the Approach Radar Controller must have the following information

  1. Status of ILS
  2. Serviceability of visual aids  
  3. RVR information of TDZ, MID and END.
  • Approach/Radar Controller should vector the arriving aircraft to intercept the localizer at a distance not less than 10NM from touchdown.
  • Suitable spacing between the arriving aircraft may be provided to ensure that the arriving aircraft can be given a landing clearance by 2 NM from touchdown. If there is a departure between the two arrivals, the spacing between the arriving aircraft may be suitably increased to ensure that the departing aircraft passes overhead the Localizer before the inbound aircraft reaches 2NM from touchdown.
  • Approach Radar Controller shall not subject an aircraft carrying out CAT II/CAT IIIA/CAT IIIB approaches to any speed control when within 20NM from touchdown.

5.1.3 Lighting Inspection Procedures

  • The appropriate aeronautical ground lights must have been inspected during the hour preceding implementation of LVP. AGL team to carry out close monitoring of serviceability of AGL through monitoring system.
  • Operations Duty Manager is responsible for organizing lighting inspections. He shall arrange an inspection of the relevant aeronautical ground lighting. To ensure minimum delay in completing the inspection, separate teams may inspect the landing runway, associated taxiways and apron area and confirm that they are clear of runway/taxiway/apron to ATC.
  • For SP and LVP only the lighting for the active runway and associated taxiways are inspected

5.1.4 Action by Other agencies at airport such as – Airlines, Re-fuelling Companies,Catering Agencies, Airport Police, Customs, Immigration, Health

  • All agencies operating in the operational area shall ensure that minimum number of their vehicles, as are absolutely essential for aircraft operations, operate in the operational area. The drivers of these vehicles should keep a look out for taxing aircraft and other vehicles to prevent incident/ accidents. During CAT IIIB operations only vehicles equipped with serviceable transponder shall be permitted to operate in manoeuvring area.
  • All the vehicles must have their obstruction/ anti-collision lights “ON” during operation of low visibility procedures.

6. Description of equipment and services taking Delhi Airport as example

6.1 Measurement of  Runway Visual Range (RVR)

  • There are three transmissometers for RWY 28 to record RVR values. One transmissometer is located each at touchdown zone, runway midpoint, and end of runway. RVR values always refer to Touchdown RVR (TDZ), Mid-point RVR (MID) and Stop End RVR (END).
  • RWY 29/11 has 5 transmissometers at following locations:
    1.  Physical beginning of RWY-29, termed as ‘A’
    2. Near displaced threshold of RWY-29, termed as ‘B’
    3. Mid of RWY 11/29, termed as ‘C’
    4. Near displaced threshold of RWY-11, termed as ‘D’
    5. Physical beginning of RWY-11, termed as ‘E.

6.2 Aeronautical Ground Lighting (AGL) System

  • The Precision Approach lighting system for CAT II/CAT IIIA/CAT IIIB operations are installed on RWY 28, RWY 29, and RWY 11 at IGI Airport.
  • During LVP operation irrespective of the RVRs, the state electricity board (BSES) power supply is the primary source through online UPS for the systems which require a maximum of one second switchover time and the DGs are in auto operation mode to meet the requirements in case of power failure. The power changeover for the other systems which are not covered with UPS backup get the power supply through DGs within 15 seconds from the time of power failure. For the systems covered with UPS back up, the changeover are zero seconds. There is no specific requirement for keeping the DG source as primary source when BSES power source is available during the LVP operations.

6.3 Non-Visual Ground Surveillance System

  • IGI Airport is equipped with Surface Movement Radar. The system provides nonvisual electronics surveillance of manoeuvring area and facilitates the controllers to identify potential ground conflict and runway incursions.
  • For CAT IIIA/CATIIIB and CAT II operations below 350m availability of Non-Visual Surveillance System such as Surface Movement Radar is mandatory.

6.4 Navigational Aids

 RWY 28, RWY 11, and RWY 29 have been equipped with Instrument Landing System (ILS) for CATII/CATIIIA/CAT IIIB.

The ILS Category Monitor Panel at the Control Tower console indicates the ILS category availability by monitoring the following equipment:

  1. Main and standby localizer transmitters
  2. Main and standby glide path transmitters

The status of the following facilities is monitored and displayed by a separate nav-aid status indicator panel:

  • Outer Marker

ILS equipment serviceability required for CAT II/CAT IIIA/CAT IIIB operations: –

  • Both main and standby localizer transmitters;
  • Both main and standby glide path transmitters;
  • One standby power generator in each unit.
  • Outer marker/ ILS DME

NOTE 1 – Unserviceable ILS DME does not change the status of ILS provided OM and Glide Path are serviceable for runway 28 only.

NOTE 2 – Unserviceable Outer Marker does not change the status of ILS provided ILS DME is operational for runway 28 only.

6.5 Airport Rescue and Fire Fighting Service (ARFF)

During SP following predetermined positions will be taken by ARFF vehicles

  1. One CFT north of RWY28/10 near TWY D1
  2. One CFT north of RWY28/10 near TWY E
  3. One CFTs north of Z opposite Z5
  4. In the event of an incident when LVP are in force, ADC and SMC should provide the maximum assistance in directing ARFF to required location.

6.6 Vehicular movement

  1. Vehicles are not be cleared to cross the runway, once an inbound aircraft is 8NM from touchdown.
  2. Vehicular movement on the manoeuvring area are to be restricted to essential vehicles.
  3. During CATII /CAT III operations only vehicles equipped with transponder (Vehicle Locator) operate in manoeuvring area. However, other vehicles crossing taxiways on service road are regulated by official of Apron Control by deploying man power.
  4. Vehicles must not be held at any point closer to the runway than the CAT II/ CATIIIA/CAT IIIB holding point/stop-bar.

LVTO (Low Visibility Take off) pertains to take off when the RVR is below 400 m and is applicable whenever the reported RVR in any zone (touch-down/mid/roll-out RVR) is below 400 m (e.g. if the RVR is 400/300/300 representing the three zones, then the 300 m will be the RVR for reckoning facilities and conditions.  If the RVR is 300/150/Not Reported, then 150 m will be the reckoning RVR for facilities.

7. Cancellation of Safeguarding Procedures (SP) and Low Visibility Procedures (LVP)

WSO may terminate LVP when –

  • Meteorological conditions improve and TDZ, MID and END RVR are 800 m or more and the cloud ceiling is 200 ft or higher, and trend is for improvement for both runways.
  • Facilities and equipment necessary for CAT II/CAT IIIA/CAT IIIB operations are degraded and/or the prevailing conditions are considered unsafe for such operations.
  • WSO should consult Meteorological Office for forecast before cancelling SP and LVP.
  • On cancelling LVP, Aerodrome Control shall include it in the subsequent two ATIS broadcasts that “LOW VISIBILITY PROCEDURES ARE CANCELLED”. Aerodrome Tower Controller will inform all the concerned agencies.
  • If SP are completed and LVP are not subsequently implemented and meteorological conditions improve and the visibility/RVR is more than 1200 m and the cloud ceiling is 400 ft or higher and both are forecast to remain above the required SP criteria, WSO may cancel SP.


6 thoughts on “The Low Visibility Procedures

  1. I suggest one thing that plz provide diagram with every concept or you can make small video to justify the concepts like in RVR how it work at runway can be more clear by diagram or video.
    but other explanation is very clear to me .

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