Lower than Standard Cat I Approach Operations

This page provides guidance and links to Safety Requirements for Air Traffic Service (ATS) Providers and Aerodrome Licence Holders wishing to implement Lower than Standard CAT I operations.


The current visibility minima for a Category I approach is limited to a Runway Visual Range (RVR) of not less than 550 m and with a decision height (DH) not lower than 200 ft.

Lower than Standard Category I Operations retain the DH criteria above but allow suitably approved aircraft operators to operate down to an RVR of not lower than 400 m depending on the supporting Aeronautical Ground Lighting and the ILS Classification.  For these operations the aircraft is required to have either an auto-land system approved for CAT IIIA operations or an approved Head Up Display Landing System (HUDLS).

The detailed requirements for Lower than Standard Category I Operations are published in EU-OPS, Subpart E (All Weather Operations) Ops 1.430, Appendix 1 (New), paragraph (e).

A summary of the infrastructure requirements in a tabulated form for the various RVR values is available.

A flow diagram to assist in the decision making process for Lower than Standard Category I operations is available here.

Regulatory Requirements

Instrument Landing System

The ILS requirements in Subpart E are written in terms of the ICAO Classification scheme, for example Class I/T1 and II/D/2.   The ICAO classification is published in Annex 10 Volume 1 Radio Navigation Aids Attachment C 2.14.  To assist ATS providers, the EU-OPS Subpart E requirements have been transposed into the equivalent CAP 670 requirements.  As such the CAP 670 ILS 03 EU OPS 1 General Requirements form an acceptable means of compliance.

Note: Class I/T/1 is required for operations to a minimum of 450m RVR. 

Note: Class II/D/2 is required for operations to less than 450m RVR.

ILS Maintenance

It will be necessary to review the maintenance arrangements where the ILS is expected to perform to a higher category.

Aeronautical Ground Lighting (AGL)

The AGL requirements can be found in EU-OPS, Subpart E Appendix 1 (New) Table 6b.

Description of the various approach lighting systems, i.e. Full, Intermediate, can be found in EU-OPS, Subpart E Appendix 1 (New) Table 4.

Note: EU-OPS Standard Day Markings are equivalent to Precision instrument Approach Runway markings in CAP 168 Chapter 7 Aerodrome Signals, Signs and Markings.

Low Visibility Requirements

As lower RVR values will be used at the aerodrome, it will be necessary to review and where necessary revise Low Visibility Procedures (LVPs) in the Aerodrome Manual and the Manual of Air Traffic Services Part 2, to ensure their compatibility with operations at the lower RVR values.

The requirements contained in CAP 493 and CAP 168 Chapter 2 Appendix 2B Low Visibility Operations remain applicable.

ILS Sensitive Area

Where any part of the ILS is required to perform to the requirements for a higher ILS category, then it will be necessary review and confirm that the sensitive areas remain suitable.

CAP 670 ILS 03 provides the requirements for the sensitive area for particular RVR limits.

CAP 670 ILS 10 provides generic requirements for the design and management of the sensitive area.

Runway taxiway Holding Positions

The location of the runway taxiway holding position will have to be reviewed and in some cases relocated to protect any changes to the ILS sensitive area.

The requirement for runway taxiway holding positions to protect the ILS sensitive area can be found in CAP 168 Chapter 7.


No new phraseology has been promulgated for Lower than Standard CAT I.  It is considered that the Low Visibility Procedures will be sufficient for Air Traffic Control (ATC) to manage all aircraft operating to the minimum RVR value.

Instrument Approach Procedure

An Instrument Approach Procedure designed for CAT I operations is suitable for Lower than Standard CAT I.

Runway Visual Range

Even though a lower RVR value is used the operation is still considered to be a CAT I operation. As such the CAT I Instrument Runway Visual Range requirements remain applicable as prescribed in CAP 670 NAV 01.

The Air Traffic Service provider should ensure that the IRVR system can adequately report RVR down to the minimum required.

Pre-Threshold Terrain

EU OPS Subpart E (All Weather Operations) Ops 1.440 (h) Eligible aerodromes and runways states:

For runways with irregular pre-threshold terrain or other foreseeable or known deficiencies, each aeroplane type/runway combination must be verified by operations in standard Category I or better conditions, prior to commencing Lower than Standard Category I, Category II, or other than Standard Category II or Category III operations.

Where the Pre-Threshold Terrain issues exist, which would affect the autoland capability, then a promulgation shall be included in the UK AIP.

Note: HUDLS should not be affected by irregular Pre-Threshold Terrain.

Hazard Identification and Risk Assessment

The Single European Sky Common Requirements state:

Within the operation of the SMS, a provider of air traffic services shall ensure that hazard identification as well as risk assessment and mitigation are systematically conducted for any changes to those parts of the ATM functional system.

Introduction of Lower than Standard CAT I is considered to be a change to the ATM functional system.

As the Lower than Standard CAT I operation is still considered to be a CAT I operation with the same decision height, it is unlikely that there would be any change to existing derived safety requirements.  However the ATS provider still needs to confirm that the derived requirements remain valid for the new operation and record this in the safety documentation.

Where an ATS provider identifies changes to an existing requirement or any additional requirements then these must be addressed through the normal SMS processes.

Safety Assurance Documentation

Safety Assurance Documentation shall be prepared in accordance with the ATS providers SMS.  The Air Traffic Service provider may wish to use a compliance matrix to demonstrate that each requirement of CAP 670 has been met.


To assist Aircraft Operators to assess whether the aerodrome infrastructure and Low Visibility Procedures are acceptable for a particular operation, it will be necessary to promulgate in the AIP section AD 2.20 Section 6 “Use of Runways” the operations that are being offered.

Examples of AIP entries are shown below.

Runway XX suitable for Lower than Standard Category I operations supported by an ILS Classification of II/D/2.

Note: Work is on-going with in the CAA to develop a dedicated EU OPS heading in AD 2.20.

Related Information