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System Minima

Definition: Height derived for the lowest permitted DH or MDH taking into account the characteristics of the ground and airborne equipment. System minima are related to the type of approach and are standard figures for precision and non-precision approaches.

Non-precision Approach

An operator must ensure that system minima for non-precision approach procedures, which are based upon the use of ILS without glidepath (LLZ only), VOR, NDB, SRA, and VDF are not lower than the MDH values given in Figure 5.4.

System minima

Facility	Lowest MDH
Localiser with or without DME	250 ft
SRA terminating at 0.5 NM	250 ft
SRA terminating at 1 NM	300 ft
SRA terminating at 2 NM	350 ft
VOR	300 ft
VOR/DME	250 ft
NDB	350 ft
VDF (QDM and QGH)	350 ft
NDB/DME	300 ft
RNAV/LNAV	300 ft

Figure 5.4 Non-precision system minima

Minimum Descent Height

An operator must ensure that the minimum descent height for a non-precision approach is not lower than either the OCH/OCL for the category of aeroplane; or the system minimum. MDH (and OCH) are based on the aerodrome elevation, which is a specified point on the aerodrome, often just in front of the tower. Since runways often have a slight gradient (slope) the elevation of the thresholds of runways could be considerably higher, or lower than the stated elevation of the airfield. If the threshold elevation is 2 metres or more BELOW the threshold of the airfield, MDH is measured from the threshold rather than the airfield.

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Visual Reference

A pilot may not continue an approach below MDA/MDH unless at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:

•Elements of the approach light system.

•The threshold.

•The threshold markings.

•The threshold lights.

•The threshold identification lights.

•The visual glide slope indicator.

•The touchdown zone or touchdown zone markings.

•The touchdown zone lights.

•Runway edge lights, or

•Other visual references accepted by the Authority.

Required RVR

A non-precision approach (NPA) operation is an instrument approach using any of the facilities described in Figure 5.4 (System minima), with an MDH or DH not lower than 250 ft and an RVR/CMV of not less than 750 m, unless accepted by the Authority. An APV operation is an instrument approach which utilizes lateral and vertical guidance, but does not meet the requirements established for precision approach and landing operations, with a DH not lower than 250 ft and a runway visual range of not less than 600 m unless approved by the Authority. RVR for approaches must be greater than minima at the threshold. (For take-off, all 3 RVR must be within limits)

Precision Approach - Category I Operations

A Category I operation is a precision instrument approach and landing using ILS, MLS, GLS (GNSS/GBAS) or PAR and with an RVR not less than 550 m unless accepted by the Authority. An operator must ensure that the decision height to be used for a Category I precision approach is not lower than:

•The minimum decision height specified in the AFM if stated.

•The minimum height at which the precision approach aid can be used without the required visual reference.

•The OCH/OCL for the category of aeroplane; or

•200 ft.

A pilot may not continue an approach below the Category I decision height, unless at least one of the visual references listed above is visible.

Minimum RVR /CMV/visibility for Category I, APV and non-precision approaches can be derived from the following formula;

Required RVR/visibility (m) = [(DH/MDH (ft) × 0.3048)/tan α] – length of approach lights (m)

Note 1: α is the calculation angle, being a default value of 3° increasing in steps.

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This means that RVR is dependent upon the actual DH/MDH, and the lighting facilities available at the aerodrome. However, unless authorized by the Authority, the lowest RVR for a Cat I Approach is 550 m. When authorized (Lower than Standard Cat I) the absolute minimum RVR, depending on the class of lighting facility, can be 400 m

For single-pilot operations, an operator must calculate the minimum RVR for all approaches in accordance with the appropriate tables found in EU-OPS. (These tables are not required knowledge for students.) However, for single pilot operations, the minimum RVR is 800 m, except when using a suitable autopilot coupled to an ILS or MLS, or an approved HUDLS (including EVS), in which case normal minima apply.

Precision Approach - Category II Operations

A Category II operation is a precision instrument approach and landing using ILS or MLS with:

•Decision height below 200 ft but not lower than 100 ft; and

•Runway visual range of not less than 300 m.

An operator must ensure that the decision height for a Category II operation is not lower than:

•The minimum decision height specified in the AFM, if stated.

•The minimum height to which the precision approach aid can be used without the required visual reference.

•The OCH/OCL for the category of aeroplane.

•The decision height to which the flight crew is authorized to operate, or

•100 ft.

A pilot may not continue an approach below the Category II decision height unless visual reference containing a segment of at least 3 consecutive lights being the centre line of the approach lights, or touchdown zone lights, or runway centre line lights, or runway edge lights, or combination of these is attained and can be maintained. This visual reference must include a lateral element of the ground pattern, i.e. an approach lighting crossbar or the landing threshold or a barette of the touchdown zone lighting unless the operation is conducted utilising an approved HUDLS to touchdown.

The lowest minima to be used by an operator for Category II operations are:

Category II minima

		Autocoupled/Approved HUDLS to below DH (note 1)
	Decision Height
		RVR	RVR
		(Category A, B, C)	Category D
	100 - 120 ft	300 m	300 m (note 2) / 350 m
	121 - 140 ft	400 m	400 m
	141 ft and above	450 m	450 m

Figure 5.5: RVR for Cat II approach vs DH.

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Notes:

1.This reference to ‘autocoupled to below DH/Approved HUDLS’ in this table means continued use of the automatic flight control system down to a height which is not greater than 80% of the applicable DH. Thus airworthiness requirements may, through minimum engagement height for the automatic flight control system, affect the DH to be applied.

2.300 m may be used for a Category D aeroplane conducting an autoland.

Precision Approach - Category III Operations

Category III operations are subdivided as follows:

•Category III A operations: A precision instrument approach and landing using ILS or MLS with decision height lower than 100 ft; and runway visual range not less than 200 m.

•Category III B operations: A precision instrument approach and landing using ILS or MLS with decision height lower than 50 ft, or no decision height; and runway visual range lower than 200 m but not less than 75 m.

•Category III C operations: A precision instrument approach and landing using ILS or MLS with no decision height and no runway visual range requirements.

Note: Where the DH and the RVR do not fall within the same Category, the RVR will determine in which Category the operation is to be considered.

For operations in which decision height is used, an operator must ensure that the decision height is not lower than:

•The minimum decision height specified in the AFM, if stated.

•The minimum height to which the precision approach aid can be used without the required visual reference; or

•The decision height to which the flight crew is authorized to operate.

No Decision Height Operations

Operations with no decision height may only be conducted if:

•The operation with no decision height is authorized in the AFM.

•The approach aid and the aerodrome facilities can support operations with no decision height; and

•The operator has an approval for CAT III operations with no decision height.

Note: In the case of a CAT III runway it may be assumed that operations with no decision height can be supported unless specifically restricted as published in the AIP or NOTAM.

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