Continuous Monitoring Program, Flight Parameters Deviation Calls during LVO Approach and Alert Height (AH) Concept

Continuous Monitoring Program

After obtaining the initial authorization, approved LVO must be continuously monitored to detect any undesirable trends before they become hazardous. The Company has established a procedure to monitor the performance of the automatic landing system to touchdown performance of each aeroplane.

To collect the data, the Company should provide the flight crews with adequate documents.

The following information shall be retained for a period of 12 months:
• Total number of approaches, where the airborne equipment was utilised to make actual or practice approaches to the applicable Category II/III minima;
• Reports of unsatisfactory approaches and/or automatic landings, by aerodrome and aeroplane registration, classified in airborne equipment faults, ground facility difficulties, ATC reasons or other reasons.

The Company must analyse results and, if necessary, take the adequate actions (modification of SOPs and/or maintenance procedures).

Note: Continuous monitoring also permits detection of problems on a specific aerodromes (ILS, ATC procedures, etc.).

Flight Parameters Deviation Calls during LVO Approach

Refer to OM Part B.

Loss of Required Visual References

Decision Height (DH) Concept

It should be stressed that decision height (DH) is the lower limit of the decision zone during which, in limiting conditions, CM1 will be assessing visual references. CM1 should come to this zone prepared for a go-around but with no pre-established judgement. CM1 should make a decision according to a quality of approach and way visual references develop as DH is approached. In CAT II operations and CAT III operations with DH, conditions required at DH to continue approach are: adequate visual references to continue approach and land, and acceptable flight path. If both these conditions are not satisfied, it is mandatory to initiate a missed approach.

If the decision to continue has been made and visual references subsequently become insufficient, or flight path deviates unacceptably, a go-around must be initiated (a go-around initiated at low altitude, whether auto or manual, may result in ground contact). If visual references are lost after touchdown, a go-around should not be attempted. A rollout should be continued with AP in ROLLOUT mode down to taxi speed.

Alert Height (AH) Concept

Alert height (AH) is a height defined for Category III operations with a fail-operational landing system.

Above AH, a go-around must be initiated if a failure affects the fail-operational landing system. The list of these failures is contained in the AFM/FCOM.

Below AH, the approach will be continued (except if AUTOLAND warning is triggered). The AH is evaluated during aircraft certification; it is set at 100 feet for A320 aircraft. This is the value at which the flight crew makes a decision to land during CAT IIIB approach with NO decision height.

If the decision to continue has been made and AUTOLAND warning is triggered, a go-around must be initiated (a go-around initiated at low altitude, whether auto or manual, may result in ground contact).

Failures and Associated Actions

In general, there are three possible responses to the failure of any system, instrument or element during an approach:

• CONTINUE approach to planned minima, or
• REVERT to higher minima and proceed to new minima, or
• GO-AROUND and reassess the capability.

A nature of failure and point of its occurrence will determine which response is appropriate. As a general rule, if a failure occurs above 1000 ft AGL, an approach may be continued reverting to a higher DH, providing appropriate conditions are met. Below 1000 ft AGL and down to DH an occurrence of any failure implies a go-around and reassessment of system capability. Another approach may then be undertaken to appropriate minima for given aeroplane status. It has been decided that below 1000 ft AGL, not enough time is available for a crew to perform necessary switching, to check system configuration and limitations and brief for minima.

ATC Procedures

LVO (LVTO, CAT II and CAT III) require special procedures for ATC and all services on aerodrome (maintenance, security, etc.). They are often referred to under a generic name of Low Visibility Procedures (LVP). LVP are put into force at aerodromes authorised for Category II / III operations latest when the RVR falls below 550m and/or the cloud base falls below 200ft. Each aerodrome authority develops its own procedures with the ICAO All Weather Document (or ECAC No 17) as the possible aid. Flight crews shall refer to OM Part C for specific aerodrome-related LVP instructions and/or information.