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Visual References

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Article Information
Category: Controlled Flight Into Terrain Controlled Flight Into Terrain
Content source: Flight Safety Foundation Flight Safety Foundation (FSF)
Content control: EUROCONTROL EUROCONTROL

Description

The phrase 'Required Visual Reference' is used in relation to the transition from control of an aircraft by reference to flight deck instrumentation to control by reference to external visual references alone. Those visual references, including aids, should have been in view for sufficient time for the pilot to have made an assessment of the aircraft position and rate of change of position in relation to the desired flight path. In Category III operations with a decision height the required visual reference is that specified for the particular procedure and operation. (ICAO Annex 6, and PANS-ATM).

The establishment of visual references at the completion of an instrument approach is an important process which determines whether the approach may be continued to landing, or a go-around must be flown.

Note: the vertical or slant view of the ground through broken clouds or fog patches does not constitute an adequate visual reference to conduct a visual approach or to continue an approach below the applicable MDA/H or DA/H.

The section below headed "European Regulations" details what these visual references must be. The remainder of this article deals with the process of transition within the aircraft cockpit.

According to Flight Safety Foundation (FSF) Approach-and-landing Accident Reduction (ALAR) Briefing Note 7.3 — Visual References , "The transition from instrument references to external visual references is an important element of any type of instrument approach."

The briefing note points out that two common Task task-sharing philosophies are common:

  • "Pilot flying-pilot not flying (PF-PNF) task-sharing with differences about the acquisition of visual references, depending on the type of approach and on the use of automation:
    • Nonprecision and Category (CAT) I instrument landing system (ILS) approaches; or,
    • CAT II/CAT III ILS approaches (the captain usually is the PF, and only an automatic approach and landing is considered); and,
  • "Captain-first officer (CAPT-FO) task-sharing, which usually is referred to as a shared approach, monitored approach or delegated-handling approach.

"Differences in the philosophies include:

  • The transition to flying by visual references; and,
  • Using and monitoring the autopilot."

"The task-sharing for the acquisition of visual references and for the monitoring of the flight path and aircraft systems varies, depending on:

  • The type of approach; and,
  • The level of automation being used:
    • Hand-flying (using the Flight Director [FD]); or,
    • Autopilot (AP) monitoring (single or dual AP)."

The briefing note than proceeds to discuss task sharing and other considerations for different types of approach.

European Regulations

AMC1 to IR-OPS CAT.OP.MPA.305(e) and Appendix 1 to EU-OPS 1.430 define the required visual references for continuion of a precision approach or a non-precision approach as follows:

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

(i) Elements of the approach light system;
(ii) The threshold;
(iii) The threshold markings;
(iv) The threshold lights;
(v) The threshold identification lights;
(vi) The visual glide slope indicator;
(vii) The touchdown zone or touchdown zone markings;
(viii) The touchdown zone lights;
(ix) Runway edge lights; or
(x) Other visual references accepted by the Authority.

Precision Approach A pilot may not continue an approach below the Category I decision height ... unless at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:

(i) Elements of the approach light system;
(ii) The threshold;
(iii) The threshold markings;
(iv) The threshold lights;
(v) The threshold identification lights;
(vi) The visual glide slope indicator;
(vii) The touchdown zone or touchdown zone markings;
(viii) The touchdown zone lights; or
(ix) Runway edge lights.

Category II Operations 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 a 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.

Category IIIA Operations For Category IIIA operations, and for Category IIIB operations with failpassive flight control systems, a pilot may not continue an approach below the decision height ... unless a visual reference containing a segment of at least 3 consecutive lights being the centreline of the approach lights, or touchdown zone lights, or runway centreline lights, or runway edge lights, or a combination of these is attained and can be maintained.

Category IIIB Operations For Category IIIB operations with fail-operational flight control systems using a decision height a pilot may not continue an approach below the Decision Height ... unless a visual reference containing at least one centreline light is attained and can be maintained.

Accidents and Incidents

The following events on SKYbrary involve lack of visual reference as a factor:

  • A332, vicinity Tripoli Libya, 2010 (On 12 May 2010, an Afriqiyah Airways Airbus A330 making a daylight go around from a non precision approach at Tripoli which had been discontinued after visual reference was not obtained at MDA did not sustain the initially established IMC climb and, following flight crew control inputs attributed to the effects of somatogravic illusion and poor CRM, descended rapidly into the ground with a high vertical and forward speed, The aircraft was destroyed by impact forces and the consequent fire and all but one of the 104 occupants were killed.)
  • A320, Jaipur India, 2014 (On 5 January 2014, an Airbus A320 was unable to land at Delhi due to visibility below crew minima and during subsequent diversion to Jaipur, visibility there began to deteriorate rapidly. A Cat I ILS approach was continued below minima without any visual reference because there were no other alternates within the then-prevailing fuel endurance. The landing which followed was made in almost zero visibility and the aircraft sustained substantial damage after touching down to the left of the runway. The Investigation found that the other possible alternate on departure from Delhi had materially better weather but had been ignored.)
  • WW24, vicinity Norfolk Island South Pacific, 2009 (On 18 November 2009, an IAI Westwind on a medevac mission failed to make a planned night landing at Norfolk Island in unanticipated adverse weather and was intentionally ditched offshore because of insufficient fuel to reach the nearest alternate. The fuselage broke in two on water contact but all six occupants escaped from the rapidly sinking wreckage and were eventually rescued. The Investigation initially completed in 2012 was reopened after concerns about its conduct and a new Final Report in 2017 confirmed that the direct cause was flawed crew decision-making but also highlighted ineffective regulatory oversight and inadequate Operator procedures.)
  • A320, Khartoum Sudan, 2005 (On 11 March 2005, an Airbus A321-200 operated by British Mediterranean Airways, executed two unstable approaches below applicable minima in a dust storm to land in Khartoum Airport, Sudan. The crew were attempting a third approach when they received information from ATC that visibility was below the minimum required for the approach and they decided to divert to Port Sudan where the A320 landed without further incident.)
  • A320, vicinity Jaipur India, 2016 (On 27 February 2016, an Airbus A320 making an into-sun visual approach to Jaipur in hazy conditions lined up on a road parallel to the intended landing runway and continued descent until an EGPWS ‘TOO LOW TERRAIN’ Alert occurred at 200 feet agl upon which a go-around was initiated. The Investigation found that although the First Officer had gained visual reference with both road and runway at 500 feet agl, the Captain had seen only the road and continued asking the First Officer to continue descent towards it despite the First Officer’s attempts to alert him to his error.)

Related Articles

Further Reading

  • ICAO Doc 4444: PANS-ATM;

Flight Safety Foundation

The Flight Safety Foundation ALAR Toolkit provides useful training information and guides to best practice. Copies of the FSF ALAR Toolkit may be ordered from the Flight Safety Foundation ALAR website