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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 Minimum Descent Altitude/Height or Decision Altitude/Height.

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 Minimum Descent Altitude/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;
(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:

  • AT75, vicinity Magong Taiwan, 2014 (On 23 July 2014, a TransAsia Airways ATR 72-500 crashed into terrain shortly after commencing a go around from a VOR approach at its destination in day IMC in which the aircraft had been flown significantly below the MDA without visual reference. The aircraft was destroyed and48 of the 58 occupants were killed. The Investigation found that the accident was entirely attributable to the actions of the crew and that it had occurred in a context of a systemic absence of effective risk management at the Operator which had not been adequately addressed by the Safety Regulator.)
  • T154, vicinity Smolensk Russian Federation, 2010 (On 10 April 2010, a Polish Air Force Tupolev Tu-154M on a pre-arranged VIP flight into Smolensk Severny failed to adhere to landing minima during a non precision approach with thick fog reported and after ignoring a TAWS ‘PULL UP’ Warning in IMC continued descent off track and into the ground. All of the Contributory Factors to the pilot error cause found by the Investigation related to the operation of the aircraft in a range of respects including a failure by the crew to obtain adequate weather information for the intended destination prior to and during the flight.)
  • 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.)
  • DH8A, Saulte Ste. Marie ON Canada, 2015 (On 24 February 2015, the crew of a Bombardier DHC8-100 continued an already unstable approach towards a landing despite losing sight of the runway as visibility deteriorated in blowing snow. The aircraft touched down approximately 140 metres before the start of the paved surface. The continued unstable approach was attributed by the Investigation to "plan continuation bias" compounded by "confirmation bias". It was also found that although the aircraft operator had had an approved SMS in place for almost six years, it had not detected that approaches made by the aircraft type involved were routinely unstable.)
  • B762, vicinity Busan Korea, 2002 (On 15 April 2002, a Boeing 767-200 attempting a circling approach at Busan in poor visibility crashed into terrain after failing to follow the prescribed procedure or go around when sight of the runway was lost. 129 of the 166 occupants were killed. The Investigation attributed the accident to actions and inactions of the pilots but noted that the aircraft operator bore considerable contextual responsibility for the poor crew performance. It was also concluded that ATC could have done more to manage the risk procedurally and tactically on the day and that ATM regulatory requirements did not adequately address risk.)

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 http://www.flightsafety.org/current-safety-initiatives/approach-and-landing-accident-reduction-alar