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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:

  • C550, vicinity Cagliari Sardinia Italy, 2004 (On 24 February 2004, a Cessna 550 inbound to Cagliari at night requested and was approved for a visual approach without crew awareness of the surrounding terrain. It was subsequently destroyed by terrain impact and a resultant fire during descent and all occupants were killed. The Investigation concluded that the accident was the consequence of the way the crew conducted the flight in the absence of adequate visual references and with the possibility of a ‘black hole’ effect. It was also noted that the aircraft was not fitted, nor required to be fitted, with TAWS.)
  • C185, Smithers BC Canada, 2000 (On 27 September 2000, a Cessna 185, struck a snow covered hillside, probably while in controlled flight, en-route from Smithers BC, Canada.)
  • 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.)
  • B737, Mildura VIC Australia, 2013 (On 18 June 2013, a Boeing 737-800 crew en route to Adelaide learned that un-forecast below-minima weather had developed there and decided to divert to their designated alternate, Mildura, approximately 220nm away where both the weather report and forecast were much better. However, on arrival at Mildura, an un-forecast rapid deterioration to thick fog had occurred with insufficient fuel to divert elsewhere. The only available approach was flown to a successful landing achieved after exceeding the minimum altitude by 240 feet to gain sight of the runway. An observation immediately afterwards gave visibility 900 metres in fog with cloudbase 100 feet.)
  • A333, vicinity Wom Guam Airport, Guam, 2002 (On 16 December 2002, approximately 1735 UTC, an Airbus A330-330, operating as Philippine Airlines flight 110, struck power lines while executing a localizer-only Instrument Landing System (ILS) approach to runway 6L at A.B. Pat Won Guam International Airport, Agana, Guam. Instrument meteorological conditions prevailed during the approach. Following a ground proximity warning system (GPWS) alert, the crew executed a missed approach and landed successfully after a second approach to the airport.)


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