If you wish to contribute or participate in the discussions about articles you are invited to join SKYbrary as a registered user

 Actions

Visual References

From SKYbrary Wiki

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:

  • A320, vicinity Sochi Russia, 2006 (On 3 May 2006, an Airbus 320 crew failed to correctly fly a night IMC go around at Sochi and the aircraft crashed into the sea and was destroyed. The Investigation found that the crew failed to reconfigure the aircraft for the go around and, after having difficulties with the performance of an auto go-around, had disconnected the autopilot. Inappropriate control inputs, including simultaneous (summed) sidestick inputs by both pilots were followed by an EGPWS PULL UP Warning. There was no recovery and about a minute into the go around, a steep descent into the sea at 285 knots occurred.)
  • C501, vicinity Trier-Fohren Germany, 2014 (On 12 January 2014, the crew of a Cessna 501 on a private business flight with a two-pilot crew attempted to make an unofficial GPS-based VNAV approach in IMC to the fog-bound VFR-only uncontrolled aerodrome at Trier-Fohren. However, after apparently mis-programming the 'descend-to' altitude and deviating from the extended centre, the aircraft emerged from the fog very close to the ground and after pulling up collided with obstructions, caught fire and crashed killing all occupants. The Investigation noted an apparent absence of pre-flight weather awareness beyond the intended destination and that there was a suitable fog-free diversion.)
  • B738, vicinity Trivandrum India, 2015 (On 18 August 2015, a Boeing 737-800 made three unsuccessful ILS approaches at Cochin around dawn then diverted to Trivandrum where a day VOR approach was unsuccessful and a MAYDAY was declared due low fuel. Two further supposedly visual approaches were attempted there before a third such "visual" approach - which involved ignoring EGPWS PULL UP Warnings in IMC - was followed by a successful landing with 349kg fuel remaining. The Investigation found that aircraft safety had been jeopardised and that Cochin ATC had not communicated information on the deteriorating weather at Trivandrum. Relevant operator procedures were considered as inadequate.)
  • D328, Sumburgh UK, 2006 (On 11 June 2006, a Dornier 328 operated by City Star Airlines whilst positioning in marginal visibility for a day approach at Sumburgh, Shetland Isles UK, and having incorrectly responded to TAWS Class A warnings/alerts by not gaining safe altitude, came to close proximity with terrain . The approach was continued and a safe landing was made at the airport.)
  • MD83, vicinity Paris Orly France, 1997 (On 23 November 1997, a McDonald Douglas MD 83 being operated by AOM French Airlines on a scheduled passenger flight from Marseille to Paris Orly made an unintended premature descent almost to terrain impact at 4nm from the destination runway in day IMC before a go around was commenced. A subsequent approach was uneventful and a normal landing ensued. There was no damage to the aircraft or injury to the occupants.)


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